P6 - Waves

Question 1

What do aves transfer

Answer 1

Transfer energy in the direction they’re travelling

Question 2

What happens when a wave travels through a medium

Answer 2

The particles of the medium oscillate and transfer energy between each other. Particles stay in the same place, only energy is transferred

Question 3

What’s the amplitude of a wave

Answer 3

Maximum displacement of a point on the wave from its undisturbed position.

Question 4

What’s the wavelength of a wave

Answer 4

Distance between two adjacent waves

Question 5

Frequency of waves

Answer 5

Number of complete waves passing a certain point per second
1hertz is 1 wave per second

Period = 1/frequency

Question 6

What vibrations do transverse waves have

Answer 6

Sideways vibrations

Question 7

Key information of transverse waves

Answer 7

Oscillations are perpendicular to the direction of energy transfer 
Most waves are transverse 
All EM waves 
Ripples and waves in water 
Wave in a string

Question 8

What vibrations do longitudinal waves have

Answer 8

Parallel vibrations

Question 9

Key information of longitudinal waves

Answer 9

Oscillations are parallel to the direction of energy transfer
E.g sound waves in air

Question 10

1. What do you use to measure the speed of sound
2. What do you use to measure speed of water ripples
3. What do you use to measure waves on a string

Answer 10

1. Oscilloscope
2. Ripple tank
3. Wave equation

Question 11

What happens if when a wave meets a boundary between two materials and why?

Answer 11

Either three things
Wave is absorbed by second material
Wave is transmitted through second material
Wave is reflected

What happens depends on wavelength, material properties

Question 12

What happens when the wave is absorbed by the second material

Answer 12

Wave transfers energy to materials energy stores (normally thermal )

Question 13

What happens when a wave is transmitted through the second material

Answer 13

Wave carries on traveling through new material and often leads to refraction. This is used in communication as well as glasses and cameras

Question 14

What happens if the wave is reflected

Answer 14

Incoming ray is sent back (how echos are made)

Question 15

Example of transferring energy to an absorbed

Answer 15

Camp fire transfers infrared radiation to surroundings. This infrared is absorbed by objects and transfers energy to objects thermal, energy stores

Question 16

All EM waves travel the same speed through

Answer 16

The air or a vacuum

Question 17

What are electromagnetic waves

Answer 17

Vibrations of electric and magnetic fields

Question 18

What speeds to the em waves vary through

Answer 18

10^-15 to 10^4

Question 19

List the EM waves in order and their wavelengths and properties

Answer 19

Radio waves(10^4) microwaves(10^-2) infrared radiation(10^-5) visible light(10^-7) ultra violet(10^-8) x-rays(10^-10) gamma rays(10^-15)
Radio waves are the longest wavelength but the lowest frequency (carries on as a sequence going down the waves)

Question 20

What happens when a wave crosses a boundary between 2 materials

Answer 20

It changes speeds

Question 21

What happen if wave is travelling along the normal when it crosses a boundary

Answer 21

Changes speed but isn’t refracted

Question 22

What happens if the wave hits the boundary at an angle

Answer 22

It’d refracted. Bends towards normal if it slows down, bends away from normal if it speeds up. How much it’s refracted depends on wave speed and materials density
Higher density = slower light waves travel (bend towards normal)
Wavelength changes when refracted

Question 23

What is optical density of a material

Answer 23

A measure of how quickly light can travel through it

Question 24

What are rays

Answer 24

Rays are straight lines that are perpendicular to wave fronts (show wave direction)

1. Draw boundary and normal
2. Draw incident ray (first ray)
3. Draw refracted ray (second ray)

Question 25

What is a wave front

Answer 25

Line showing all points on a way that are in the same position as each other after a given number of wavelengths
When wave crosses boundary at an angle, only part of the front crosses boundary first
If new material is dense = travels slower

Question 26

What are EM waves made up of

Answer 26

Oscillating electric and magnetic fields

Question 27

What are alternating currents made up of

Answer 27

Oscillating charges. As the charges oscillate they make EM waves
Frequency of wave produced will be equal to the frequency of the Alternate current

Question 28

How are radio waves produced

Answer 28

Use an alternate current in an electrical circuit.
Object in which charges oscillate in to create radio waves in an transmitter
Energy carried by waves transferred to electrons in the material of receiver
Energy causes electrons to oscillate ans generate alternate current
Current has same frequency of radio waves produced

Question 29

What are radio waves used for

Answer 29

Used for communication.
Long radio waves transmitted from London to halfway round the world. Wavelengths refract and bend around the surface of earth
Short wave radio signals received at long distances as they’re reflected off ionosphere
Blue tooth uses short RW to send data
RW for tv and radio are short

Question 30

What are micro waves used for

Answer 30

Communicate to and from satellites
Need to use micro waves as they pass easily through the watery atmosphere
Satellite Tv get signal from transmitter transmitted into space. Picked up by satellite receiver dish which transmits a signs in a different direction back to earth which is received by satellite dish on ground.
There’s a time delay due to distance

Question 31

How are micro waves used in microwave ovens

Answer 31

Micro waves to be absorbed by water molecules in food (different wave length)
MW penetrate few cm Into food before being absorbed and transfer energy to water molecules in food to heat up
Watermolecules transfer energy to rest of molecules to heat up

Question 32

What is infrared radiation used for

Answer 32

Infrared radiation is given out by all objects
Infrared cameras are used to detect infrared radiation and monitor temperatures. They detect IR and turn it into an electric signal which is displayed on a screen hotter = brighter
Absorbing IR causes objects to heat
Used in electric heaters as they contain a long wire that emits IR which is absorbed by objects and air in the room and transfers energy to thermal energy stores

Question 33

Visible light uses

Answer 33

Lights
Optic fibres are thin glass or plastic fibres that carry data over long distances as pulses of visible light which work because of reflection
Light rays bounced back and forth until they reach end of fibre
VS used in optic fibres as light is easily refracted enough and not easily absorbed or scattered.

Question 34

Uses of ultra violet

Answer 34

Suntans (UV lamps)
UV produced by sun
Fluorescent lights generate UV which is absorbed and emitted as visible light

Question 35

Uses of x rays and gamma rays

Answer 35

X rays easily pass through flesh but not denser materials like bones
Radio graphics use both to treat cancer - carefully directed to kill cancer cells

Question 36

Dangers of EM waves

Answer 36

High frequency waves like UV and X-rays and gamma transfer lots of energy and can deal lots of damage
UV damages surface cells - sunburn , skin to age prematurely + skin cancer risk
X rays and gamma rays types of ionising radiation - gene mutation or cell destruction and cancer