P6

Question 1

amplitude

Answer 1

Of a wave is the maximum displacement of a point on the wave from its undisturbed position.

Question 2

wavelength

Answer 2

The distance between the same point on 2 adjacent waves.

Question 3

frequency

Answer 3

The no. of complete waves passing a certain point per second.
Measured in hertz. 1Hz is 1 wave per second.
From frequency you can find period of a wave using amount of time it takes for a full cycle of the wave.

Question 4

Transverse Waves

Answer 4

The oscillations (vibrations) are perpendicular (at 90 degrees) to the direction of energy transfer.
eg: all electromagnetic waves, ripples and waves in water, a wave on a string.

Question 5

Longitudinal Waves

Answer 5

The oscillations are parallel to the direction of energy transfer.
eg: sound waves in air.

Question 6

wave speed

Answer 6

The speed at which energy is being transferred (or speed the wave is moving at).
wave speed (m/s)= frequency (Hz) x wavelength (m)

Question 7

Oscilloscope practical 1

Answer 7

1. set up oscilloscope so detected waves at each mic are shown as separate waves.
2. start with both mics next to speaker, then slowly move 1 away until the 2 waves are aligned on display, but have moved exactly 1 wavelength apart.

Question 8

Oscilloscope practical 2

Answer 8

3. measure distance between mics, find 1 wavelength.
4. use formula to find speed of sound waves passing through air-frequency is what you set signal generator to.
5. speed of sound in air= 330m/s, check results match.

Question 9

Water waves practical 1

Answer 9

1. using signal generator attached to dipper of a ripple tank, you create water waves at set frequency.
2. dim lights in lab & turn on lamp. Should see wave crests as shadows on screen below tank.

Question 10

Water waves practical 2

Answer 10

3. distance between each line=1 wavelength. Measure distance between shadow lines that are 10 wavelengths apart, then divide this distance by 10 to find average wavelength.
4. use method to calculate wave speed of the waves.
5. this set up is good as it allows you to measure wavelength without disturbing waves.

Question 11

Waves on string practical 1

Answer 11

1. set up equipment. Turn on signal generator and vibration transducer. String will start to vibrate.
2. adjust frequency of signal generator until there’s a clear wave on string. Frequency you need will depend on length of string between pulley & transducer, and masses you’ve used.

Question 12

Waves on string practical 2

Answer 12

3. measure wavelength of these waves. To do this accurately: measure lengths of 4or5 half wavelengths in one go, then divide to get mean half wavelength. Then double mean to get full wavelength.
4. frequency of wave=what signal the generator is set to.
5. find speed using formula.

Question 13

Wave meeting a boundary (3 options)

Answer 13

ABSORBED by the 2nd material. Wave transfers energy to material’s energy stores. Often energy goes to thermal energy store, leads to heating.
TRANSMITTED through. Wave carries on travelling through material. Often leads to refraction.
REFLECTED. Incoming ray is sent back from second material. How echoes are created.

Question 14

Electromagnetic Waves

Answer 14

All travel at same speed through air or a vacuum.
Vibrations of electric + magnetic fields.
Travel at different speeds in different materials.
Vary in wave length (10 to the -15 to more than the 4.
Generated by a variety of changes in atoms+nuclei.

Question 15

EM wave examples

Answer 15

Camp fire transfers energy to surroundings by emitting infrared radiation. These waves are absorbed by objects + transfer energy to objects thermal store, so object warms up.
Radio waves transfer energy to KE stores of electrons in radio receivers, generates electric current.

Question 16

Refraction

Answer 16

When wave crosses boundary between 2 materials it changes speed. If wave hits boundary at an angle it changes direction - its refracted.
Wave bends towards normal if slows down, bends away from normal if speeds up.

Question 17

How much something is refracted

Answer 17

Depends on how much wave speeds up/slows down, which depends on density of the 2 materials (higher density, slower a wave travel through).
Wavelength changes when refraction happens.

Question 18

Optical density

Answer 18

Measures how quickly light travels through it - higher optical density, slower light waves travel through it.

Question 19

Ray diagrams

Answer 19

1. Draw boundary between 2 materials + the normal (the imaginary line perpendicular to where incoming wave hits boundary)
2. Draw incident ray that meets normal at boundary.
3. Angle between ray + normal is angle of incidence. Draw with protractor if given an angle.
4. Draw refracted ray on other side of boundary.
5. Angle of refraction is angle between refracted ray and the normal.

Question 20

Wave front

Answer 20

A line showing all the points on a wave that are in the same position as each other after a given no. of wavelengths. Wave crosses boundary at angle, only part of wave front crosses boundary at first.
Denser material=slower travel.
By the time whole wave front crosses boundary, faster part of it will have traveled further than slower part. Difference in distance traveled causes wave to refract.

Question 21

Uses of EM waves

Answer 21

Radio waves: bluetooth, TV and FM radio.
Microwaves: satellites (satellite TV).
Infrared: infrared cameras electric heaters.
Visible light: optical fibres.
Ultra violet: fluorescent lights, security pens.
X-rays + gamma rays: radiographers in hospitals.

Question 22

Leslie Cube practical

Answer 22

Place empty leslie cube on heat proof mat.
Boil water, fill leslie cube with it.
Cube warms up, all 4 faces should have same temp.
Hold infrared detector a set distance from 1 of vertical faces. Record amount of IR radiation it detects.
Repeat measurement for each face.
More IR radiation will be detected from black rather than white or matte surfaces rather than shiny.

Question 23

Melting wax practical

Answer 23

1. Set up equipment. 2 ball bearings stuck to one side of metal plate with solid bits of candle wax. Other side of plates face towards flame.
2. Sides of plates facing towards flame each have a different surface colour.
3. Ball bearing on black plate will fall first as surface absorbed more IR radiation - transferring more to TE store of wax. Wax on black plate melts before wax on silver plate.

Question 24

Risk of EM waves

Answer 24

Low frequency waves pass through soft tissue without being absorbed.
High frequency waves all transfer lots of energy so cause lots of damage.
UV radiation damages surface cells, lead to sunburn and skin cancer.
X-rays and gamma rays are ionising, cause gene mutation or cell destruction, even cancer.

Question 25

Radiation dose

Answer 25

Measured in sieverts. Measure is the risk of harm from body being exposed to radiation. Risk depends on total amount of radiation and how harmful the type is. 1000 millisieverts = 1 sievert

Question 26

Radiation in different parts of the body

Answer 26

CT scan uses X-rays and a computer to build up a picture of inside the patients body. If a patient has a CT scan on their chest, they are 4 times more likely to suffer damage to their genes than if they had a head scan.

Question 27

Oscillating

Answer 27

Alternating currents made up of oscillating charges. As charges oscillate, they produce oscillating electric and magnetic fields eg EM waves. Frequency wave=frequency of alternating current.

Question 28

How to make radio waves

Answer 28

With alternating current in an electrical circuit. Object where charges oscillate to create them is called a transmitter. When they reach the receiver the waves are absorbed. Energy carried by waves is transferred to electrons in material of receiver. Causes electrons to oscillate. Current has same frequency as radio wave.

Question 29

Radio waves

Answer 29

Short wave radio signals (10m-100m) can like long wave (1-10km) be received at long distances. They are reflected from ionosphere, electrically charged later in atmosphere. Blue tooth uses short wave radio waves, radio waves for TV and FM radio have v short wavelengths. Get reception, be in direct sight of transmitter.

Question 30

Microwaves

Answer 30

Comms to and from satellites use them. Must use microwaves that pass easily through our watery atmosphere. Satellite TV:signal from transmitter transmitted into space. It’s picked up by satellite receiver dish orbiting above earth. Satellite signals back to earth in diff direction. It’s received by satellite dish on ground. Slight Time delay.

Question 31

Microwave ovens

Answer 31

Microwaves need to be absorbed by water molecules in food. Microwaves penetrate up to a few cm in food before absorbed and transferring energy they carry to water molecules in food, makes it heat up. Water molecules transfer energy to rest of molecules in food by heating.

Question 32

Infrared radiation

Answer 32

Given out by all objects, hotter object, more IR. Infrared cameras detect the former and monitor temp. Detects IR, turns it into electrical signal. Displayed on a screen as a picture. Hotter=brighter image. Absorbing IR makes object hotter, so can cook food. Electric heaters heat room same way.

Question 33

Visible light

Answer 33

Used in optical fibres bc it’s easy to refract light enough so it remains in a narrow fibre. Light not easily absorbed/scattered so travels along a fibre. Optical fibres are thin glass/plastic fibres that carry data over long distances as pulses of visible light. Work bc of refraction.

Question 34

Ultraviolet radiation

Answer 34

Fluorescent lights generate UV which is absorbed and re emitted as visible light by layer of phosphorus inside bulb. Energy efficient. Under UV light, ink will glow from security pens but otherwise invisible. UV gives you a suntan but overexposure can give you skin cancer.

Question 35

X - rays

Answer 35

Pass easily through flesh but not through dense materials like bones/metal Amount of absorbed xray gives you the image. Radiographies use them + gamma rays to treat ppl with cancer. High doses kill living cells, so directed to cancer cells.

Question 36

Gamma rays

Answer 36

Used as a medical tracer: where a gamma emitting source is injected in a patient, it’s progress is followed around body. It’s well suited to this as it can pass out through body to be detected. Xrays & gamma rays can be harmful to people. Radiographers wear lead apron/ stand behind lead screen/ leave room to keep exposure to minimum.