Section 2 - Waves and the Electromagnetic Spectrum Flashcards
What happens when a wave travels through a medium?
The particles of the medium vibrate and transfer energy and information between each other
What do waves transfer?
Energy and information
What doesn’t change when a wave travels through a medium?
The particles location
What is the amplitude of a wave?
The displacement from the rest position to a crest or trough
What is the wavelength of a wave?
The length of a full cycle of the wave
What is the frequency of a wave?
The number of complete cycles of the wave passing a certain point per second
What is the period of a wave?
The number of seconds per cycle
What is the relationship between frequency and the period of a wave?
They are inverse
What is the period equation?
Period = 1 / Frequency
What direction vibrations do transverse waves have?
Perpdenciular to the direction the wave travels
Give examples of transverse waves
EM Waves
S Waves
Ripples and waves in water
What direction vibrations do longitudinal waves have?
Parallel to the direction the wave travels
Give examples of logitudinal waves
Sound Waves
P Waves
What are the compressions in longitudinal waves
The squashed up areas of the wave (high pressure with lots of particles)
What are the rarefactions in longitudinal waves?
The stretched out areas of the wave (lower pressure with fewer particles)
What is the equations for wave speed?
V = F x λ m/s = Hz x m
V = x / t m/s = m / s
A wave has a speed of 0.15 m/s and a wavelength of 7.5 cm
Calculate it’s frequency
cm -> m
7.5/100= 0.075
v / λ = f
0.15 / 0.075 = f
2 Hz
What can you use to measure the speed of sound?
An oscilloscope
To measure the speed of sound what apparatus do you need?
A signal generator
Speaker that can generate sounds with a specific frequency
Two microphones
An oscilloscope
How do you setup the oscilloscope when measuring the speed of sound?
So the detected waves at each microphone are shown as separate waves
What do you do with the microphones when measuring the speed of sound?
Slowly move one away until the two wavess are aligned but have moved one wavelength apart
When measuring the speed of sound, what is one wave length equal to?
The distance between the microphones
When measuring the speed of sound, state all the measurements you need at how you get them?
Frequency - the frequency you set the frequency to on the speaker
Wavelength - the distance between the microphones, once they match up on the oscilloscope with one being one wavelength ahead
What do you use to measure the speed of water ripples?
A strobe light
Signal genertor
Ripple tank with a dipper
What do you do with the strobe light when measuring the speed of water ripples?
Alter the strobe lights’ frequency until it matches the ripples’ frequency
How do you tell the frequency of the strobe light and the ripples are the same?
The wave pattern on the screen will appear to freeze and stop moving
Why does what happens when the frequency of the strobe light and the ripples are the same happen?
The light lights up the waves at the same point in there cycle each time
When measuring the speed of water ripple what measurements must you have and how do you get them?
Frequency - The frequency you set tthe dipper to
Wavelength - Measure the wavelength of 10 lines apart and then find the average wavelength
What method do you use to find the speed of waves in solids?
Peak Frequency
When measuring the speed of waves in solids, what measurements must you take before hand?
The length of a metal rod
Tap the ___ with the ______
Tap the rod with the hammer
What does tapping the rod with a hammer give you?
The peak frequency
How many times should you repeat the peak frequency method?
Three times
How do you calculate the speed of a wave in solids?
Using v = fλ
λ is equal to twice the length of the rod
What is λ equal to when finding the speed of waves in solids?
Twice the length of the rod
λ is equal to ____ the length of the rod
λ is equal to twice the length of the rod
Describe an experiment to measure the wavelength of a water wave
Add water to a ripple tank with a signal generator
Set strobe light to frequency of dipper, you can tell when they’re in sync when the waves don’t appear to move
Measure the wavelength of 10 waves and then calculate and average
Times that by the frequency of the dipper to calculate wave speed
What can happen to waves when they meet boundaries?
Reflected
Absorbed
Transmitted
How do you remember what happens to waves when they meet boundaries?
R.A.T (Toby)
What happens when a wave us absorbed?
The wave transfers energy to the materials energy stores
What happens when a wave is transmitted?
The wave carries on travelling through the new material
What does wave transmission lead to?
Refraction
What is refraction used in?
Communications
Glasses
Cameras
What happens when a wave is reflected?
The wave is neither absorbed or transmitted instead it is sent back away from the second material
What is an example of a wave being reflected?
An echo
What is refraction?
Waves changing directions at a boundary
Waves travel at _______ speeds in materials with ______________
Waves travel at different speeds in materials with different densities
When does refraction not occur?
When a wave travels along the normal or when the densities of the two mediums are the same
The _______ the change in speed, the more a wave bends
The greater the change in speed, the more a wave bends
Compare the speed of EM waves in a vaccum to a denser material
EM waves travel slower in denser materials
What affects how much an EM wave refracts?
Wavelength
How does wavelength affect refraction?
The shorter the wavelegnth, the more the wave bends
What stays the same as the wave passes the boundary?
It’s frequency
In terms of refraction, what is the relationship between wavelength and velocity?
As wavelength decreases, velocity decreases
As wavelength increases, velocity increases
What is the name of the ray that meets the normal at the boundary?
The incident ray
What is the angle of incidence?
The angle between the incident ray and the normal
What will happen to a light wave if it passes from a less dense to a more dense medium?
It will move towards the normal
What will happen to a light wave if it passes from a more dense to a less dense medium?
It will move away from the normal
Give an example of a low density medium
Air
Give an example of a high density medium
Glass
If a wave speeds up when it passes through a medium where does it bend to?
Away from the normal
If a wave slows down when it passes through a medium where does it bend to?
Towards the medium
How does Izak remember what happens with the speed of a wave and refraction?
Like a graviational pull, if you go fast enough you can escape if you don’t you get pulled in
A light ray enters air from water at 50* to the nrmal
How does it bend relative to the normal?
Away from the normal as gains speed
What are sound waves caused by?
Vibrating objects
What are the sound vibrations passed thorugh as?
A series of compressions and rarefactions
What determines which frequencies and object can transmit?
Size
Shape
Structure
Compare the speeds of speed in the different states?
Fastest in solid, medium in liquid and slowest in gas
What doesn’t change when a wave pases from one medium to another?
Frequency
What are reflected sound waves called?
Echoes
What type of objects cause sound waves to reflect?
Hard and flat
When do you hear sound?
When the ear drum vibrates
List the path sound takes in the ear
Outside Ear -> Eardrum -> Ossicles -> Semicircular Canals -> Cochlea -> Brain
What is the role of the eardrum in the ear?
To vibrate the sound into the ear
What are the name of the tiny bones in your ear?
The ossicles
What turns the sound into the electrical signals which is then sent to the brain?
The cochlea
What is the electrical signals for sound sent along?
The auditory nerve
What determines the pitch of a sound?
It’s frequency
What determines the volume of a sound?
It’s amplitude
What limits human hearing?
The size and shape of the eardrum
The structure of all the parts within the ear that vibrate to transmit the sound wave
Describe how you hear a sound wave
The sound enters the ear and vibrates the ear drum, which then vibrates the ossicles then the semicircular canals and then the cochlea
The cochlea then converts the sound to electrical signals which is sent along the auditory nerve to the brain
What happens to ultrasound waves when they hit boundaries?
They get partially reflected
What is partial reflection?
When a wave crosses a medium and some of the wave is reflected off the boundary whilst some is transmitted
What hertz is ultrasound?
Any frequency higher than 20,000 Hz
How is ultrasound useful?
Medical imaging
Industrial imaging
Sonar
How is ultrasound used for medical imaging?
Ultrasound is passed through the body but bounces of certain materials
A computer processes this infomation and produces a video image
How is ultrasound used for industrial imaging?
Ultrasound is used to find flaws in objects as they will enter the material and will usually be reflected by the far side of the material
However, if there is a flaw it will be reflected sooner
What is sonar used for?
To find out the deepness of the water and to locate objects in deep water
A pulse of ultrasound takes 4.5 seconds to travel from a submarine to the sea bed and back again
If the speed in sea water is 1520 m/s, how far away is the submarine from the seabed?
S = 2D / T 2D = S x T 2D = 6840 m D = 3420 m
What is infrasound?
Sound with frequencies lower than 20 Hz
What are examples of natural uses of infrasound?
Animal communication (eg. Elephants and Whales) Natural Disasters (eg. Volcanoes, Earthquakes and Avalanches)
How do scientists predict natural events?
Because these events produce infrasound
Scientists can monitor infrasound to predict it
What happens when seismic waves reach a boundary between different layers of material?
They are absorbed or refracted
What type of seismic wave can travel through the Earth’s core?
P-waves
What type of seismic wave can’t travel through the Earth’s core?
S-waves
What have scientists been able to work by observing seismic waves?
The internal structure of the Earth
The size and material of the Earths’ inner layers
What type of waves are P-waves?
Longitudinal
What types of state can P-waves travel through
Solids and liquids
Compare the speed of P-waves to S-waves
P-waves are much faster
What type of waves are S-waves
Transverse waves
What types of state can S-waves travel through?
Solid
Which seismic wave is transverse?
S-waves
Which seismic wave is longitudinal?
P-waves
Which seismic wave is faster?
P-waves
How do you remember which is the fastest seismic wave?
Primary means earliest in time meaning it is the first to get there which means it’s the fastest
How do you remember which seismic wave is transverse or longitudinal?
S is next to T in the alphabet and S-waves are Transverse
How do you remember which seismic wave travels through which state of material?
S-waves travel through solids, S for solid
Primary do everything
S-waves produced at the Earth’s North Pole would not be detected at the South Pole
Suggest one conclusion you can make about the Earth’s core from the observation
Explain your answer
S-waves can only travel through solids
S-waves can’t travel through the core, meaning atleast a bit of the core is liquid
What is the law of reflection?
Angle of incidence = Angle of reflection
What is the angle of incidence?
The angle between the incoming wave and the normal
What is the incident ray?
The incoming ray
What is the angle of reflection?
The angle between the reflected wave and the normal
What is the reflected ray?
The ray that is reflected off the boundary
What is the normal?
An imaginary line that’s perpendicular to the surface at the point of incidence
What does TIR depend on?
The critical angle of the material
What is the critical angle of a material?
The angle at which the angle of refraction is 90* (perpendicular to the normal)
When does TIR happen?
When the angle a wave hits a less dense medium is greater than the critcal angle
What is TIR?
Total reflection of wave from a more dense medium to a less dense medium with no wave coming out instead it all internally reflects
Reflection can be _______ or _____
Reflection can be specular or diffuse
When does specular reflection occur?
When waves are reflected in a single drection by a smooth surface
When does diffuse reflection occur?
When waves are reflected by a rough surface
Why does diffuse reflection occur?
Because the normal is different for each incident ray meaning the reflection angle is different (angle of incidence = angle of reflection)
Name the type of reflection that occurs when waves are reflected by a smooth mirror
Specular
A light ray is incident on a mirror at an angle of 30*
What will it’s total angle be?
Reflection angle = 30* ∴ ∠Reflection + ∠Incidence = Total Angle 30 + 30 = 60* 60*
When investigating refraction, why should a thin beam of light be used?
So you can easily trace the ray to measure the angle between the ray and the angle
What does the colour and transparency of light depend on?
It’s wavelength
What are opaque objects?
Objects which do not transmit light
What do white objects do?
Reflect all wavelengths of light equally
What do black objects do?
Absorb all wavelengths of light
What type of objects transmit light?
Transparent/translucent objects
What do colour filters do?
Only let through particular wavelengths
If a red object was placed in front of a blue filter what colour would the object appear?
Black
Explain why a cucumber looks green?
Because it reflects green light but absorbs all other wavelengths of light
Give the two types of lens’s
Converging (Convex)
Diverging (Concave)
Describe a converging lens?
Bulges outwards in the middle
What does a converging lens do to light?
Converges it at the principal focus
Describe a diverging lens?
Caves inwards
What does a diverging len do to light?
Spreads it out
What is the principal focus of a converging lens?
The area where the rays parallel to the axis meet
What is the principal focus of the diverging lens?
The area where the rays parallel to the axis appear
How do you find the principal focus of a diverging lens?
Trace them back until they all appear to meet up at a point behind the lens
What is the focal length?
The distance from the centre of the lens to the principal focus
What is the unit for principal focus?
F
When is an image formed?
When all light rays from a certain point on an object appear to come together
Give the two types of images?
Real
Virtual
When is a real image formed?
When lights rays actually come together to form the image
What type of image can be put onto a screen?
A real image
What type of image is found on the eye’s retina?
Real
When is a virtual image formed?
When light rays from the object appear to be coming from a completely different place to where they’re actually coming from
What type of image can’t be put onto a screen?
Virtual
Give an example of an object which creates virtual images?
A magnifying glass
What increases the power of a lens?
Its curvature
Describe the relationship between power of lens and focal length
The more powerful the lens, the more strongly it converges rays of light, so the shorter the focal length
What lens has a positive power?
Converging
What lens has a negative power?
Diverging
How can you increase the power of a lens?
Change the material
Increase it’s curvature
What is the principal focus of a converging lens?
The point where rays hitting the lens parallel to the axis meet
What is the principal focus of a diverging lens?
The point where light rays hitting the lens parallel to the axis appear to come from
Describe the image produced from a diverging lens
Virtual
Right way up
Smaller
Same side of the lens
Briefly describe how to draw a ray diagram of a diverging lens?
Draw two rays, one from the object through the lens and the other parallel to the axis of the lens through the lens
Refract the line that went through the lens, that is parallel to the lens
Draw dotted line from 1F to refraced ray
The point where all three lines intersect is where the image is formed
What affects the image produced from a converging lens
Its distance from the object
Briefly describe how to draw a ray diagram of a converging lens?
Draw two rays, one from the object through the lens and the other parallel to the axis of the lens through the lens
Refract the line through 1F
The image will form when the refracted ray meets the ray that went straight through the lens
How will the object appear when 2F away from a converging lens?
Same size 2F away inverted Real Other side of the lens
How will the object appear when 1F-2F away from a converging lens?
Real
Inverted
Bigger
Beyond 2F
How will the object appear when <1F away from a converging lens?
Virtual
Right way up
Bigger
Same side of the lens
On a ray diagram, what determines whether the image is upright?
If its above the axis
On a ray diagram, what determines whether the image is inverted?
If its below the axis
On a ray diagram, what determines whether the image is real?
If the image is past the lens
On a ray diagram, what determines whether the image is virtual?
If the image is before the lens
What kind of image does a diverging lens produce?
Virtual
Compare the speeds of EM waves?
The same in a vacuum
But different in different materials
What do we group EM waves off?
Wavelength/frequency
How many EM waves are there?
7
Name all the EM waves
Radiowaves Microwaves Infrared Visible light Ultraviolet X-rays Gamma rays
What causes the generation of EM waves?
Changes in atoms and their nuclei
What creates gamma rays?
Changes in an atoms nucleus
What creates visible light?
Changes in an electrons energy level
What does the higher frequency mean of a wave?
The more energy it transfers
What EM wave transfers the most energy?
Gamma rays
Describe the interaction between the human body and radio waves
No harm as the waves are transmitted fully
Describe the interaction between the human body and microwaves
Some wavelengths can be absorbed, causing the heating of cells
What can some wavelenghts of microwaves do to the body?
Heat the cells
Describe the interaction between the human body and infrared
Mainly reflected but can be absorbed causing heating, which may cause burns if the skin gets too hot
Describe the interaction between the human body and visible light
Mainly reflected but can be absorbed causing heating
Describe the interaction between the human body and ultraviolet
Absorbed by the skin which can cause damages to cells and could lead to skin cancer
Why is ultraviolet much more dangerous than IR?
Because it has a higher frequency meaning its more ionising
What can UV cause to the human body?
Skin cancer
Eye conditions and blindness
Describe the interaction between the human body and x-rays
Absorbed which can cause mutations and damage cells
Describe the interaction between the human body and gamma rays
Absorbed which can cause mutations and damage cells
Explain why gamma rays are more dangerous to humans than visible light?
Gamma rays are ionising so they can cause tissue damage and cancer but visible light isn’t ionising
They carry more energy than visible light, so their potential for damage is higher
What does every object absorb and emit?
EM radiation
What does the distribution and intensity of wavelengths depend on?
The objects temperature
What is intensity?
The power per unit area
What happens to the object as the temperature increases?
The intensity of every emitted wavelength increases
Compare the intensity of different wavelengths emitted when the object is increased?
The shorter the wavelength the faster the intensity increases
Describe an object with constant temperature in terms of emission and absorption
Absorption = Emission
Describe an object that is heating up in terms of emission and absorption
Absorbing > Emitting
Describe an object that is cooling down in terms of emission and absorption
Emitting > Absorbing
Where does the Earth get most of its radiation from?
The Sun
What happens to the radiation the Sun gives to the Earth?
Some reflected
Most absorbed
What does the reflected radiation do to the Earth?
Reflect out to the Earth’s atmosphere,clouds and surface which will cause an increase in temperature
What happens to the absorbed radiation in the clouds/atmosphere?
Is emitted at night causing a decrease in the temperature
What type of surfaces are the best emitters?
Black
Briefly describe how to investigate how well different surfaces emit radiation?
Fill identical test tubes with hot water whilst surrounding them with different types/colours of materials (eg. Black, White, Glossy and Matte paper)
Measure the temperature, the one with the greatest temperature drop is the best emitter, the one with the lowest temperature drop is the best insulator
What will emit better: Shiny or matte surfaces?
Matte
What will emit better: White or black surfaces?
Black
Explain what is happening in terms of radiation and temperature when a bowl of ice cream is left on a counter in a warm room?
The bowl of icecream is absorbing more infrared radiation than it is radiating
This causes an increase in the temperature of the bowl of ice cream
What are EM waves made of?
Oscillating electric and magnetic fields
What make up oscillating charges?
Alternating currents (AC0
What happens when charges oscillate?
They produce oscillating electric and magnetic fields
The frequency of the waves produced will equal ________________
The frequency of the waves produced will equal the frequency of the alternating current
What is a transmitter, when making radio waves?
The object in which charges oscillate to create the radio waves
Describe how radio waves are converted into a current
A reciever absorbs radio waves
The energy carried by the waves transfers to the electrons in the matierla causes the electrons to oscillate, generating an alternating current
What are radio waves mainly used for?
Communication and broadcasting
What are the wavelengths of long-wave radio waves?
1-10km
What is the name for when a wave bends
Diffraction
Why can long-wave radio waves go halfway around the world?
Because they can diffract around the curved surface of the Earth
What are the wavelengths of short-wave radio waves?
10-100m
How do short-wave radio waves go across the world?
By being reflected by the Earth’s atmosphere
What type of wave does bluetooth use?
Short-wave radio waves
Describe the wavelength for TV and FM radio transmissions
Very short
What must waves, that are used for communication to and from satellites, be able to do?
Easily pass through the Earth’s watery atmosphere
Explain why signals between satellites are usually transmitted as microwaves
They can easily pass through the Earth’s watery atmosphere without being absorbed
How do microwaves work?
The microwaves transmit a few centimeters into the food before being absorbed and transferring the energy they are carrying to the water molecules, heating up the food
Describe the difference between microwaves in ovens and in satellites?
The ones with satellites must be able to pass through the atmosphere,. whereas, the microwaves in microwaves need to be absorbed by water molecules
Give uses of microwaves
Communication
Microwave ovens
What gives out infrared radiation?
All warm objects
Give uses of infrared radiation?
Burgular alarms Thermal imaging Short range communication Cooking Optical fibres
What do infrared cameras do?
Detects IR and converts it into an electrical signal which is displayed on a screen
How do infrared sensors work?
By detecting a change in infrared radiation and then sounding an alarm or a security light
How is infrared used for cooking?
Infrared causes objects to get hotter meaning adding IR to food will cause it to heat up
What are the disadvantages of using infrared to transfer information?
Must be a short distance
Must be in line of sight
What are optical fibres?
Thin glass or plastic fibres that carry data over long distances
What do optical fibres rely on?
Total Internal Reflection
Why do optical fibres use a single wavelength?
To prevent dispersion which can otherwise cause some information to be lost
Give three uses of infrared radiation
Any three from: Burgular alarms Thermal imaging Short range communication Cooking Optical fibres
What does photography rely on?
Visible light
What are uses of visible light?
Photography
How does photographic film work?
By reacting to light to form an image
How do digital cameras work?
By using image sensors to detect visible light and generate an electrical signal which is then converted into an image
What is ultraviolet used in?
Fluorescent lamps
Bank notes/passports
Security pens
Sterilising water
What is fluorescence?
A property of chemicals where UV radiation is absorbed and then visible light is emitted
How is UV used to sterilise water?
It’s blasted onto water killing any bacteria in it
What are x-rays used for?
To view the internal structure of objects and materials
How do radiographers take x-ray images?
The patient is placed on a detector plate whilst x-rays are directed onto the body, the x-rays transmit through the flesh and are absorbed by denser material (eg. Bones and Metal) meaning the image will pick up areas of high x-ray amount meaning low density material (eg Flesh) and areas of low x-ray amount meaning high density material (Eg. Bones and Metal)
What are gamma rays used for?
Sterilisation
Medical imaging
Cancer treatments
How are gamma rays used in sterilisation?
They kill microbes
What are the benefits of using gamma rays to steralise food?
No need to freeze it, cook it or preserve it some other way
Give examples of gamma being used in medical imaging?
PET scans and tracers
How are gamma rays used in cancer treatments?
Targeted at cancer cells to kill them
What are the cons of using gamma radiation for cancer treatment?
If not aimed correctly will cause damage to healthy cells
State two uses of ultraviolet radiation?
Any two from: Fluorescent lamps Security pens Detecting forged bank notes Sterilising water
Suggest one advantage of sterilising food with gamma rays
You don’t have to freeze it/cook it/preserve it to keep it fresher for longer
What is the amplitude of a wave?
The displacement from the rest position to a crest or trough
What is the wavelength of a wave?
The length of a full cycle of the wave
What is the frequency of a wave?
The number of complete cycles per second
What is the period of a wave?
The number of seconds it takes for one full cycle
Describe the difference between transverse and longitudinal waves?
In longitudinal waves, the vibrations are parallel to the direction of wave travel.
In transverse waves, the vibrations are at right angles to the direction of wave travel.
What affects an objects ability to transmit given frequencies of sound?
It’s size, shape and structure
What is the frequency of ultrasound?
> 20,000 Hz
What is the frequency of infrasound?
> 20 Hz
What conditions are needed for total internal reflection to occur?
The light must be travelling from a more dense medium into a less dense medium (eg. glass to air)
The angle of incidence must be greater than the critical angle.
Explain what happens to white light that hits a white object?
All of the light is reflected by the object
True or False? Diverging lenses always produce real images?
False
True or false? All EM waves are transverse?
True
Give one danger of UV radiation?
Any one from:
Skin cancer
Cataracts
Blindness
Give one danger of x-rays/gamma rays
Mutation of the genes
Describe the average power absorption and radiation for an object of constant temperature
Equal absorption and radiation
What kind of current is used to generate radio waves in an antenna?
Alternating current
