AQA P1.5 Waves
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- Created by: Rchilds
- Created on: 16-05-17 09:36
What is a wave?
Anything that transfers energy and information with no overall transfer of matter (particles)
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What is a longitudinal wave?
A wave where the oscillations (vibrations) are parallel (in the same direction) as the energy transfer
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What is a transverse wave?
A wave where the oscillations (vibrations) are perpendicular (at 90 degrees to) as the energy transfer
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Give examples of longitudinal waves
SOUND (pretty much the only example you need to know), also pressure waves in slinkys and p-waves from earthquakes
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In a longitudinal wave, what are the areas of the 'squashed up wave' called?
Compressions
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In a longitudinal wave, what are the areas of the 'stretched out wave' called?
Rarefactions
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Give examples of transverse waves
All electromagnetic waves (radio wave, microwaves, infrared radiation, visible light, ultra violet, x-rays, gamma rays), water waves, slinkey waves and string waves when you shake them from side to side. S-waves from earthquakes
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What is the frequency of a wave?
How many waves pass a point every SECOND. e.g. if asked what does 300Hz mean you can say '300 waves pass a point every second'
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What is frequency measured in?
Hertz (Hz)
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What is the amplitude of a wave?
The height of a wave measured from the MIDDLE to the very top (this is the same as the middle to the very bottom)
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What is the wavelength of a wave?
The distance between a point on a wave to the exact same point on the next wave (usually peak to peak)
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What is the electromagnetic spectrum in order of increasing frequency/decreasing wavelength?
Radiowaves, microwaves, infrared radiation, visible light, ultraviolet, x-rays, gamma rays
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Which electromagnetic wave has the highest frequency?
Gamma
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Which electromagnetic wave has the highest energy?
Gamma (because it has the highest frequency)
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Which electromagnetic wave has the lowest frequency?
Radio waves
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Which electromagnetic wave has the longest wavelength?
Radio waves
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Which electromagnetic wave has the shortest wavelength?
Gamma
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What do all electromagnetic waves have in common? (note: they might phrase this given specfic examples e.g. what do UV and visible light have in common)
(1) They are all transverse (2) they all travel at the same speed through a vacuum (3) they can all travel through a vacuum (4) they all can be reflected, refracted and diffracted (5) they can all transfer energy and information
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What are the differences between the electromagnetic waves?
They have different frequencies, wavelengths, energies, uses and dangers
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The electromagnetic spectrum is a continuous spectrum. Roughly what is the range of the wavelengths of the EM spectrum?
10^4 to 10^-15 meters
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What is reflection?
When a wave hits a new material and 'bounces off' it
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What is the law of reflection?
The angle of incidence = the angle of reflection
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What is the normal line?
An imaginary line drawn at the point where light hits a surface, it must be 90 degrees to the surface
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When looking at light behaviour, where do we measure all angles from? e.g. the angle of incidence, angle of reflection, angle of refraction...
The angle is always between the normal line and the light ray
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Describe the image formed in a mirror
virtual, upright, the same size as the object, laterally inverted (left is right and right is left)
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Where does the image in a mirror appear?
The distance between the image and the mirror is the same as the distance between the object and the mirror
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How do you draw a reflection diagram? (cheat method)
(1) draw the image onto your page so it is the same distance from the mirror as the object is, label this 'I'. (2) Draw a straight line between the image and the object, put an arrow point away from the object. (3) Draw a straight line, (continued)
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reflection continued
... at and angle, going away from the image and crossing over the mirror, add an arrow point away from the image. (4) Draw a line connecting the object to the second line where it crosses the mirror, add an arrow. (5) draw a dotted normal line on
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How do you draw a reflection diagram? (scientific method)
1. Draw two rays leaving the object and hitting the mirror, at any angles. 2. Where they hit the mirror, draw on dotted normal lines at 90 degrees to the surface (one for each ray). 3. Reflect these lines using the law of reflection. (continued)
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reflection 2 continued
4. these reflected rays will never cross so trace them backwards to the other side of the mirror so you can find out where they would cross 'in theory'. 5. where they would cross in theory is where the image is formed
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Where are images formed?
Where light rays cross over
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What is a virtual image?
Light seems to be coming from the image but the light rays don't actually cross there (light looks like it's coming from somewhere it isn't e.g. in reflection and refraction). It cannot be projected onto a screen
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What is a real image?
An image formed where light rays do actually cross over, so it can be projected onto a screen.
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What is refraction?
When a wave enters a new material it will change speed, this can cause it to change direction
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What happens when light enters a denser material?
It bends towards the normal line
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What happens when light enters a less dense material?
It bends away from the normal line
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What happens when light enters a new material at 90 degrees to it (i.e. along the normal line)?
It DOES NOT change direction
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What is diffraction?
When a wave goes through a gap or around an object, it spreads out
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When does maximum diffraction happen through a gap or around an object?
The wave will spread out the most through a gap, when the gap size is similar to the wavelength of the wave
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When does maximum diffraction happen around an object with only one open edge e.g. something attached to the floor?
The wave will spread out the most around an object, when the wavelength is as big as possible
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Why can houses in the shadow of mountains (or similar) receive radio signals but not TV signals?
Radio signals use radiowaves, TV signals use microwaves.When the waves pass around the mountain they are diffracted, but RW are diffracted more as they have the longer wavelength. RW spread out to reach the house but the MW don't spread enough
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What are uses and dangers of radiowaves?
Uses: Communication (radio and TV), Dangers: no known dangers
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What are uses and dangers of microwaves?
Use: Communication (internet, mobile phones, satellite TV), Dangers: microwaves make water vibrate and heat up so it can cause the internal heating of body cells
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What are uses and dangers of infrared radiation?
Uses: Communication (remote controls, optical fibres, data transmission) Dangers: infrared is heat radiation so can cause skin burns
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What are uses and dangers of visible light?
Uses: communication (Morse code etc) and photography, Dangers: damage to retina in eyes if very bright
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Why are UV, X rays and gamma rays dangerous?
They have enough energy to be ionising. If they ionise cells they can kill them, if they ionise DNA in cells they can mutate them and cause cancer
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What does ionise mean?
Remove (or add) electrons to atoms, making them into charged ions
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What are the uses and x-rays and gamma rays?
Medical imaging
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What are the uses of ultraviolet light?
tanning (sun beds), detecting bank note forgery, killing bacteria in water
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Other cards in this set
Card 2
Front
What is a longitudinal wave?
Back
A wave where the oscillations (vibrations) are parallel (in the same direction) as the energy transfer
Card 3
Front
What is a transverse wave?
Back
Card 4
Front
Give examples of longitudinal waves
Back
Card 5
Front
In a longitudinal wave, what are the areas of the 'squashed up wave' called?
Back
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