Waves

Question 1

What happens when a wave travels through a medium

Answer 1

The particles of the mesium oscillate and transfer energy between each other but overall the particles stay in the same place-only energy transferred

Question 2

What is amplitude of the wave

Answer 2

The maximum displacement of a point on the wave from its undisturbed posiition

Question 3

What is wavelength

Answer 3

Distance ebtwwen the same point on two adjacent waves

Question 4

What is frequency

Answer 4

Frequency is the number or complete waves passing a certain point per second. Measured in hertz (hz) per second

Question 5

How to calculate period

Answer 5

1
T= ——-
F

Question 6

What direction do oscillations travels in tranverse waves provide examples

Answer 6

In transverse waves the oscillations are perpendicular (90°) to the direcrion of energy transfer

All electromagnetic waves (light), ripples through water, guitar string

Question 7

What direction do oscillations travels in longitudinal waves provide examples

Answer 7

In longitiudinal waves the oscillations are parallel to the direction of enrgy transfer

Sound waves in air

Question 8

How to calculate wave speed

Answer 8

V = fλ

Question 9

How do you use an oscilloscope

Answer 9

1) set the oscilloscope so the detected waves at each microphone are shown as seperate waves

2) start with both microphones next to the speaker, then slowly move one away until the two waves are aligned on the display but have moved one wavelength spart

3) Measure the distance between the microphone to find wavelength

4) Use V=fλ to find speed of the waves through the air- f is what you set the signal generator to

5) The speed of sound is 330m/s check your results to compare

Question 10

Required practical: How to measure the speed of water using a ripple tank

Answer 10

1) use a signal generator attached to the dipper of a ripple tank you can create water waves at set frequency

2) Turn off the lights and turn on a lamp. You should see the wave crests as shadows on the screen below the tank

3) The distance between each shadow line = one wavelength. Measure the distance between shadow line that are 10 wavelengths aprt then divide by 10 to find average

4) Use V= Fλ to calculate wave speed

5) The set up is suitable for investigating waves, because it alllows youn to measure the wavelength without disturbing the waves

Question 11

Required practical: How to use wave equation for waves on strings

Answer 11

1) place a signal generator on a bench with a vibration transducer to its side attached to a string in a pulley system with a hook with masses

2)Adjust the frequency of the signal generator until there is a clear wave on the string. F will depend on length between the pulley and transducer and the masses you use

3) Measure the wavelength. Best way is to measure multiple wavelengths at once using a ruler then divide by the number of wavelengths to get an mean half wavelength then double to get the full wavelength

4) Frequency depends on what the signal generator is set to

5) find speed using V = Fλ

Question 12

What happens when a wave is absorbed,transmitted or reflected

Answer 12

Absorbed: the wave transfers energy to the second materials energy store. It is often transferred to thermal.

Transmitted: waves go through the new material then carries on the travelling through the new material often leading to refraction. This is used in communications or lenses in cameras

Reflected: Incoming rays are neither absorbed or transmitted but sent back from the second material. This is how echoes are created

Question 13

Properties of EM waves

Answer 13

Transverse wave

Travel at the same speed through air ir a vacuum (space)

Vary in wavlength 10^-15 to 10^4

Range in frequencies throught the spectrum- radio low - gamma high

Travel at different speeds in different material

Question 14

All the different waves on the EM spectrum

Answer 14

Radio waves

Micro waves

Infared waves

Visible light

Ultra voilet

X-rays

Gamma rays

Question 15

Properties of radio waves

Answer 15

10^-4m

Low frequency

Question 16

Properties of gamma rays

Answer 16

10^1-15

High frequency

Question 17

What is refraction

Answer 17

1) When waves cross a boundary between two materials it changes speed

2) If waves hit along the normal only speed changes. If it hits at an angle only direction changes

3) The waves bend toward the normal (slows down)- the wave bends away from the normal (speeds up)

4) Higher the optical density the, the slower the light travels

5) wavelength only changes, frequency stays the same

Question 18

How do ray diagrams show the path of a wave

Answer 18

1) Draw a boundary between your 2 materials and the normal. It should be perpendicular (90°) to where the wave will hit the boundary.

2) Draw an incident ray that meets the normsl at the boundary

3) Angle between the incident ray and normal is the angle of incidence.

4) Draw the refracted line on the other side of the boundary

5) Angle of refraction is the angle between the refracted ray and the normal

6) If the second material is optically denser than first , the refracted ray bends towards the normal (smaller angle of refraction then the angle incidience).

If the second material is less optically dense then the first, the refracted rays bend away from the normal (angle of refraction is larger than the angle of incidence).

Question 19

How to use wave front diagrams

Answer 19

1) Wave front is a line showing all of the points on a wave that are in the same positions as each other after a given number of wavelengths

2) Wave crosses the boundary at an angle, only part of the wave front crosses the boundary at first. If its travelling into a denser material, that part travels slower then the rest of the front

3) By the whole time the whole wave front crosses the boundary, the faster the part of the wave front will have travelled further than the slower part of the wave front

4) The difference in distance travelled by the wave front causes the wave to bend

Question 20

How are radio waves made by an oscillating charge

Answer 20

1) Em waves made up by an oscillating charge and magentic field

2) alternating currents make up the oscillating charge. As the charges collide they produce oscillating electric and magnetic fields, EM waves.

3) Frequency of waves produced will equal to the frequency of alternating current.

4) A transmitter in which charges oscillate to create radio waves reach a reciever to be absorbed. The energy carried by the waves is transferred to the electrons in the material of the reciever.

5) The electrons oscillate and if the reciever is part of a complete electrical circuit, an alternsting current will be produced.

6) Current has the same frequency as the radio waves that generate it

Question 21

How are radio waves used for communication

Answer 21

Long-wave radio waves can diffract around the curved surface of the Earthand around hills,tunnels etc-radio waves can be recieved even if the reciever isn’t in line of sight

Short wave radio waves like long waves be recieved at long distances from the transmitter. They are reflected by the ionsphere-electrically chatged layer in the Eatths upper atmosphere

Bluetooth uses short wave radio waves to send data over short distances between devices.

Medium-wave signals can reflect the ionsphere, depending on atmospheric conditions

TV and FM radio transmisisons have very short wavelengths must be in direct sight of the transmitter.

Question 22

How are microwaves used by satellites and for ovens

Answer 22

The transmitter sends microwaves to pass through the water atmosphere of the Earth easily to the satellite reciever dish where it transmits a signal back to the Earth recieved by another satellite dish.

In microwave ovens, the microwaves are absorbed by water molecules in food causing the water moleucles to heat up. It then transfers energy to the rest of the molecules in the food through heating which cooks the food.

Question 23

How are infared waves used

Answer 23

Infared cameras can be used to detect infared radiation and monitor temperature. The camera detects the IR radiation and turns it info an electrical signal displayed on a screen as a picture. The hotter the object the brighter it is.

Food can be cooked by absorbing IR radiation-it gets hotter

Electrical heaters contains a long piece of wire that heats up when a current flows through. The wire emits IR radiation and the emitted radiation is absorbed by objects and the air- energy transferred by the IR waves to the thermal energy stores of an object

Question 24

How do fibre optic cables use visible light

Answer 24

Optical fibres are thin pieces of glass or plastic fibres that carry data over long distances as pulses or visible light.

This happens due to reflection - light rays are bounced back and forth until they reach at the end of the fibre.

Visible light is used because it is easy to refract light enough so it remains in the fibre and isn’t easily absorbed or scattered as it travels along the fibre.

Question 25

How are UV rays used

Answer 25

Fluorescent lights generate UV radiation, which is absorbed and re-emitted as visible light by phosphor in a bulb-energy efficient.

Security pens can mark property-under UV light it glows however remains invisble under visible light

UV radiation produces by the sun , exposure to it will give people a suntan similarly UV lamps are used in tanning salons to give an artificial tan.

Question 26

How are x-rays and gamma rays used in medicine

Answer 26

Radiographers use X-ray to check people have broken bones- they pass easily through flesh but bone and metal are denser and can’t pass through-areas where the x-rays can’t enter are white

Radiograobers yse x-rays and gamma rays to treat people with cancer. High doses of this will kill all living cells so they are carefully directed towards cancer.

Gamma radiation can be used as a medical tracer-gamma-emitting source injected into a patient and is tracked around the body.

X-rays and gamma rays are harmful so radiographers wear lead apeons and stand behind lead screens or leave the room to minimise exposure.

Question 27

Required practical: investigate emissions using a Leslie cube

Answer 27

1) place a empty leslie cube on a heat proof mat

2) Boil water in a kettle and fill the Leslie cube with boiling water- be careful with boiling water

3)Wait for the cube to warm up and hold a thermometer against each of the four vertical faces (all same temp)

4) Hold an infared detector a set distance away from one of the cube verticsl faces and record the smount of IR radiation it detects.

5) Repeat this measurment for each of the cube’s verticsl faces. Place the detetcor the same distanxe from the cube each time

6) Darker surface detect more IR radistion then whiter surfaces. Matt surfaces detect more IR radiation then shiny surfaces.

7) Repeat the experiment.

Question 28

How to investigate absorption with the melting wax trick

Answer 28

1) place two ball bearings on a side of a metal plate with solid pieces of candle wax. The other sides of these plates are then faced towards the flame of a bunsen burner

2) The different sides of the plates are facing towards the flame each have a different surface colour-matt black and silver.

3) The ball bearing on the black plate will fall first as black surfaces absorb more IR radiation-transferring more energy to the thermal energy of the wax

Question 29

How is EM radiation harmful to people

Answer 29

Em radiation can enter living cells - radio waves are harmless and pass through however high frequencies of UV,X-ray and gamma all transfer lots of enrgy and can do damage.

UV radiation can damage surface cells, sunburn and cause skin to age. May also cause blindness and increase risk of skin cancer

X-rays and gamma rays are types of ionising radiation. This causes gene mutations, cell destruction or cancer

Question 30

How to measure risk using radiation dose in sieverts

Answer 30

Using EM waves are considered heavily- benefits must outweigh health risks.

Radistion dose is the measure of risk of harm from the body being exposed to radiation

Risk depends on the total amount absorbed and type of radiation

1000mSv= 1Sv

Question 31

What is the trough and crest

Answer 31

Trough is the very bottom of a wave

Crest is the peak of the wave