P5 - Waves in matter Flashcards
How is energy transferred by a wave?
Energy is transferred in direction wave is travelling without any transferring matter (particles stay in the same spot)
What is the amplitude?
The distance from the crest to the resting position.
What is the wavelength?
The lengths of one complete wave (eg from crest to crest)
What is the frequency?
The number of complete waves that pass a point in one second (Hz)
What is the period?
The number of seconds it takes for one complete wave to pass.
Equation for period?
Period = 1 / Frequency
What is a transverse wave?
The particles / oscillations vibrate perpendicular to the wave direction.
Examples of transverse waves?
1) All electromagnetic waves
2) Waves in water
3) Light (an electromagnetic wave)
4) S waves
Transverse waves and liquids:
These waves can travel on surface of a liquid but not through it.
What are longitudinal waves?
The particles / oscillations vibrate parallel to the direction of the wave direction.
Example of longitudinal waves?
1) Sound waves
2) P waves
Wave speed equation:
Wavespeed (m/s) = wavelength (m) x frequency (Hz)
or
Speed (m/s) = distance (m) / time (s)
How do you convert Kilohertz (KHz) and Megahertz (MHz) into Hertz (Hz)?
1 KHz = 1,000Hz (Multiply by 1,000)
1 MHz = 1,000,000 Hz (Multiply by 1,000,000)
Experiment to find speed of sound?
Do the OSCILLOSCOPE method:
1) Connect two microphones to a oscilloscope which will display the sound waves
2) Move one microphone away so that the waves on the oscilloscope are the same, but have moved one wavelength apart.
3) Measure the distance between the microphones (finding the wavelength)
4) Find frequency (whatever the signal generator was set to)
5) Use the wave speed =wavelength x frequency equation
Experiment to find the frequency?
- You will need a cork and stopwatch
1) Float cork in ripple tank and it should bob as wave passes
2) When cork is a top of bob start stopwatch
3) Count how many bobs in a set time
4) Divide by number of seconds timed to find bobs per second which is the waves per second (Frequency)
Experiment for wavelength?
- Record or take picture of waves from birds eye view in ripple tank.
- Measure the distance of multiple waves (eg 10) and divide by number of waves to find average wavelength (if 10 waves was 26 cm then 1 wave will have wavelength of 2.6 cm)
Experiment for measuring wave speed?
- Use large piece of paper, pencil and stopwatch
1) Place large piece of paper in front of ripple tank
2) As wave moves across tank, one person tracks the wave’s crest with pencil and straight line on the large piece of paper.
3) The second person should use stopwatch and time for a certain amount of time. When time is finished the first person should stop drawing.
4) Use equation speed = distance / time - Distance for line measurement
- Speed for the time on stopwatch
What 3 things can happen when a wave hits a boundary?
Absorbed: it transfers energy to the second material’s energy stores
Transmitted: It goes through material (often at different velocity’s which lead to refraction).
Reflected: it can bounce of the second material and sent back.
What is the one simple rule for reflection?
Angle at incidence = angle at reflection
What does the reflection of visible light let us do?
It lets us see colour as the light bounces of objects into out eyes.
What is clear reflection?
When light reflects of smooth surfaces (eg mirror) all in the same direction.
What is White light?
It is made of all the colours of light which have different wavelengths.
What happens to the colours of light when white light is reflected?
When white light is reflected, colours of light reflect as same angle and DON’T split as they follow reflection rule (angle at incidence = angle at reflection).
What is refraction?
When a wave bends
What happens to wave speed when wave crosses a boundary?
It changes speed
Eg from glass to air the wave speed will change.
What happens to frequency when wave crosses a boundary?
Frequency remains the same
What happens to wavelength when wave crosses a boundary?
It changes wavelength
When it slows down -> wavelength decreases
When it speeds up -> wavelength increases.
- This is due to equation wave speed = frequency x wavelength
if frequency is the same and speed decreases = the wavelength decreases
What is the normal?
It is the imaginary perpendicular line of the surface of the boundary.
What happens when a wave slows down?
It bends towards the normal, decreasing the wavelength
What happens when a wave speeds up?
It bends away from the normal, increasing the wavelength
Sound waves and different mediums?
Sound waves travel faster in denser materials.
Hence from air to water, it bends away form the normal, its wavelength increases (speeds up).
Electromagnetic waves and mediums?
EM waves (such as light) travel slower in denser materials.
Hence from air to water, it bends towards the normal (if refracted) , its wavelength decreases (slows down)
What can determine how much an EM wave is refracted?
Its wavelength
- shorter wavelengths refract more
- Longer wavelengths refract less
Colours of light and wavelengths.
Shortest wavelength to longest:
Violet Indigo Blue Green Yellow Orange Red
Colours of light and mediums:
They travel the same speed (3x10^8m/s) in air
In denser material, light ray bends towards normal, wavelength decreases, It slows down.
- ->Violet refracts most (slows down most)
- ->Red refracts least (slows down least)
What is specular reflection?
When wave are reflected in single direction on smooth surface.
An example of specular reflection?
When light is reflected by a mirror.
What is scattered reflection?
When waves are reflected by a rough surface causing waves to reflect is different directions.
Why does scattered reflection occur?
This is because all the normals are different for each incident ray, so angle at incidence is equal to angle of reflection.
An example of scattered reflection?
When it reflects off rough surface it results in surface looking matt (dull and not shiny) like rough paper.
Experiment to investigate reflection?
- Need a ray box, mirror, protractor and a dark room (keeping light constant throughout experiment)
1) Take paper and draw solid line horizontally across it then draw dotted line perpendicular to the solid line (normal)
2) Place a flat mirror so it lines up with solid line
3) Using ray box, shin beam of white light at mirror, so light hits mirror where the normal meets mirror.
4) Trace incident and reflected light rays
5) Measure angle of incidence and reflection using protractor
6) Repeat steps with different angles of incidence and you will see angle of reflection is always the same
7) This works as the mirror gives a clear reflection of the ray and none of the light is reflected.
Drawing a diagram for reflection?
1) Draw normal perpendicular to surface and light ray meets the normal at surface
2) Draw reflected line with same angle as angle of incidence.
3) Always put arrows on the rays
4) If there are multiple rays on smooth surface, the reflected rays will be parallel.
Drawing ray diagram for refraction?
1) Draw normal perpendicular to any surface
2) If light ray travels into denser material it slows down, bends toward normal
3) If it travels into a less dense material it speeds up, bends away from normal
Where is angle of incidence?
It is always between the incident ray and the normal
Where is the angle of reflection?
It is always between the reflected ray and the normal
What should a diagram for a light ray travelling from air to glass then emerging back out to air?
1) When incident ray enters glass (denser) it slows down and bends towards the normal
2) When leaving the glass to air it bends away from the normal as it speeds up (goes into a less dense material).
How does wavelength contribute to how much a wave refracts?
Shorter wavelengths refracts more
Larger wavelengths refract less
What happens when white light travels through a triangular prism?
- A rainbow is formed
- The colours of light bends towards the normal as they go into a denser material (glass) for air.
- Every colour of light has a different wavelength so they refract different amounts.
- > Violet (shortest wavelength), refracts most
- > Red (longest wavelength), refracts least
How to investigate the refraction for light?
- You need a ray box, coloured filters and a triangular prism
1) Place one coloured filter over ray box, then shine beak through prism (which is laying flat on a piece of paper) at an angle toward the normal.
2) Trace incident ray and emerging ray onto the paper and remove prism.
3) Draw refracted ray by joining the incident ray and emerging ray
4) Repeat using a different coloured filter keeping angle of incidence the same.
How does a sound wave travel from a speaker to a solid?
1) A speaker converts an electrical signal to a motions (by vibrating the diaphragm back and forth. This causes surrounding air particles to vibrate (a sound wave)
2) Sound wave passes through air as a series of compressions and rarefactions. Air particles don’t move but instead pass on vibrations
3) When sound wave hits a solid it causes the surface of the solid particles to vibrate. These particles hit more solid particles causing them to vibrate and it is passes on as a series of vibratiosn.
What happens to frequency when sound waves travel into different medium?
It doesn’t change
What happens to wavelength when sound waves changes speed?
-Frequency doesn’t change therefore wavelength has to change (wave speed = wavelength x frequency)
Speeds up = longer wavelength
Slows down = shorter wavelength
What happens when sound wave hits hard flat surface?
It reflects
What are echoes?
They are reflected sound waves.
What happens to sound waves in space?
sound waves can’t travel in space as it is mostly vacuum (there are no particles to vibrate)
How does a person hear sound?
1) Sound wave enters ear through pinna
2) Sound wave travels through the auditory canal
3) Sound waves hit eardrum and make it vibrate
4) The ossicles transmit vibrations from eardrum to cochlea
5) Cochlea converts vibrations to electrical signals
6) Auditory nerve sends the electric signals to brain
What frequency can young people hear from?
What happens to this figure as you get older. Why?
From 20Hz (Low pitch )to 20000Hz (High pitch)
Older you get the upper value decreases due to wear and tear of the cochlea or auditory nerve
What are partial reflections?
If a wave is transmitted , some waves are usually reflected off the boundary too
Quick definitions of what a ultrasound does?
It uses sound with frequencies higher than 20,000 Hz to see hidden thing.
- Can only see soft tissues
- If we know speed of wave and time it takes for reflections to reach detector to find how far the boundary is.
How do ultrasounds work?
1) There is an ultrasound emitter which also can detect ultrasounds
2) It emits ultrasounds which are partially reflected at the boundary (like tissues)
3) The reflected ultrasound is detected and the transmitted ultrasound hits another boundary and reflects
4) If we know speed of wave and time it takes for reflections to reach detector to find how far the boundary is and an image can be produced
Where in the body are examples ultrasounds can be used to from an image?
- Producing image of developing foetus
- soft tissues and tissues like kidneys, liver bladder
How can ultrasounds be used to find flaws (like cracks) in materials?
1) ultrasound wave entering material will usually be reflected by far side of material
2) If there is a flaw like a crack it will be reflected sooner by crack and can be detected.
What are sonars?
They are used by boats and submarines to find distance to seabed or locate objects in waters by using high frequency sound waves
- The time between a pulse of sound being transmitted by boat / submarine and detected and the speed of sound in water can be used to calculate the distance of the reflecting surface or object
EG) If wave transmitted by boat is detected 0.1s later and the speed of sound in water is 1,480 m/s. Find distance to seabed?
time for ultrasound to travel to seabed and back again = 0.1 s
time for ultrasound to travel to seabed = 0.1 s ÷ 2 = 0.05 s
distance to seabed = 1,480 × 0.05 = 74 m
The depth of water is 74 m.
What type of wave are electromagnetic waves?
Transverse waves
What speed do electromagnetic wave travel at in vacuum?
3x10^8m/s
What is the relationship between frequency and wavelength in electromagnetic waves?
Long wavelength -> low frequency
Short wavelength -> High frequency
What is the relationship between energy transferred and frequency in Electromagnetic waves?
Higher frequency -> Higher energy transferred
Low frequency -> Lower energy transferred
What are the seven EM waves?
Red - Radio waves
Meat - Microwaves
Is - Infrared waves
Very - Visible light
Unsanitary - Ultraviolet waves
Except - X-rays
Giraffes - Gamma rays
EM waves and their frequencies and wavelengths:
HIGHEST FREQUENCY + SHORTEST WAVELENGTH Gamma ray X-ray Ultraviolet Visible light Infrared Microwave Radiowave LOWEST FREQUENCY + LARGEST WAVELENGTH
What is the only EM wave the eye can see?
Visible light
Different implications on human health depending on how the EM wave is transmitted reflected or absorbed?
Radiowave: transmitted through body without being absorbed
Microwaves: Some wavelengths of microwaves can be absorbed, causing heating of cells
Infrared and visible light: mostly reflected or absorbed by skin, can cause some heating. Infrared can causing burning if skin too hot
Ultraviolet: also absorbed by skin, but due to higher frequency it transfers more energy, causing damaging. When enters living cells, collides with atoms which cause ionisation (knock off electrons), This damages cells leading to genetic mutation and cancer, lead to tissue damage or radiation damage.
X-rays and Gamma ray: also cause ionisation (can lead to tissue damage and cancer. but have higher frequency so transfer more energy, cause more damage. Can pass through skin, can be absorbed by deeper tissue
Uses of radio waves?
- Used for communication
1) Em waves are just oscillating electric and magnetic fields
2) Alternating currents in electrical circuit causes charges to oscillate creating oscillating electric and magnetic field - an EM Wave
3) This EM wave has the same frequency as the current that created it - can create a radio wave
4) Em waves also cause charged particles to oscillate, this induces alternating current of same frequency of EM wave that induces it.
5) If you have transmitter and receiver, you encode information (eg a TV show) in an a.c and then transmit it as a radio wave. This wave induces an a.c current receiver
Uses of microwaves?
Communication and cooking
1) Communication to and from satellites (includes Satellite TV and mobile phones) with microwave with a wavelength that passes easily through Earth’s watery atmosphere.
2) Cooking food we use microwaves. Waves penetrate food into food before being absorbed and transfer energy to water molecules, warming it up. The water molecules transfer the energy to the rest of the molecules in the food - cooks food quickly
Uses of infrared waves?
- Used to increase or monitor temperature and cooking
1) Absorbing infrared waves it heats things up, used in cooking to heat up food as it absorbs IR waves
2) In medical imaging, IR cameras detect the increased temperatures caused by infections emitting IR radiation
3) IR Cameras can detect IR radiation and monitor temperature, they turn IR radiation into electrical signal, display it on screen. The hotter an object, brighter it appears
Uses of visible light?
- Can travel through optical fibres
1) Used for communication using optical fibres (carry information long distance as pulses of light)
2) Optic fibres work by bouncing light of sides of very narrow core. The pulse of light enters the core at certain angle and is reflected again and again until it emerges outside other end.
3) Optical fibres used for telephones and internet cable
What are Ultraviolet waves used for?
- Florescent lights
1) Ultraviolet waves are absorbed making electron move up energy levels (becomes excited) and they move down energy shells gradually releasing visible light. They are energy efficient - use when light is needed for long period of time (like in classroom)
2) Security pens
What are X-rays used for?
- To see through things
1) They are transmitted by flesh and absorbed by denser materials like bones or metal
2) The brighter bits on image are where fewer X rays get through, producing negative image
How are Gamma rays used for?
- Sterilisation and cancer treatments
1) Sterilisation: they kill microbes (in food or medical industry)
2) Cancer treatments: Radiation targeted at cancer cells to kill them
How are infrared waves used in medical imaging?
- Tell you where injuries and infections are
1) Infected area are hotter the other areas, gives off more IR waves. This is detected by IR cameras
How are X-rays used in medical imaging?
- produces image of bones
1) X-rays transmitted through soft tissues but absorbed by denser materials like bones and metal
2) If lots of X-rays are used it can produce high resolution images of both soft and hard tissues in body (this is because not all X rays are transmitted by soft tissues and some are absorbed. CT scans
How are Gamma Rays used in medical imaging?
- See how things move throughout the body
1) Gamma rays are transmitted by skin, soft tissues and bones, so it can be detected outside body by Gamma camera
2) Radiotracers are injected or swallowed and as they move through body they emit gamma rays
3) These rays can be detected by Gamma camera outside body
Compromises in medical imaging:
-Infrared waves:
ADV: completely safe
DIS: only tell us about temperature
- Ultrasound waves:
ADV: completely safe and can give live image
DIS: give fuzzy and can only be used to make image of soft tissue - X-rays:
ADV: Clear image of bones
DIS: Are ionising, can cause damage to cells
Can only see bones
-Gamma rays:
ADV: can tell us information on how body is working
DIS: Very ionising
How do we see the colour of opaque objects?
Opaque objects don’t transmit light and only absorb and reflect some visible light waves.
The colour of the opaque object depends on which wavelengths of light are reflected (eg a red apple appears red as they red part of visible light spectrum is reflected)
How does mixing together colours work in terms of wavelengths of light.
Only colours that cannot be made by mixing is primary colours : red, blue, green
An object can appear a certain colour as more than one wavelength of light is reflected (eg a banana may look yellow as yellow light is reflected or both red and green light is reflected)
How do white objects appear white?
They reflect all colours of light equally
How do black objects appear black?
They absorb all colours of light equally
How do we see transparent (see-through) and translucent (partially see-through) objects?
They transmit light
Not all light is absorbed or reflected - some (or most for transparent objects) are transmitted
How do colour filters work?
They filter out different wavelengths of light so certain colours are transmitted and the rest are absorbed
How does a primary colour filter work?
It only transmits that colour (eg if we shone white light at a blue colour filter it only transmits blue light. The rest are absorbed)
How to we see a blue object through a blue colour filter?
The blue light reflected from objects surface, transmits through filter for us to see.
What happens if we look at a different coloured object from a different colour filter (eg looking at a red object from a blue filter)?
Object will appear black as all the light reflected from the object will be absorbed by the filter.
How do non primary colour filters work?
They transmit both the wavelength of light corresponding to that colour and the wavelengths of the primary colour that can be added together to make that colour. (Eg cyan can be made by green and blue so a cyan colour filter will transmit cyan, blue and green light through)
What do concave lens do to light?
They cave inwards and diverge light (spread out)
What is an axis on lens?
The line passing through the middle
What is the principle point (focal point) on a concave lens?
Point where rays hitting the lens parallel to axis appear to come from. Trace them backwards until they all appear to meet up at point behind the lens
What is a convex lens?
It bulges outwards causing light rays to converge (move together)
What is the principal focus (focal point) on a convex lens?
The principal focus of a convex lens is where rays hitting the lens parallel to axis meet.
What is the focal length?
The distance from the centre of lens to prinicle focus. There is a principal focus on each side of any lens
How do we describe images from ray diagrams?
1) Upright or inverted
2) Real or virtual: If it is on opposite side of lens it is real. If it is on the same side as the object it is virtual
3) Magnified or diminished
How do you draw a concave ray diagram?
1) Draw ray from top of object to the lens
2) Draw another ray from top of object to middle of lens
3) The first ray is refracted (concave diverge light)
4) continue refracted line as a dotted line to a principal focus
5) Mark where the rays meet at that is the top of new image
How do we know if a ray diagram is concave or convex?
CONCAVE: The arrow on lens (middle line) points inward
CONVEX: The arrow on lens points outwards (like a normal arrow)
How do you draw a convex ray diagram?
1) Draw a ray from the top of an object to the lens
2) draw another lens from the top of the image to the middle of the lens and continue it.
3) As convex lens converge light, the ray parallel to the axis is refracted through principal focus.
4) Mark where the rays meet. That is the top of the new image
How can concave lens correct vision?
- Help with short sighted (cant see far)
1) Light meets too early, before the retina (eyeball too long or light refracted too much)
2) Concave lens converges light to focus it on retina
How can convex lens correct vision?
- Helps with long sighted (Can’t see close)
1) Light meets too late (eyeball too short or light not refracted enough)
2) Convex lens converge light to focus it on retina
What effect does changing frequency and amplitude of sound waves affect the noise?
Changing frequency: changes pitch of sound
- Increased frequency = higher pitch
- Decreased frequency = lower pitch
Changing amplitude: changing volume of sound
- Increased amplitude = louder
- Decreased amplitude = Quieter
Difference between light and sound waves?
Light waves: - Transverse wave - Non-mechanical wave -> doesn't need particles to travel - Faster in less dense mediums (less particles): Vaccum: fast (3 x 10^8m/s) Air: fast (3 x 10^8m/s) Water: denser, slower Glass: very dense, travels slower
Sound waves:
-Longitudinal wave
- Mechanical wave -> requires particles to travel
- Faster in denser mediums (more particles):
Vaccum: empty space, sound can’t travel
Air: low density, less particles, travels slow
Water: more dense, more particles, travels faster
Iron: most dense, moves very fast
Difference between microwaves and Infrared waves?
-Both used for cooking
Microwaves: Are absorbed by H2O molecules in food. making them vibrate. They transfer energy to the rest of the food molecules.
Infrared (used in ovens): only heat the surface of food
Difference between radio waves and microwaves?
-Both used for communication
Radio waves: these are emitted into the earth’s atmosphere but cannot leave it. They are reflected and reach desired place
Microwaves: When microwaves emitted they can leave Earth’s atmosphere as they are a higher frequency. Satellites outside the Earth’s atmosphere reflect waves back to Earth and desired place.
