3. Waves Flashcards
What do waves transfer?
Energy
Waves transfer energy without transferring what?
Matter
Describe wave motion
No matter travels with waves as it travels between 2 points
Points on the wave vibrate back and forth about a fixed point
What is a wavefront?
A way of viewing waves from above
What is meant by the speed of a wave?
The distance travelled by a wave per second
What is meant by the frequency of a wave?
Number of waves passing any point per second
What is the SI unit for frequency?
Hertz (Hz)
What is the formula for frequency?
f= 1/period
What is meant by period?
Time taken for 1 oscillation
What is the SI unit for period?
Seconds (s)
What is meant by the term wavelength?
Distance from a point on one wave to the same point on the next wave
What is the SI unit for wavelength?
Metres (m)
What is the formula for speed?
v = fλ
What is meant by the term amplitude?
The height of a wave measured from the middle of the wave
What is a transverse wave?
Waves in which oscillations are perpendicular to direction of travel
What is a longitudinal wave?
Waves in which oscillations are parallel to direction of travel
What are 2 differences between transverse and longitudinal waves?
- Oscillations and direction of travel
- Transverse waves have peaks and troughs and longitudinal waves have compressions and rarefactions
What are 3 wave effects?
Reflection
Refraction
Diffraction
What is reflection?
The bouncing back of a wave
What is refraction?
The change in speed of a wave when it passes from one medium to another
What is diffraction?
The spreading of a wave
What are the laws of reflection?
- Angle of incidence = angle of reflection
- The incident ray, reflected ray and the normal all lie in the same plane
What are the effects on speed, frequency and wavelength of a wave that is reflected?
No effect
What are 3 effects of refraction of a wave into a different medium?
Change in speed
Change in wavelength
Change in direction
What is the effect on a wave travelling from a more dense medium to a less dense medium?
Speed decreases
Wavelength decreases
Bends away the normal
What is the effect on a wave travelling from a less dense medium to a more dense medium?
Speed increases
Wavelength increases
Bends towards from the normal
Which property of a wave is not affected by refraction?
Frequency
Is shallow water less dense or more dense than deep water?
Less dense
Is shallow water less dense or more dense than deep water?
Less dense
What are 2 factors that influence diffraction?
- Size of the gap
- Wavelength
How does the size of a gap affect diffraction?
Wider gaps produce less diffraction
How does wavelength affect diffraction?
Greater wavelength produces more diffraction
What 3 properties are not affected by wavelength?
Speed
Wavelength
Frequency
What are 3 characteristics of an optical image formed by a plane mirror?
Same size as the object
Same distance behind the mirror as the object is in front of it
It is directly in line with the object
Is the image in a plane mirror virtual or real?
Virtual
Exam tip ; )
When drawing light waves being reflected take care to get the angle about right.
If they are slightly out it won’t be a problem, but if there is an obvious difference between the angle of incidence and the angle of reflection then you will probably lose a mark.
Describe an experimental demonstration of the refraction of light
Place the glass block on plain paper and draw around the block using a pencil
Use a ray box to project a single ray of light towards the glass block
Using a pencil, mark the points before it reaches the glass block and where it hits the glass block
Mark the points where it leaves the glass block and after it has left the glass block
Connect the points using a ruler and pencil
Repeat the process with the ray striking the block at different angles
Use Snell’s Law
What is Snell’s Law?
As light travels from a less dense medium to a more dense medium it slows down and bends towards the normal
What is refractive index?
Degree at which light is bent by the second medium
What is the relationship between angle of incidence and angle of refraction given by Snell’s Law?
n = sin i ÷ sin r
What is the formula for refractive index?
n = speed of light in vacuum ÷ speed of light in medium
What is critical angle?
Angle of incidence that gives an angle of refraction of 90°
Light travels from a more dense medium to a less dense medium
What is the formula for critical angle?
n = 1 ÷ sin c
Describe internal reflection
Light travels from a more dense to a less dense medium
Most of the light is refracted
A small amount is reflected
Describe total internal reflection
Light travels from a more dense to a less dense medium
Angle of incidence is greater than the critical angle
All of the light is reflected
What are 2 conditions for total internal reflection?
Light must be travelling from a more dense to a less dense medium
Angle of incidence must be greater than the critical angle
Describe and explain the action of optical fibres particularly in medicine and communications technology
Total internal reflection is used to reflect light along optical fibres
This allows the transmission of data at high speeds on the internet
Optical fibres are used in medicine in order to see within the human body
Exam tip ; )
When drawing light reflecting down an optical fibre, make sure that each time it reflects the angle of reflection is equal to the angle of incidence.
What is the principal focus?
Point where rays parallel to the lens focus
What is the focal length?
The distance of the principal focus from the lens
What is the optical centre?
The centre of the lens
What is the principal axis?
Line that goes through the optical centre
What image will form if the object is between the centre and the focal length?
Virtual
Enlarged
Upright
What image will form if the object is between the focal length and twice the focal length?
Real
Enlarged
Inverted
What image will form if the object is placed exactly on twice the focal length?
Real
Same size
Inverted
What image will form if the object is beyond twice the focal length?
Real
Diminished
Inverted
Are real or virtual images projected onto a screen?
Real images
Describe the use of a single lens as a magnifying glass
The lens should always be held close to the object
What is a real image?
An image formed by the convergence of light rays
What is a virtual image?
An image formed when the rays appear to come from behind the lens
What is a converging lens also know as?
Convex lens
What is a use of dispersion of light?
Separating white light
How many colours are there in the spectrum of light?
Seven
What are the 7 colours in the spectrum of light?
ROY G BIV
Which of the 7 colours of light has the greatest wavelength?
Red
Which of the 7 colours of light has the smallest wavelength?
Violet
What causes the colours of light to bend by different amounts?
They slow down by different amounts
What is the relationship between wavelength and speed in prism?
The greater the wavelength, the slower the speed
What is light of a single wavelength or single frequency known as?
Monochromatic
What are the main features of the electromagnetic spectrum?
Radio waves
Microwaves
Infrared
Visible light
Ultraviolet
X-rays
Gamma rays
What mnemonic is used to list the features of the electromagnetic spectrum?
Roman Men Invented Very Useless X-ray Guns
Which of the 7 features of the electromagnetic spectrum has the greatest wavelength?
Radio waves
Which of the 7 features of the electromagnetic spectrum has the shortest wavelength?
Gamma rays
What is the speed of electromagnetic waves in a vacuum?
3.0 × 10^8
What are radio waves used for?
Radio and television communications
What are microwaves used for?
Satellite television and telephones
What is infrared used for?
Electrical appliances
Remote controllers for television
Intruder alarms
What are X-rays used for?
Medicine and security
What are the dangers of microwaves?
High levels of microwaves cause heating of internal organs
What are the dangers of X-rays?
Can harm cells and cause cancer
Why are high levels of microwaves dangerous?
Water molecules absorb microwaves strongly
Why are X-rays dangerous?
They are highly ionising
How are sound waves produced?
Vibrating sources
What type of wave are sound waves?
Longitudinal
What is a compression?
Space where molecules are bunched together
What is a rarefaction?
Space where molecules are spaced out
What is the approximate range of audible frequencies for a healthy human ear?
20 Hz - 20,000 Hz
What is ultrasound?
Sound waves with a frequency greater than 20,000 Hz
What is needed to transmit sound waves?
A medium
Describe an experiment to determine the speed of sound in air
Two observers are set apart at a known distance
Observer A fires a gun
Observer B starts the stopwatch when he sees the puff of smoke
Observer B stops the stopwatch when he hears the sound
Use the formula speed = distance ÷ time
Observers switch position and repeat the experiment
Values are averaged to obtain speed of sound
What is the speed of sound in gases?
330 m/s
What is the speed of sound in liquids?
1,500 m/s
What is the speed of sound in solids?
5,000 m/s
Which property of a sound wave is related to loudness?
Amplitude
Which property of a sound wave is related to pitch?
Frequency
How amplitude affect loudness?
Greater amplitude results in greater loudness
How frequency affect pitch?
Greater frequency results in higher pitch
What is an echo?
Reflection of a sound wave
What type of wave are light waves?
Transverse
Why does aluminium reflect light well?
Smooth, shiny surface, gives clear image as reflect light regularly
What is the law of reflection?
angle of incidence = angle of reflection
i=angle of incidence
r=angle of reflection
What is a normal?
imaginary line 90’’ to surface of object
what is lateral inversion?
when left appears to be right and right appears to be left in a mirror
what is refraction?
change of direction of a wave as it enters different medium
due to change in speed of wave
the frequency of a wave never changes!
what happens when light enters a more dense medium?
how does it refract?
bends towards the normal
denser substance -> rays slow down
what happens when light leaves the glass block and enters the air (less dense medium)?
how does it refract?
bends away from the normal
- paralell with ray of incidence
this is because the medium is less dense, light rays speed up
Why do birds not aim at the fish they see in the water, but instead a location next to it?
refraction!
why does the speed change?
refraction
medium changes
why does the frequency stay constant?
refraction
same number of waves pass a point each second
why does the wavelenth change?
refraction
waves travel a smaller distance between when they are created
How is white light split by a prism?
different colours refracted by different amounts, as slowed down in varying amounts by the glass
What is refractive index?
equation
refractive index = speed of light in a vaccuum/air / speed of light in a substance
No units! should be a small number (1-2.5)
n = C/Cs
eg speed of light (300 000 000 m/s) divided by speed in water (225 000 000 m/s) = 1.33
when you plot a graph of sin i (y) sin r (x), what is represented by the gradient of this directly proportional relationship?
refractive index
what is the equation linking refractive index, sin (i) and sin (r)?
n = sin (i) / sin (r)
n = refractive index
what is total internal reflection?
when light moves from a denser to less dense medium, instead of refracting, all the light is reflected
what are the conditions for total internal reflection?
light must be travelling from a higher to lower refractive index (from dense to less dense material, eg glass to air)
Angle of incidence is larger than critical angle
what is the equation that links refractive index with critical angle?
total internal reflecton
sin c = 1/n
sin critical angle = 1/refractive index
eg glass critical angle = sinc = 1/1.5
c = sin-1 (1.5)
c= 41.8”
what is the critical angle?
angle of incidence (which is critical angle when the angle of refraction is 90”)
what are uses of total interal reflection?
optical fibres (communication, beam of light enters optical fibres, refracted as enters the fibre, bu then travels down the fibre through repeated total internal reflection)
endoscopy
why are diamonds so sparkly?
have high refractive index, means a small critical angle, thus large proportion of light is totally internally reflected -> v sparkly (if light ray larger than critical angle)
What do waves do?
Transfer energy without transferring matter.
Mechanical waves
A vibration that travels through a substance.
Longitudinal waves
Waves in which the vibrations are parallel to the direction of energy transfer.
Transverse waves
Waves in which the vibrations are perpendicular to the direction of energy transfer.
Electromagnetic waves
Can travel through a vacuum, no medium is needed.
Examples of mechanical waves
sound, water, seismic
Examples of electromagnetic waves
light, radio, micro
Examples of Transverse waves
All electromagnetic waves
Example of longitudinal waves
Sound
Amplitude
Height of the wave crest.
The bigger the amplitude of the waves…
…. the more energy the waves carry.
Wavelength
The distance from one wavelength to the next.
Frequency
The number of wave crests passing a fixed point every second.
Speed of waves
Distance travelled by a wave crest every second.
Wave speed (m/s) =
Frequency (Hz) x Wavelength (m)
Straight waves
Plane waves
Reflection
The change of direction in a light ray or wave at a boundary when a wave/ray stays in the incident medium.
Refraction
The change of direction of a light ray when it crosses a boundary between two transparent substances.
Diffraction
The spreading of waves when they pass through a gap or around the edges of an obstacle.
The smaller the hole…
… The greater the diffraction
When is diffraction most noticeable?
When the hole is the same size as the wavelength of the wave.
What can diffraction cause?
Bad TV and Radio connection
Interference
Reinforcement or cancellation of waves when two sets of identical waves overlap.
When waves overlap crest to crest…
… constructive interference/ reinforcement takes place
What waves overlap crest to trough…
destructive interference/ cancellation takes place.
Electromagnetic Spectrum
Smallest - Largest:
Gamma
X-ray
Ultraviolet
Visible
Infrared
Micro
Radio
Units of electromagnetic wave measurement from smallest to largest
Picometre
Nanometre
Millimetre
Kilometre
How fast do electromagnetic waves travel in a vacuum?
300 million m/s
White Light
Light from ordinary lamps and the sun
The hotter an object is…
… The more infrared radiation it emits.
How does infrared radiation affect the body?
It can damage or kill skin cells by heating them up.
Optical fibres
The glass fibre used to send light signals along.
Uses infrared radiation.
4 uses of infrared radiation
Optical fibres
remote control handsets
infrared scanners
infrared handsets
The shorter the length of radio waves:
The more information they can carry.
The shorter their range.
The less they spread out.
What are microwaves used for?
Satellite phones
TV links
Satellite TV
(Can travel between satellites, don’t spread out much so the signal doesn’t weaken as much.)
What are radio waves
TV broadcasting
(Can carry more information than longer radio waves)
What are radio waves >1m used for?
Local Radio Stations
Have limited range
What are radio waves >100m used for?
National and International Radio Stations
Very large range
What do electromagnetic waves carry?
Information
What effect does UV radiation have?
It is harmful to human eyes and can cause blindness.
What produces gamma rays?
Radioactive substances when unstable nuclei release energy.
What produces x rays?
When particles moving at high speeds are stopped.
Which are more penetrative: X or Gamma rays?
Gamma, they have shorter wavelengths.
Applications of X-Rays
X- Rays
To detect internal cracks in metal
3 Uses of Gamma Radiation
> Killing bacteria in food
Sterilising surgical equipment
Killing cancer cells.
Safety concern of X-Ray and Gamma
Causes ionisation, which can result in cell mutation and death.
How an X-Ray works
X-Rays from an X-Ray tube are directed at the patient. A lightproof cassette is placed in the other side of the patient.
X-Rays pass through soft tissue, but are absorbed by bones, teeth and metal.
Where the X-Rays reach the flat-panel detector inside the lightproof cassette it turns darker and creates a clear impression of the bones etc.
How to get an X-Ray of an organ.
Give the patient a contrast medium that absorbs x-rays before their scan.
Flat Panel Detector.
A small screen that contains a CCD (charge coupled detector), which converts X-Rays to light. The light creates electronic signals which are sent to a computer.
CT scanner
Uses X-rays to produce a digital image of any cross section in the body or a three-dimensional image of the body.
Can sound waves travel through a vacuum?
They are mechanical: no.
What speed does sound travel at?
340m/s
What is a humans frequency range?
20 - 20 000 Hz
Echoes
Sound waves reflected from a smooth, hard surface.
Loud and High Pitched
.
Loud and Low Pitched.
.
Increasing the loudness of a sound…
… Increases its amplitude.
Increasing the frequency of a sound…
…Increases its pitch.
Ultrasound Waves
A sound wave undetectable to the human ear (too high)
Positives of ultrasound
Non-ionising
Produces images of organ tissues as well as bones.
How does an ultrasound transducer work?
The waves it emits are partially reflected by different tissue boundaries in its path.
These return to the transducer as a sequence of pulses that build up an image of the internal body.
Distance travelled by an ultrasound pulse =
speed of ultrasound waves in body tissue x time taken.
Angle of incidence =
Angle of reflection
Virtual Image
An image that cannot be projected on a screen.
Real Image
An image that can be projected on a screen.
Image formation by a plane mirror
.
When light enters a more dense medium…
… it refracts towards the normal
When light enters a less dense medium…
… it refracts away from the normal
Dispersion
The splitting of white light into the colours of the spectrum.
Snell’s Law
refractive index = speed of light in a vacuum (air) / speed of light in the medium.
Refractive Index
Measures how much a medium is capable of refracting light.
When a light ray travels from a transparent medium to air at a non-zero angle of incidence:
The light ray is refracted away from the normal
the larger the angle of incidence, the larger the angle of refraction.
Total Internal Reflection
The total reflection af a light ray in a transparent substance when it reaches a boundary with air or another transparent substance. Only happens if the angle of incidence is bigger than the critical angle.
Critical Angle
The angle of incidence of a light ray in a transparent medium that produces refraction along a boundary.
Total Internal Reflection only happens when…
… light is trying to enter a less dense medium.
Endoscope
Uses TIR to see directly inside the body.
Concave (Diverging) Lens
.
Convex (Converging) Lens
.
Uses of a convex lens
Magnifying Glass, In a camera to create a clear image of a far off object.
Uses of a concave lens
To correct short sightedness.
Focal Length
The distance from the centre of a lens to where the light rays focus (or, in the case of a concave lens, appear to diverge from.)
Real Image, from a convex lens.
.
Virtual Image, from a concave lens
.
Magnification of an image =
Image height/ Object Height
How to construct a real image/converging lens diagram
To form a real image using a converging (convex) lens, the object must be beyond the principal focus, F, of the lens.
Ray 1 is parallel to the axis and is refracted through F
Ray 2 passes straight through the centre of the lens
Ray 3 passes through F and is refracted parallel to the axis
How to construct a virtual/Converging lens diagram
.
How to construct a virtual/Converging lens diagram
How to construct a virtual/Diverging lens diagram
.
How does a camera work?
.
What does ‘real is positive’ mean?
Real images are given positive focal lengths in the formula, virtual negative.
1/focal length =
1/distance from object to lens + 1/distance from lens to image
(1/u + 1/v = 1/f)
A diverging lens…
… always gives a virtual image.
Iris
Coloured ring of muscle that controls the amount of light entering the eye.
Aqueous Humour
Transparent watery liquid that supports the front part of the eye.
Cornea
Transparent layer that protects the eye and helps to focus light onto the retina.
Pupil
the central hole formed by the Iris. Light enters the eye through the pupil.
Ciliary Muscles
Attached to the lens by Suspensory Ligaments.The muscles change the thickness of the eye lens.
Eye Muscles
Move the eye in the socket.
Optic Nerve
Carries nerve impulese from the retina to the brain.
Blind Spot
Region of the retina that is not sensitive to light (no light sensitive cells present)
Retina
The light sensitive cells around the inside of the eye.
Vitreous Humour
Transparent jelly-like substance that supports the back of the eye.
Eye Lens
Focuses light onto the retina.
Type of lens (Eye vs Camera)
Variable focus converging lens
Fixed focus convergin lens
Focusing Adjustment (Eye vs Camera)
Ciliary muscles adjust lens position.
Manual adjustment of lens position.
Image produced (Eye vs Camera)
Both real, inverted, magnification less than 1.
Image detection (Eye vs Camera)
Light sensitive cells on the retina
Photographic Film (or CCD sensors in digital camera)
Brightness Control (Eye vs Camera)
Iris controls width of pupil
Adjustment of aperture ‘stop’
Short Sight
An eye that can only focus on near objects.
Corrected with a diverging lens.
Long Sight
An eye that can only see far away objects.
Corrected with a converging lens.
Power of a lens (D (dioptre)) =
1/ focal length (m)
The higher the refractive index of a lens material…
… The flatter and thinner the lens can be.
Define a wave
A disturbance or oscillation that travels through space and matter accompanied by the transfer of energy
What is propagation of wave?
Direction in which waves travel
What is propagation of wave?
Direction in which waves travel
What are transverse waves
Vibrations of the particles are perpendicular to the direction in which energy transfer
Examples of transverse waves
Water waves seismic waves electromagnetic waves
What are longitudinal waves?
Vibrations of the particles are parallel to the direction in which energy transfer
Give examples of longitudinal waves
Sound waves and earthquake waves
What do longitudinal waves have?
Compressions and rarefactions
What is the wavelength?
Distance between two successive equivalent points.
What is frequency?
Number of waves per unit time- Hertz Hz
What is the equation for frequency?
F- number of waves/time
What is a period?
The time taken for one complete oscillation
What is the equation for a period?
Time/ number of waves
What is the amplitude?
The maximum displacement from the horizontal axis to the peak
Equation for speed of sound
Wave speed= Frequency * Wavelength
What is a ray?
Direction of travel- perpendicular to wave fronts
What is a wave front?
Surface over which an optical wave has a constant phase
What do circular waves have?
Circular wave fronts
What do plane waves have?
Plane wave fronts
What does the pitch depend on?
The frequency of the source of sound
What does a high frequency produce?
High pitch noise
What does a large amplitude produce?
A louder sound
What type of wave is a light wave?
Transverse waves
What is the speed of light?
3 * 10^8 m/s
Where does light travel faster?
In low dense media
What type of wave in a sound wave?
Longitudinal
Where does sound travel fastest?
In denser media
Where does sound travel fastest?
In denser media
What is the speed of sound in air?
330 m/s
What is the speed of sound in water?
1500 m/s
What is the speed of sound in solid?
5000 m/s
How does light travel?
In straight lines
Give the three different wave effects
Reflection, Diffraction and Refraction
What happens to light waves when they enter a dense medium?
Bend towards the normal
What happens to sound waves when they enter a dense medium?
Bend away from the normal
What is the range of human hearing?
Between 20Hz and 20 kHz
What is an ultrasound?
Frequencies with above 20kHz
What are luminous objects?
Emit their own light
What are non-luminous objects?
They bounce off the light or they reflect the light so we can see them
What is monochromatic light?
Waves that have a single frequency
When does reflection of light happen?
When the light meets a boundary like a mirror, paper and surface of water
What is the normal ray?
It is a virtual line that is perpendicular to the surface at the point of incidence
What is the incident angle?
Angle between normal and incident ray
What is the reflected ray?
Angle between the normal and reflected ray
What are the laws of reflection?
Angle of incidence= Angle of reflection
Incident wave, reflected wave and the normal lie in the same plane
What will happen to the wavelength, frequency and the speed after the reflection?
Nothing will change
What is the image produced from reflection?
Same size, up right down, literally inverted, and virtual
How can we distinguish an echo?
0.1 s
How are good echo produced?
The distance between the reflector and the sound source is more than 30 meters.
The area of a reflector is large compared to the wavelength of the incident sound
The incident sound is high pitched
What do we use echo for?
To survey the depth and nature of the seabed
What is refraction?
When waves enters from one medium to the other medium, it changes its direction depending upon the angle of incidence because of the change in speed
What happens when a ray of light travels from a dense medium to a less dense medium?
Its speed and wavelength increases and the ray bends away
What happens when white light enters a prism?
Red is deviated bent off course least by prism- violet light is deviated most
What is the order of the colours in the spectrum?
Red
Orange
Yellow
Green
Blue
Indigo
Violet
Give the refractive index equation
Speed of light in air/speed of light in medium
What is snell’s law?
n1 sin θ1= n2 sinθ2
What are the conditions of total internal reflection?
The light must travel from denser to to less dense
Its incident angle more than critical angle
What is the critical angle equation ?
Sinθ= 1/n
What is an optical fibre?
A thin rod of high quality glass and very little light is absorbed by the glass
What method does the optical fibre use?
Undergoes repeated total internal reflection even when the fibre is bent
Where are optical fibres used?
Used in endoscopes to allow surgeons to see inside their patients and they can carry huge amounts of information as pulses of light.
What is the focal point?
Where parallel light rays converge after the lens
Describe the image formed when an object is very far way from a convex lens 3F.
Image is real, inverted and the image is smaller
Describe the image formed when when an object is two focal points from a convex lens.
Real inverted and smaller
Describe the image formed is between one and two focal lengths from the convex lens.
Real, inverted and larger
Describe what happens when an object is one focal length from a convex lens
The lines do not intersect
Describe the image formed is half focal lengths from the convex lens.
virtual, enlarged upright
What is diffraction?
The spreading out of waves as they pass through a gap or by an obstacle
What does a big gap in the barrier cause?
The disturbances are very small
What does a small gap cause?
The circular disturbances are massive compared to the undisturbed wave front
When does maximum diffraction happen?
When the width of the gap is equal to the wavelength of the waves
How can sound diffract?
Through a doorway or around buildings
What type of sound diffracts the best and why?
Low pitch- because they have a long wave length compared with the width so they spread our more
What happens when ultrasound is diffracted?
There is little spreading which makes sharp focusing of ultrasound easier- good for medical scanning
What are properties of EM waves?
They travel the same speed in a vacuum
What waves are EM waves?
Transverse waves
Give the order of the EM waves
Radio
Microwaves
Infrared
Visible light
Ultraviolet
X-ray
Gamma Ray
What are radio waves used for?
Amateur FM radio- TV broadcasts
What are microwaves used for?
Mobile phones
Heating effect in microwaves
TV and communications
What is infrared used for?
Radiant heaters, toasters
TV remote controllers
Security alarms
Optical fibers
What is ultraviolet used for?
Sterilising equipment to kill bacteria
Why is ultraviolet dangerous?
It can cause skin cancer and may damage the retina and cause blindness
What is X-ray used for?
Treat cancer
Detect weapons in luggage
To take photographs that reveal flaws of metals
What is gamma ray used for?
To take photographs
Killing bacteria
Treat cancer
Sterilizing food and medical equipment
Wavelength = ?
Units?
Wave speed = wavelength * frequency
Wave speed (m/s)
Wavelength (m)
Frequency (Hz)
Frequency = ?
F = 1/T
Frequency (Hz)
Refractive index = ?
using the speed of light
Refractive index = speed of light in air / speed of light in medium
or
n = C in air / C in medium
Refractive index = ?
using sin
Refractive index = sin(i) / sin(r)
Two types of waves?
Define
Give examples of each (3)
LONGITUDINAL
The vibrations of the wave are along the same direction of energy transfer
Ultrasound, seismic waves and slinky when you push the end
TRANSVERSE
The vibrations of the wave are at 90 degrees to the direction of energy transfer
EM waves, ripples of water and slinky spring when waved up and down
Define total internal reflection
When angle C (critical angel) is smaller than the angel of incidence. This means that all rays are reflected and none are refracted.
Explain polarisation and give an example
Only transverse waves can be polarised.
Transverse waves are polarised when their vibrations are restricted to one plane only
e.g.
Sunglasses that reduce glare
When does it happen?
1-Refraction
2-Diffraction
3-Reflection
1-Wave travels through a material but changes direction. The angel of refraction is less than the angel of incidence
2-Waves spread out when they meet a gap. The more narrow the gap the more the wave is diffracted
2-When waves rebound off material such as a plane mirror
Critical angel?
Sin(C) = ?
1/n
List the EM waves starting from the one with the lowest frequency
RADIO WAVES
MICRO WAVES
INFRARED
VISIBLE
ULTRAVIOLET
X-RAY
GAMMA RAY
Which property of a sound wave should be increased in order to make the sound louder?
amplitude
Which property of a sound wave should be increased in order to make a higher pitched sound?
frequency
What equation can we use to measure frequency of a sound wave on an oscilloscope?
frequency (Hz) = 1/t (s)
What is the range of human hearing?
20 hz - 20,000 hz
What type of waves are sound waves?
longitudinal
Sound waves can be ________ and __________.
Sound waves can be reflected and refracted.
Describe how you could measure the speed of sound in air
Use the tape to measure a distance of 50 metres from the wall.Now clap your hands and check you can clearly hear an echo from the wall. Make sure the echo isn’t coming from other walls in the area. The time it takes sound to run 100 metres is the time difference between when you clap and when you hear the echo.However, measuring that single short burst of time is difficult.Now clap repeatedly in time with the echo, so that you can only hear your own clap (the echo is masked by your next clap)Now measure the time it takes to clap 10 times. Get a friend to start the stopwatch at the first clap and end it when you hear the echo of the 10th clap.We now know how long it takes for sound to travel 1 kilometre.Now we can calculate the speed of sound using: speed = distance/time
What type of waves are light waves?
transverse
Light waves can be ________ and __________.
Light waves can be reflected and refracted.
Describe an experiment to investigate the refraction of light.
Get two identical cups and place them side by side. Place a coin at the bottom of both cups. Fill one cup with water. Now look at the coins. Do they appear to be in the same place or even the same depth?You can also make a hidden coin appear as if by magic. This time just use one cup. Put the coin in against one side of the cup. Move your head until you just can’t see the coin any more. Now pour in water and, alla kazam, it appears!
Describe an experiment to determine the refractive index glass.
We can find the value of n for a glass block by using a ray box and a semicircular block.To do the experiment it is necessary to try a few angles of incidence and measure both the angle of incidence and the refracted angle. You would complete a table as you go.
Describe the role of total internal reflection in the transmission of information along optical fibres.
Light entering a periscope meets a triangular prism. It is then reflected down the tube of the periscope where it meets another prism. Finally, it is reflected at this prism out to the observer.
State the meaning of the critical angle c
Angle of incidence that gives an angle of refraction of 90°
Light travels from a more dense medium to a less dense medium
State the meaning of the critical angle c
A material has a reflective index of 1.5. Calculate the size of x.
sin i / sin r = n sin 48 / sin r = 1.5 sin 48 / 1.5 = sin r 0.743/1.5 = sin r 0.495 = sin r r = sin-1 0.495 r = 29.7o x = 90 - 29.7 = 60.3o
A material has a refractive index of 1.45. Calculate the size of x.
sin i / sin r = n sin i / sin 30 = 1.45 sin i / 0.5 = 1.45 sin i = 1.45 x 0.5 sin i = 0.725 i = sin-1 0.725 = 46.5o x = 90 - 46.5 = 43.5o
A material has a refractive index of 1.35. Calculate the size of x.
53.7
A material has a refractive index of 1.3. Calculate the size of x.
sin i / sin r = n sin i / sin 40 = 1.3 sin i / 0.643 = 1.3 sin i = 1.3 x 0.643 sin i = 0.836 i = sin-1 0.725 = 56.7o x = 90 - 56.7 = 33.3o
Describe the role of total internal reflection in the transmission of information along optical fibres.
In recent years, the biggest use of total internal reflection is in transmitting information using fibre optics. Light travelling along an optical fibre is continuously reflected along the length of the fibre. No light can escape from the fibre. The light can be modulated to carry information.
Name the uses and dangers of radio waves
Uses - Broadcasts and communication.Dangers - none.
Name the uses and dangers of microwaves
Uses - Cooking, satellite transmissions, mobile phonesDangers - Internal heating of body tissue
Name the uses and dangers of infrared
Uses - Heaters, thermal imaging, night vision equipmentDangers - Burns skins
Name the uses and dangers of visible light
dangers - strong light causes damage to vision
Name the uses and dangers of ultraviolet
skin cancer and blindness
Name the uses and dangers of x-rays
mutations in cells and severe burns to the skin
Name the uses and dangers of x-rays
mutations in cells and severe burns to the skin
Name the uses and dangers of gamma rays
cancers and cell mutation
How can we protect ourselves from the dangers of microwaves
small metal grid in microwave door prevents microwaves getting out
How can we protect ourselves from the dangers of infra-red
distance - don’t get too close to the hot object (e.g. electric fire)
How can we protect ourselves from the dangers of visible ligtht
we are adapted to reduce intake of light through our eyes when too bright - the pupil in our eyes becomes smaller in bright light and bigger in dim light.Wearing sunglasse or dark glass. e.g. welders wear dark glass.
How can we protect ourselves from the dangers of ultraviolet
Eyes - sunglasses, hatsSkin - suncream or sunblock. Wearing clother or special garments like rashies.
How can we protect ourselves from the dangers of How can we protect ourselves from the dangers of x-rays
The technician sits behind a lead screen or lead infused glass to protect from x-rays.
How can we protect ourselves from the dangers of gamma rays
Nuclear power stations have massive sheilding from lead and concrete
What type of wave is this?
Transverse
What type of wave is this?
Longitudinal
A sound wave has a frequency of 1000Hz. Calculate the period of one wave.
T = 1/f
T = 1/1000
T = 0.001 s
A water wave has a period of 5s. Calculate the frequency of the waves.
f = 1/T
f = 1/5
f = 0.2Hz
Calculate the period of a wave with frequency 200Hz.
Calculate the period of a wave with frequency 200Hz.
T = 1/f
T = 1/200
T = 0.005 s
Calculate the frequency of a wave with a period of 0.02s.
f = 1/T
f = 1/0.02
f = 50Hz
A sound wave has a frequency of 4000Hz and a wavelength of 8.5 cm. Calculate its speed.
v = fλ
v = 4000 x 8.5cm
v = 4000 x 0.085 m
= 340 ms-1
Calculate the frequency of a radio signal with wavelength 250 m.
v = fλ
f = v/λ
All electromagnetic waves travel at the same speed of 3 x 108 m/s.
f = 3 x 108/250
f = 3 x 108/2.5 x102
f = 3 x 108-2/2.5
f = 3 x 106/2.5
f = 1.2 x 106 Hz
Calculate the frequency of a sound wave of wavelength 10cm travelling at 330 ms-1
v = fλ
f = v/λ
f = 330/10cm
f = 330/0.1
f = 3300Hz
Calculate the wavelength of red light which has a frequency of 4.6 x 10 ^14 Hz.
v = fλ
λ = v/f
λ = 3 x 10 ^8/4.6 x 10 ^14
λ = 3 x 10 ^(8-14)/4.6
λ = 3 x 10 ^-6/4.6
λ = 0.652 x 10 ^-6
λ = 6.52 x 10 ^-7m
Calculate the frequency of violet light which has a wavelength of 450nm
v = fλ
f = v/λ
f = 3 x 10 ^8/450nm
f = 3 x 10 ^8/450 x 10^-9
f = 3 x 10 ^8/4.5 x 10^-7
f = 3 x 10 ^8-(-7)/4.5
f = 3 x 10 ^15/4.5
f = 0.667 x 10^15
f = 6.67 x 10^14Hz
Name the parts of the wave
A - Crest
B - Amplitude
C - Wavelength
D - Trough
The number of waves that pass a point every second is called it’s __________________.
frequency
The time it takes one wave to pass a point is called a _________.
period
Describe diffraction.
Diffraction is when waves bend around obstructions, edges or through gaps.
How to waves look when they diffract through a gap the same size as the wavelength?
The waves are circular
How do waves look when they diffract through a large gap?
The waves will be straight with curved edges.
What are waves?
a means of transferring energy
What doesn’t happen with waves?
There is no transfer of matter
What are transverse waves?
Waves where the direction of energy transfer is perpendicular to the direction of oscillations
What are longitudinal waves?
Waves where the direction of energy transfer is along the direction of oscillations
What is an example of a transverse wave?
light, waves travelling on the surface of water
What is an example of a longitudinal wave?
sound
What is amplitude?
the maximum movement of particles from their resting position caused by a wave
What happens when waves strike a concave barrier?
They become curved and are made to converge
What happens when waves strike a convex barrier?
They are made to diverge and spread out.
What happens when waves enter a shallower region?
their wavelength becomes shorter and because the frequency is constant the velocity also decreases
What happens when the waves enter the deeper region?
their wavelength increase and so does the velocity
What is necessary for refraction to occur?
the boundary between the shallow water and the deep water is at an angle to the direction in which the waves are moving
What happens when waves enter shallow vs deep region?
Shallow: bend towards normal and slow down
Deep: bend away form the normal and speed up
What are the common features to all electromagnetic waves?
they are all transverse
they all travel at 3x108 m/s
they can all be diffracted, refracted and reflected
they all transfer energy
What is the wave with the longest wavelength?
radio
Which wave has the most penetrating power?
gamma
Which is the most high frequency wave?
gamma
What are radio waves used for?
broadcasting and communication
reflect of ionosphere
How are radio waves produced?
They are emitted by a transmitter, cross an aerial and the information is receives as they are detected
What detects radio waves?
TV aerials and radio
What are the uses of microwaves?
cooking, radar and satellite transmissions
How do microwaves heat food?
The waves cause water to vibrate more and increase there amplitude. This increase in kinetic energy is essentially an increase in temperature and so the water molecules become very hot.
The food is cooked throughout not just on the outside
What are the dangers of microwaves?
They can heat human tissue
How are the dangers of microwaves reduced?
Microwaves have metal screens that reflect them and keep them inside the oven.
How are microwaves used for communication?
The waves pass through the Earth’s atmosphere and are used to carry signals to orbiting satellites.
They also carry messages sent from phones so therefore can pass through solids (glass/brick)
What do all objects do?
emit IR
What makes more IR be emitted?
If something is hotter
What detects IR?
skin, blackened thermometers, IR cameras
What are the uses of IR?
night vision equipment, remote controls for TV, stereo and videos
cooking in grills and toasters
optical fibres
Why are IR used for remotes?
They have a low penetrating power and so are unlikely to interact with other signals.
What are the dangers of IR?
skin burning and if cells absorb too much they are killed/damaged
What emits visible light and detects it?
luminous objects
detected by the eye, cameras, LDRs and photographic film
What are the uses of Visible light?
seeing
light from lasers is used to read compact discs and barcodes
optical fibres: communication and seeing inside the body
Which colour has the longest wavelength?
red light
What is the frequency of red light like?
low frequency
What are the dangers of UV light?
blindness - harmful to eyes
skin cancer - damage to skin
How does UV light cause cancer?
causes cancer by ionizing cells under skin surface
What is UV light used in?
UV tanning lamps
some chemicals fluoresce when exposed to UV light
What is helping to reduce UV light?
ozone absorbs it
What does fluorescence mean?
an object that absorbs UV light and emits visible light
What emits X-rays?
X-ray tubes
What detects X-rays?
photographic film
What are X-rays used for?
in radiography to observe internal objects of the body
security checks in airports
in the industry to check the internal structures of objects for cracks etc
What are the dangers of X-rays?
excessive exposure can cause cancer
How can you protect against X rays?
stand behind a lead screen
protective clothing
How can you protect against X rays?
stand behind a lead screen
protective clothing
What are gamma rays emitted by?
radioactive material
What are gamma rays detected by?
Geiger- Muller tube
What are the uses of gamma rays?
sterilise medical equipment
kill micro-organisms so food keeps for longer
radiotherapy
What are the dangers of Gamma?
They have a high penetrating power causing mutations in genes that can lead to cancer.
A small dose can cause cells to become cancerous and a large dose can kill cancer cells.
What are the benefits of analogue signals?
when the signal is amplified so too is the noise which weakens the clarity of the signal
if signals have a similar frequency they interfere with each other and it is difficult to distinguish each signal
Quantisation (when a continuous range is rounded) can give rise to a loss of lots of INFO
wider range of frequencies are needed to broadcast an analogue signal
What are the benefits of digital signals?
regeneration of signal is clear and exact as noise is ignored easily
Many signals can be transmitted at once with one cable
Quantisation doesn’t lose any information so more info can be transmitter in smaller space without any COMPROMISE on the quality of the signal
More programmes can be broadcast over the same frequencies
Digital systems are easier to design and build
Digital systems deal with easy to process data
Can be handled by microprocessors
Wider bandwidth so the response is clearer yet the noise is lower
Carries more info than analogue because the generator can switch between two values quickly in short space of time compared to analogue where the values are so wide ranging it takes longer to generate
Why can digital signals carry more info?
They can also squeeze in more programmes, because digital signals can carry more information per second than analogue signals.
When quantisation occurs less info is lost therefore more info is carried. Also they have a large bandwidth.
What is an analogue signal?
Analogue signals can vary in frequency, amplitude or both continuously.
What are digital signals?
Digital signals are a series of pulses consisting of just two states, ON (1) or OFF (0). There are no values in between.
Explain the meaning of the critical angle
When light travels from one medium to another it is refracted; it changes angle due to change in density.
Past a certain angle the light will simply be refracted back into the medium it is in, this angle is the critical angle.
What is light?
a transverse wave
What are the characteristics of images in a plane mirror?
image is as far behind as the object is in front
virtual
same size
laterally inverted
What is refraction?
when a ray of light travels from air into glass or water it slows down as it crosses the boundary between the two media.
This change in speed may cause the ray to change direction; refract.
What is the formula for refractive index?
n = sin i / sin r
n = speed of light in a vacuum / speed of light in material
What happens when the angle of incidence is less than the Ac?
A ray of light is refracted as it passes from a more dense medium to less dense one, but a small ray of light is also reflected.
What happens when the angle of incidence is equal to the Ac?
The light is refracted at 90 degrees to the normal and there is also a small reflected ray
What happens when the angle of i is more than the Ac?
TOTAL INTERNAL REFLECTION; light reflected back into the denser medium…no refraction occurs
What is the formula for the c?
sin c = 1/n
What can ruin the clear image in a plane mirror?
Several faint images form around the main image due to partial internal reflections at the non-silvered glass surface of the mirror
How are these extra faint images removed from the mirror?
When high quality images are required prisms are used to alter the direction of light rather than mirrors.
Where are prisms used?
bicycle reflectors and binoculars
What is an optical fibre made of?
an outer cladding of less optically dense glass and an inner core of optically dense glass
How is TIR achieved?
The fibres are very narrow so light entering the inner core always strikes the boundary of the two glasses at an angle greater than the Ac.
No light escapes b/c all is Reflected.
What are large numbers of OP.FIBRES called?
bundle
What is done to bundles?
tapered to produce a magnified image
How does an endoscope work?
Light travels down one bundle and illuminates object to be viewed
Light that is reflected by the object travels up a second bundle of fibres
an image of the object is created by the eyepiece
How are optical fibres used in modern telecommunications?
Electrical signals from telephone converted to light pulses by tiny lasers
The light pulses are sent into the ends of an op.fibres
Light sensitive detector at the other end changes the pulses back to electrical signals
These then flow into the telephone receiver; earpiece
What happens when white light passes through a prism?
it emerges as a band of colours; spectrum
Why is a spectrum formed?
White light is a mixture of colours and each colour travels through at a different speed so each colour is refracted by a different angle.
What is dispersion?
When each different colour of the spectrum emerges from the prism travelling in a different direction b/c each colour is refracted by a differing amount
Why does red light disperse the least?
The smaller the wavelength of the passing light, the greater is the refractive index observed. Therefore because red has the longest wavelength is deviates the least.
The deviation depends directly on the refractive index. As white light passes through prism, violet, the minimum wavelength, observes maximum refractive index for the prism and since deviation depends directly on the ref index, the violet wavelength gets deviated to the maximum extent.
How do we hear sounds?
These vibrations (compressions and rarefactions) of air particles reach our ears and cause the eardrum to vibrate. The vibrations are converted to electrical signal which are detected by the brain.
What can be done to sound waves?
What are sound waves?
Sound waves are longitudinal waves
How are sound waves produced?
by objects vibrating
How does a speaker cone create a sound?
As the cone moves L and R it pushes air molecules close together; COMPRESSION.
These particles push against neighbouring particles so that the compression appears to be moving right.
Behind the compression is a region where the particles are spread out; RAREFACTION.
By vibrating several times the cone has created a series of compressions and rarefactions travelling away from it. A LONGITUDINAL SOUND WAVE.
What can sound waves travel through best?
solids because there are more particles closer together to transmit the sound wave more quickly
Why can sound waves not travel in a vacuum?
there are no particles to carry the vibrations
Experiment to show that sound doesn’t travel in a vacuum?
Put a bell in a jar and ring it. We can see and hear the bell therefore light and sound travel in air. But when air is removed we can only see the bell so sound doesn’t travel in a vacuum.
Why is sound energy transferred much faster in liquids and solids?
the particles are much closer together meaning it is easier to transfer sound energy and more QUICKLY
How to measure speed of sound with echoes?
Stand 50m from a wall and clap your hands 20 times
An echo will be heard soon after each clap.
Time how long it takes for 20 echoes to be heard.
The sound altogether travelled 100m there and back 20 times
The speed is 2000 x the time measured!
How to measure sound speed with resonance tube?
Tuning fork produces vibrations and known frequency
The sound wave is reflected at the water boundary
If the tube is the right length (1/4 wavelength) the reflected wave will reinforce the original one giving a large amplitude and louder sound that can be heard.
RESONANCE
The first resonance is heard when the length of the air in the tube is 1/4 wavelength. When the sound is heard the length of air tube is measured and multiplied by 4 to get the full wavelength.
v = f x l
How to measure the speed of sound with an oscilloscope?
Set up simple generator, two microphones and an oscilloscope
Set generator to give sound of frequency 1 kHz
Start microphones close together and move apart until they are a complete wavelength away (trace on oscilloscope are exactly one above the other)
Measure the distance between the two microphones
Frequency can be found from the oscilloscope by doing 1/T
Speed is calculated by v = f x l
What is a reflected sound wave?
an echo
What is special when a sound waves strikes a surface?
the angle of incidence = angle of reflection
How does SONAR work?
Sound waved are emitted from the ship and travel to the seabed.
Equipment on the ship detects some of the sound waves that are reflected by the seabed.
The depth of the seabed can be calculated from the time between sending the sound wave and detecting the echo.
If fish are below the ship the reflected sound wave is distorted. Why are there two pulses of lower amplitude than the original?
The fish and seabed pulses have smaller amplitudes than the original because…
Not all of the pulse is reflected by the fish or the seabed.
Some ultrasound will be absorbed by the fish/water/seabed
Some ultrasound will be scattered and not return to the boat
Because reflection is taking place at different depths in the shed the sharp pulse becomes longer when it returns to the boat.
When is there optimum diffraction?
When the gap is near to the wavelength
What is a high pitch?
When the thing producing the sound vibrates quickly and so, produces sound waves with a high frequency.
What is a low pitch?
When the thing producing the sound vibrates slowly and so, produces sound waves with a low frequency.
What is frequency?
number of waves/second
What is frequency measured in?
Hz
What do the peaks and troughs represent on the CRO for sound waves?
peak = compression
trough = rarefaction
What is the audible range for humans?
20Hz to 20000 Hz
What is sound above and below the audible range?
ultrasound and infrasound
How is something shown to be loud on the CRO?
High amplitude
How is something shown to be quiet on the CRO?
Small amplitude
How is something made loud?
If the strings are struck hard lots of energy is transferred to them from whatever it has been struck with. The moves the particles even more from their equilibrium position and so we interpret the sound as louder.
Here the sound waves are transferring more energy.
How is something made quiet?
If it is struck gently the compressions created are less dense and less energy is transferred by the sound waves
What is ultrasound?
The frequency is above the human range (20,000 Hz)
What are medical uses of ultrasound?
pre-natal scanning
removal of kidney/gall stones
repair of damaged muscle/tissue
removing plaque from teeth
Describe the differences between ultrasound waves emitted by the transducer and those detected back at it
Reflected Waves:
lower frequency
longer wavelength
less intensity (amplitude decreased)
Describe the features of X rays and what happens when they enter the body
Description of an X-ray
X-rays are electromagnetic waves / part of the electromagnetic spectrum
X-rays are (very) high frequency (waves) through a vacuum at the speed of light
X-rays are (very) high energy (waves)
X-rays have a (very) short wavelength
Wavelength (of X-rays) is of a similar size to (the diameter of) an atom
X-rays are a transverse wave - oscillations / vibrations are
perpendicular to direction of energy transfer
X-rays are ionising radiation
Statement(s) as to what happens to X-rays inside the human body:
X-rays are absorbed by bone
X-rays travel through / are transmitted by tissue / skin
Describe the features of ultrasound and what happens when it enters the body
Description of ultrasound
ultrasound has a frequency above 20 000 (hertz) so therefore beyond the human (upper) limit (of hearing)
ultrasound is a longitudinal wave – oscillations / vibrations (of
particles) are parallel to direction of energy transfer
Statement as to what happens to ultrasound inside body:
ultrasound is (partially) reflected at / when it meets a boundary between two different media
travel at different speeds through different media
Statement as to what happens to ultrasound inside body:
ultrasound is (partially) reflected at / when it meets a boundary between two different media
travel at different speeds through different media
Why are X rays dangerous to use for prenatal scanning?
Ionizing
Damage cells/DNA/chromosome and nucleus
Cause mutations
Kill cells
Produce abnormal growth and so make cells cancerous
Why can astronauts not hear from outside their space suits?
Sound cannot travel through a vacuum as there is no medium in which vibrations can be set up and no particles to vibrate
Why does sound reflected at a boundary decrease when metal is changed to glass?
Less sound is reflected
Some sound is absorbed by/passes through glass
If the wavefronts are short, what colour will it appear as?
blue
If the wavefronts are long, what colour will it appear as?
red
What is the period of a wave?
the time it takes for one complete wave to pass a point
define a wave:
the transfer of energy without transferring matter
what is the same for all waves on the electromagnetic spectrum?
travel at the same speed through a vacuum
what is the range for human hearing?
20-20,000 Hz
name the waves on the EM spectrum in order:
radio, micro, infra red, visible, ultraviolet, x rays, gamma rays
What is a use of radio waves?
broadcasting and communication
what is a use of microwaves?
cooking and satellite communication
what is a danger of microwaves?
internal heating of tissue
what is a use of infra red?
heating, thermal imaging
what is a danger of infra red?
skin burns
what is a use of visible light?
photography
what is a use of ultraviolet?
fluorescence
what is a danger or UV?
blindness, damage to surface skin cells
what is a danger of x rays?
cancer + mutations
What is a transverse wave?
A wave whose oscillations are perpendicular to to the direction of the wave’s propagation
What is a longitudinal wave?
A wave whose oscillations are parallel to the direction of the wave’s propagation
Name an example of a transverse wave
Water wave; light wave; EM radiation
Name an example of a longitudinal wave
Sound waves
Define amplitude
The maximum displacement of a wave from its rest (undisturbed) position
Define frequency
The number of oscillations per second
Define wavelength (λ)
The distance (in metres) between the same points in an oscillation and the next (e.g. between two crests)
Define the period of a wave
The time taken for one oscillation
What do waves do?
Transfer energy and information without transferring matter
wave speed =
v=fλ
List all of the waves in the electromagnetic spectrum
Radio waves; Microwave; Infra red; Visible light; Ultra-violet; X-Rays; γ-Rays
What are uses of radio waves?
Broadcasting; communication
What are uses of microwaves?
Cooking food and satellite transmissions
What are uses of infra red waves?
Heating and night vision equipment
What are uses of visible light?
Optical fibres and photography
What are uses of ultra violet rays?
Fluorescent lamps
What are uses of X-Rays?
Internal imaging; medical scans
What are uses of γ-Rays?
Sterilising food and medical equipment
What are dangers of microwaves?
Internal heating of cells
What are dangers of infra red waves?
Burning skin
What are dangers of UV rays?
Blinding; damage to surface cells
What are dangers of γ-Rays?
Cancer; mutations
What type of waves are EM rays?
Transverse waves
What is the law of reflection?
angle of incidence = angle of reflection
Refractive index =
n = sin i/sin r
What is total internal reflection (TIR)
When all of the light from an incident ray is reflected back inside the original medium; when the angle of INCIDENCE is GREATER than the CRITICAL angle; when a light ray moves from an optically denser to less dense material
What is the critical angle?
The angle of incidence where the angle of refraction = 90°; the angle of incidence at which all light is totally internally reflected
sin C
sin C = 1/n
What type of waves are sound waves?
Longitudinal
What is the human frequency for hearing?
20 Hz to 20 kHz (20000 Hz)
An ambulance is producing sound represented by wave 2
Which wave would represent the sound an observer would hear as the ambulance approached them?
Wave 3.
The frequency of the sound would increase and wavelength decrease as the ambulance approached the observer.
What is the use of UV radiation?
produced by tanning bed lights to tan skin
used to detect conterfeit money
used to clean water
Give three properties (features) common to all EM waves
They all…
travel at the speed of light
all transverse waves
all transfer energy and information without transferring matter
all travel through a vacuum
Which wave has the largest wavelength?
wave 1
largest distance between adjacent crests
How can you make a transverse wave with a slinky?
Move your hand in a side to side movement
List the EM spectrum in order of decreasing frequency
Gamma
X-ray
UV
Visible
IR
Microwave
Radio
What is blueshift in terms of movement of stars or galaxies?
If a star is moving towards the observer, the wavelength of the light it is producing is squashed.
The observer sees light of a smaller wavelength and higher frequency- it is a different colour as it is shifted towards the blue end of the spectrum
What is redshift in terms of movement of stars or galaxies?
If a star is moving away from the observer, the wavelength of the light it is producing is stretched.
The observer sees light of a larger wavelength and lower frequency- it is a different colour as it is shifted towards the red end of the spectrum
How is wavespeed, wavelength and frequency related?
wavespeed = wavelength x frequency
v = velocity
f= frequency
λ = wavelength
Label the compressions, rarefactions and wavelength on the longitudinal wave below
.
What is 204 nm in m?
204 x 10-9 m
0.000 000 204 m
What is the Doppler effect?
When there is a change in frequency (wavelength) of sound (or light) an object is producing as a result of it moving away or towards an observer.
How can you make a longitudinal wave with a slinky?
move your hand in a forwards and backwards movement
Sketch a graph of how frequency varies with time as an object approaches an observer, passes them and then travels away from them.
.
How would you measure the frequency of waves passing a jetty?
Time how long it take for 10 waves to pass the end of the jetty
frequency = 10 waves / time for 10 waves to pass
An ambulance is producing sound represented by wave 2
Which wave would represent the sound an observer would hear as the ambulance travelled away from them?
Wave 1.
The frequency of the sound would decrease and wavelength increase as the ambulance moves away from the observer.
Fred noticed that 10 waves passed a point in 5 seconds. What is the frequency of the wave?
frequency = 10 waves/ 5 s
= 2 Hz
What is 700 micrometres in metres?
700 x 10-6 m
0.0007 m
What is a wavefront?
A wavefront connects all points on a wave which are moving in phase
Fred noticed that 10 waves passed a point in 5 seconds. What is the period of the wave?
Time period = 5 seconds / 10 waves
= 0.5 seconds for one wave to pass
Which wave has the largest amplitude?
wave 2
It has the largest displacement from the equilibrium
What is the unit for time period?
seconds or s
What is the unit for amplitude?
metres (m) or decibels(dB)
What has a larger wavelength?
Infrared or gamma?
Infrared
Match the following terms with their definition
Frequency
How far a wave travels in one second
Wavelength
The number of waves going past in one second
Wave speed
The length of one repeat of the wave pattern
frequency- the number of waves going past in one second
wavelength- the length of one repeat of the wave pattern
wave speed- how far a wave travels in one second
Why are UV waves dangerous?
They can damage the retina and damage eye sight
They can cause skin cancer
What is the use of microwaves?
produced by microwaves to cook food
produced by mobile phones to communicate
Produced by satellites to send signals to satellite dishes
What is a transverse wave?
Where the oscillation is 90° to the direction of wave travel
How do the waves of red light differ from waves of violet light
ROY G BIV
Red light-larger wavelength and lowe frequency- it has less energy
Blue light- smaller wavlength and higher frequency- it has more energy
What are the uses of infrared radiation (IR)
emitted by ovens to cook food
emitted by radiators to heat houses
emitted by tv controllers to control t.v.
What is the relationship between wavelength and frequency of a wave?
As wavelength increases, frequency decreases
They are inversely proportional
What is the use of X-rays?
Used to detect breaks in bones
used to detect crystal structure in salts
List the EM spectrum in order of increasing frequency
Radio
Microwave
IR
Visible
UV
X-ray
Gamma
What is 13 kHz in Hz?
13 x 103 Hz
13 000 Hz
Fred noticed that 10 waves passed a point in 5 seconds. The waves are 4 metres apart. What is the speed of the wave?
frequency = 10 waves/ 5 s
= 2 Hz
wavespeed = frequency x wavelength
= 2 Hz x 4 m
= 8 m/s
What is the relationship between time period and frequency?
time period = 1 / frequency
or
frequency = 1 / time period
List the EM spectrum in order of decreasing wavelength
Radio
Microwave
IR
Visible
UV
X-ray
Gamma
How is gamma radiation dangerous?
It can cause mutations in cells- cancer
How are X-rays dangerous?
They can cause mutations of cells- cancer
Which parts of the EM spectrum is considered to be dangerous?
UV
X-ray
Gamma
Label the wavelength, amplitude, crest and trough of the transverse wave below
.
How is infrared dangerous?
It can cause skin burns if too hot
What is a longitudinal wave?
Where the oscillation is along the direction of wave travel.
Give three examples of a longitudinal wave
sound
shock wave
P wave
What are the uses of radio waves?
radio signal for radio
radar
walkie talkie signals
t.v. signals
What are the uses of gamma radiation?
Used to kill cancer tumours
used to sterilise medical equipment
emitted by radioisotope tracers to detect cancer in the body
How do you calculate the frequency of a water wave?
frequency = number of waves/ time for those waves to pass a pointfrequency = number of waves/ time for those waves to pass a point
If a star is moving very quickly away from an observer it is possible that the light can no longer be observed with the naked eye. Explain.
The light’s wavelength is shifted so far to the red end of the spectrum that its wavelength is the same as infrared light and is invisible to the naked eye.
What does monochromatic mean?
Light of a single wavelength or colour.
What is 100 MHz in Hz?
100 x 10^6 Hz
100 000 000 Hz
What is the unit for wavelength?
metre or m
Give three examples of a transverse wave
water wave
any EM wave
S wave
List the EM spectrum in order of increasing wavelength
Gamma
X-ray
UV
Visible
IR
Microwave
Radio
Which wave has the highest frequency?
wave 3
it has more waves per second
The frequency of the ticker timer is 50 Hz. What is the time between two dots it prints?
time period = 1 / frequency
time period = 1 / 50
= 0.02 seconds
How are all the EM radiation different?
They have….
different wavelengths
different frequencies
therefore they have different uses and dangers
What is the unit for wavespeed?
metre per second or m/s
Galaxies rotate
If one side of the galaxy is moving toward us and one side is moving away from us, what would we observe in terms of the light we receive from each side of the galaxy?
Side moving towards us will be blueshifted, the light will have a smaller wavelength and higher frequency- shifted towards the blue end of the spectrum
Side moving away from us will be redshifted, the light will have a large wavelength and lower frequency- shifted towards the red end of the spectrum
What is the use of visible light?
produced by light bulbs to see things
produced by bioluminescent creature to attract prey
What is the unit for frequency?
Hertz or Hz
How is sound created?
sound is created by vibrations
List some properties of sound
it is a lonitudinal wave
it is created by a vibration
it cannot travel through a vacuum
it can travel through a solid, liquid or gas
it can have different frequencies or pitch
it can be reflected and diffracted
How does speed of sound in air relate to temperature? Explain
As temperature of air increases, speed of sound decreases.
Particles in warm air are more spread out and collisions between particles are more difficult
Sound is a series of compressions and rarefactions.
How does the speed of sound compared in a solid, liquid and gas? Explain
Sound travel faster through a solid than a liquid and gas.
Sound is a vibration which is transferred from particle to particle via collisions.
Solid particles are closer together and have stronger forces between them- vibrations are passes between particles more quickly
How can speed of sound through air be measured in a laboratory?
connect two microphones to a microsecond timer
place the two microphones 2.00 metres apart using two metre rules
place padding under each microphone to prevent sound travelling through the table
create a sharp sound behind the first microphone
record the time it takes for the sound to travel from microphone 1 to microphone 2
repeat five times and calculate the mean time
calculate the speed of sound through air by
s = 2.00 m / mean time
How can speed of sound through a lab bench be measured in a laboratory?
connect two microphones to a microsecond timer
place the two microphones face down on a lab bench 2.00 metres apart using two metre rules
create a sharp tap to the lab bench behind the first microphone
record the time it takes for the sound to travel from microphone 1 to microphone 2
repeat five times and calculate the mean time
calculate the speed of sound through air by
s = 2.00 m / mean time
How can speed of sound through air be measured in the playground?
stand exactly 50.00 metres from a large wall of a building
strike two metal bars repeatedly until a ryhthm is set up and the metal bar is being hit together at the same time the echoes returns.
start the stopwatch on one strike and time 20 complete strikes.
This time is how long it take the sound to travel to and from the wall 20 times or 100.00 x 20 = 2000 m
speed of sound is s = 2000 m / time
Speed of sound can be measured accurately using a stopwatch.
If a starting pistol is used, the people timing must start the stopwatch when they see the smoke from the pistol and then stop it when they hear the sound.
How can you ensure that the speed of sound is measured accurately and what assumption is made?
very large distances must be used as human reaction time introduces large uncertainties in time measurements
The assumption is that the light reaches the person immediately.
The position of imperfections in a metal can be located using ultrasound.
An ultrasound pulse is sent into the metal and reflections received. If the speed of sound in the metal is 5000 m/s and the echo received 20 microseconds later.
How can the distance to the imperfection be calculated?
20 microseconds = 0.00002 s
divide time by 2
time to imperfection = 0.00002 s / 2 = 0.00001 s
d = s x t
distance = 5000 m/s x 0.00001 s = 0.05 m or 5 cm
Bats locate their prey by echosounding.
They use pulses of ultrasound and listen for the echo with their large ears. If the time between the pulse and echo is small, the insect is closer to the bat.
Name another animal which uses echo sounding.
dolphins
When calculating the distance in an echosounding question, what is the most common error?
The distance calculated from the speed of sound and time for echo must be divided by two!
What is the human hearing range?
20 - 20 000 Hz
What is ultrasound?
Any sound over 20 000 Hz
Ultrasound is used to image babies in the womb.
An image is formed on the screen if reflections are received from the different surfaces (layers) of the baby.
How does the time for the reflection relate to the distance to the surface?
The further the surface is from the ultrasound transmitter/receiver, the longer it takes for the echo to return.
The distance to a storm can be calculated using the lightning seen and the thunder heard.
What assumption is made in this calculation?
Lightning makes thunder. Flash is seen instantly.
0 seconds
What is the amplitude of a sound wave measured in?
decibels
Loudness or volume
If low frequency is low pitch sound.
What is high frequency sound?
High frequency = high pitch
As the pitch of sound increases, what happens to the distance between the compressions?
distance between compressions decreases
What property of ultrasound allows it to be used for cleaning?
Ultrasound is a vibration, the vibrations loosen dirt in hard to reach areas.
What property of ultrasound allows it to be used to break up kidney stones?
Concentrated beams of ultrasound are absorbed by the kidney stone, vibrations occur in the kidney stone and this breaks it up into small pieces.
What type of wave is sound?
Longitudinal
vibrations are parallel to direction of wave travel
