3-waves Flashcards
what is the unit.symbol for wavelength?
λ
what is a wavelength?
the diatance from one peak to the next
what is the symbol/definition for frequency?
how many (complete) waves there are per second (passing a certain point)
f
what is amplitude?
the height of a wave (rest (middle) to trough or rest to crest)
what is the speed of a wavelength?
the velocity of a wave aka the distance a wave travels in a given amount of time
what is the unit/symbol for speed?
m/s, v
unit for frequency?
Hz
what is period?
the time taken for one complete wave to pass a point.
what is the symbol for a period?
T
what is the equation linking frequency and period?
f = 1/t (1 being the number of waves)
what is the equation for wave speed?
wave speed = frequency x wavelength
or v = f x λ
what is the unit for wavelength?
m, metres
what is frequency?
How many waves pass a point in a second
What is a transverse wave (and an example)?
In a transverse wave the oscillations are perpendicular to the direction of energy transfer. The ripples on a water surface are an example of a transverse wave.
Sound waves are transverse
What is a longitudinal wave (and an example)?
In a longitudinal wave the oscillations are parallel to the direction of energy transfer.
E.g., sound waves, ultrasound waves
Explain the difference between Transverse vs Longitudinal waves
Both the transverse and longitudinal waves have different directions of oscillations. Transverse waves will have oscillations perpendicular to the direction of travel. Longitudinal waves will have oscillations parallel to the direction of travel, as shown in the diagram.
What is a wavefront?
when two or more waves move together, they have wavefronts.
wavefronts are imaginary planes that cut across all the waves, connecting the points on adjacent waves which are vibrating together.
the distance between each wavefront is equal to one wavelength i.e. each wavelength is at the same point in the cycle
( An imaginary surface representing points of a wave that are at the same point in their cycle.)
What do waves transfer?
Energy and information without transferring matter
Can all waves be refracted and reflected or not, including light waves?
Yes, they can
What is the law of reflection?
The normal is a line at right angles to the barrier. The angle of incidence i, is the angle between the direction of travel (the green line) for the incident waves and the normal.
The angle of reflection, I, is the angle between the direction of travel (the green line) for the reflected waves and the normal.
The angle of incidence always equals the angle of reflection.
What is the relationship between refractive index, angle of incidence, and angle of refraction?
N = refractive index
n = sin i / sin r
What is refraction?
Process by which a wave changes speed and sometimes direction upon entering a denser or less dense medium, eg a light ray changes direction when refracted by a lens. is the change in direction of a wave at such a boundary.
What is the relationship between the critical angle and the refractive index?
sin c = 1 / n
Can longitudinal waves be reflected and refracted?
yes
Define amplitude, frequency, wavelength, period of a wave
Amplitude – distance form a peak to the middle or from a trough to the middle
Wavelength- the distance between two peaks or two troughs (or two equivalent points)
Time period- time taken for one wave to be produced
frequency- wave produced per
second
are most waves longitudinal or transeverse?
transverse
name some examples of transverse waves
light and all other EM waves
a slinky wiggles up and down
waves on strings
ripples on water
(vibrations go side to side compared to direction as wave traveling)
name some examples of longitudinal waves
sound and ultrasounds
shock waves e.g., some seismic waves
a slinky when you push the end
(vibrations in the same direction as wave traveling)
what is the doppler effect?
the waves produced by a source which is moving towards or away from an observer will have a different wavelength than they would if the source were stationary. this is because the wave speed it constant, so it the source is moving, it ‘catches up to the waves in front of it’. this causes the wavefronta to bunch up in front of the moving source and spread out behind it. therefore, the frequency of a wave from a source moving towards you will be higher snd its wavelength will be shorter than the wave produced by the source. the frequency of the source moving away will be lower and its wavelength will be longer thant the wave produced by the source
look at diagram on pg 28 in cgp for help
what are the 7 types of EM waves?
radio waves, microwaves, infra-red waves, visible lgiht, ultra violet, x rays, gamma rays
what is the wavelength of a radio wave?
1m - 10^4 m
what is the wavelength of a micro wave?
10^-2 m (1cm)
what is the wavelength of an infra-red wave?
10^-5m (0.01mm)
what is the wavelength of an X-ray wave?
10^-10m
what is the wavelength of
an ultraviolet wave?
10^-8m
what is the wavelength visible light?
10^-7m
what is the wavelength of
a gamma ray?
10^-12m
what are all EM waves?
transverse and travel at the same speed through free space (aka in a vacuum)
which em wave has the longest wavelength?
radio wave
which em wave has the shortest wavelength?
gamma ray
which em wave has the highest frequency ?
gamma
which em wave has the lowest frequency ?
radio wave
what colour has longest/shortest wavelength?
longest - red (lowest frequency)
shortest - violet (highest frequency)
what is a main use of radio waves?
communications, (TV and FM radio broadcasting). (v short wavelength (10cm-1m)) - to get reception for this you must be in direct sight of the transmitter (signal doesnt bend around hills)
what can longer and shorter radio waves be used for?
longer - (1-10km) can be transmitted a long way because long wavelengths are bent around the curved surface of the earth
shorter - (10m-100m) can also be recieved at long distances from the transmitter because they are reflected from the ionosphere (layer of earth’s atmosphere)
what are microwaves used for?
satellite communications (for phones and transmissions) and heating food
what is infrared radiation used for?
tv remotes (the red light), thermal imaging (e.g., night vision goggles), heating (can be used in electrical grills) and to monitor temperature, (optical fibres for wifi transmitting data)
what are the dangers of radio waves?
there are no dangers
what are the dangers of microwaves?
cause internal heating of cells and body tissue
what are the dangers of infrared?
skin burn
what speed do all EM waves travel at in a vacuum?
3 x 10 ^8 m/s
What is special about EM waves
they don’t require a medium, e.g., can be in a vacuum, and they all travel at the same speed in a wavelength
what are the uses of visible light?
vision, photography, optical fibers, illumination, or decorative light
what are the dangers of visible light?
there are none
what are the uses of UV light?
detecting fake bank notes (using a pen), security markings, fluorescent lamps, sterilising water (kills bacteria)
what are the dangers of UV?
skin cancer, damage to surface cells, blindness
what are the uses of x-ray?
viewing internal structure of objects and materials including for medical applications e.g., detects fractured bones, security scanners in airports
what are the dangers of x ray?
cancer, mutation (of cells) because they are high energy causing the cell to split and mutate
what are the uses of gamma?
sterilising surgical equipment, killing bacteria in food (doesn’t leave a trace because it is just passing through it), detecting and killing cancerous cells e.g., radiotherapy however it is difficult to aim the cells in particular place in order to make sure it doesn’t spread
what are the dangers of gamma?
mutations of cells and cancer
what do medics wear to measure radiation?
dosimeters (which measure radiation)
what detects alpha, beta, and gamma rays?
a g-m (geiger-muller) tube
where can light signals travel?
through optic fibres
what can visible light also be used for?
communication using optical fibres because it can carry data over long distances as pulses of light
how do optical fibres work?
by bouncing waves off the sides of a very narrow core. the pulse of light enters the fibre at a certain angle at one end and it is reflected again and again until it emerges at the other end
where are optical fibres used?
used for telephone and broadband internet cables. they can also be used for medical purposes to see inside the body without having to operate
what type of waves are light waves?
transverse. they can be reflected and refracted
what happens when light reflects from an uneven surface?
you get diffuse reflection so the light reflects off at all different angles
what happens when light reflects from an even surface?
it is all reflected at the same angle and you get a clear reflection
what is the relationship between angle of incidence and angle of reflection?
angle of incidence = angle of reflection
what is the symbol for angle of incidence and angle of reflection
angle of incidence - i
angle of reflection - r
what is the incident ray?
the initial ray
what is the normal?
an imaginary line that is perpendicular to (at right angles) the surface of the point of incidence (where the wave hits the boundary)
it is usually represented as a dotted line
what is the angle of incidence and reflection?
angle from the incoming wave and the normal
reflection - angle between the reflected wave and the normal
how are virtual images formed?
light rays bounce off an object onto a mirror diverge, so the light from the object appears to be coming from a different place
what happens when a wave crosses a boundary between two substances?
it changes speed because waves travel at different speeds in different densities
how can a wave be refracted?
if a wave meets a different medium at an angle, one part of the wave hits the denser layer first and so on whilst another part carries on at the first, faster speed. so the wave changes direction nd it has been refracted.
how do you draw a ray diagram for a refracted ray?
1) First, start by drawing the boundary between your two materials and the normal (a line that is at 90° to the boundary).
incident light ray
1. Draw an incident ray that meets the normal at the boundary.
2. The angle between the ray and the normal is the angle of incidence.
(If you’re given this angle, make sure to draw it carefully using a protractor.)
3. Now draw the refracted ray on the other side of the boundary. If the second material is denser than the first, the refracted ray bends towards the normal (like on the right). The angle between the refracted ray and the normal (the angle of refraction) is smaller than the angle of incidence.
4. If the second material is less dense, the angle of refraction is larger than the angle of incidence.
describe a practical showing that rays passing through a glass block are refracted twice
- You can experiment with refraction using a light source and a rectangular block of a particular material (e.g. glass) resting on top of a piece of paper…
- Shine a light ray at an angle into the block, as shown. Some of the light is reflected, but a lot of it passes through the glass and gets refracted as it does so.
- Trace the incident and emergent rays onto the piece of paper and remove the block. You can draw in the refracted ray through the block by joining the ends of the other two rays with a straight line.
4) You should see that as the light passes from the air into the block (a denser medium), it bends towards the normal. This is because it slows down.
5) When the light reaches the boundary on the other side of the block, it’s passing into a less dense medium. So it speeds up and bends away from the normal.
(Some of the light is also reflected at this boundary.)
6) The light ray that emerges on the other side of the block is now travelling in the same direction it was to begin with — it’s been refracted towards the normal and then back again by the same amount.
describe a practical to see that triangular prisms disperse white light
If you shine white light into a triangular prism, different wavelengths of light refract by different amounts, so white light (which is a mixture of all visible frequencies) disperses into different colours as it enters a prism and the different wavelengths are refracted by different amounts. A similar effect happens as the light leaves the prism, which means you get a nice rainbow effect.
describe a practical to investigate the refractive index of glass.
1) Draw around a rectangular glass block on a piece of paper and direct a ray of light through it at an angle. Trace the incident and emergent rays, remove the block, then draw in the refracted ray between them.
You then need to draw in the normal at 90° to the edge of the block,
Normal
at the point where the ray enters the block.
3) Use a protractor to measure the angle of incidence (i and the
Measure these two angles
The refractive index of glass should be around 1.5, so if you get a ridiculous answer then you’ve gone wrong somewhere.
angle of refraction (r), as shown. Remember — these are the angles made with the normal.
4) Calculate the refractive index (n) using Snell’s law: n =
sin i sin r
5) you should have found the refractive index of the block.
what is the equation for the refractive index?
refractive index, n = speed of light in a vacuum, c / speed of light in a material, v
n = c/v
what does the refractive index tell us?
tells you how fast light travels in that material
describe a practical to investigate the refraction of light using semi-circular blocks.
light going from a material with a higher refractive index to a material with a lower refractive index speeds up and so bends away from the normal — e.g. when travelling from glass into air.
1. If you keep increasing the angle of incidence (i), the angle of refraction (r) gets closer and closer to 90.
2. Eventually i reaches a critical angle C for which r = 90°. The light is refracted right along the boundary.
3. Above this critical angle, you get total internal reflection - no light leaves the medium.
4. An experiment to demonstrate this uses a semicircular block instead of a rectangular one. The incident light ray is aimed at the curved edge of the block so that it always enters at right angles to the edge.
This means it doesn’t bend as it enters the block, only when it leaves from the straight edge.
5. To investigate the critical angle. C, mark the positions of the rays and the block on paper and use a protractor to measure i and r for different angles of incidence. Record your results in a table.
what does it mean if the angle of incidence is less than the critical angle?
most of the light passes out but a little bit is internally reflected
what does it mean if the angle of incidence is more than the critical angle?
no light comes out. it is all internally reflected i.e. total internal reflection
what does it mean if the angle of incidence is equal to the critical angle?
the emerging ray comes out along the surface. there is a lot of internal reflection.
what are optical fibres made out of?
plastic or glass
what do optical fibres consist of
a central core surrounded by cladding with a lower refractive index. the central core is so narrow that light signals passing thorugh it always hit the core-cladding boundary at angles higher than C so the light is always totally internally reflected
what is the critical angle?
the critical angle is the angle of incidence at which light changes from refracting to total internal reflection.
it is also when the angle of refraction is exactly 90°, then the angle of incidence.
what is total internal reflection?
when a light ray is completely reflected back into a denser medium when it reaches the boundary between two transparent materials
when does total intenral reflection occur?
Total internal reflection (TIR) occurs at the boundary between two media when:
All the incident ray in medium 1 is reflected back into medium 1
it occurs when the angle of incidence is greater than the critical angle and the incident material is denser than the second material
what happens when light passes into a less dense medium
When light passes between the boundary of an optically dense to a less dense medium and the angles of incidence are small
The refracted ray is strong
The reflected ray is weak
The weak ray is reflected back into the denser medium
This means some internal reflection occurs
when does refraction happen?
Refraction happens when the angle of incidence is smaller and total internal reflection happens when the angle of incidence equals the angle of reflection
what are some differences between total internal reflection and normal reflection
Normal reflection produces a less intense light compared to TIR
In TIR the light ray is brighter and more intense
Normal reflection occurs independent of the refractive indices of both media
For TIR to occur, the incident material must be denser than the second material
why are prisms useful for total internal reflection?
it allows us to see things that aren’t in our direct line of sight. e.g., this is how a periscope works
how is total internal reflection done in a prism?
the ray of light travels into one prism where it is totally internally reflected by 90 degrees.
it then travels to anotehr prism lower doen and is totally internally reflected by another 90 degrees.
the ray id now travelling parallel to its intial path but at a different height
explain the critical angle
When the angle of refraction is exactly 90°, then the angle of incidence is called the critical angle C. When the angle of incidence is greater than the critical angle none of it is refracted, the ray is totally internally reflected, and the law of reflection is obeyed, i = r.
The transformer supplies an output voltage of 2000 V a.c. to the wire grid.
The input voltage to the transformer is 230 V a.c.
(i) Give the name of this type of transformer.
step up
what is ionising?
ionization is the process of adding or removing electrons from an atom to create an ion:
why is a thermometer that is black good for detecting infra-red radiation?
darker, matt surfaces are better absorbers and emitters of infrared radiation
