Waves

Question 1

What does the term wavelength mean?

Answer 1

The distance between the same points on two consecutive waves. (metre-m).

Question 2

What does the term amplitude mean?

Answer 2

The distance from equilibrium line to the crest or trough.

Question 3

What does the term frequency mean?

Answer 3

The number of waves that pass a single point per second. (Hertz-Hz).

Question 4

What does the term period mean?

Answer 4

The time taken for a whole wave to completely pass a single point.

Question 5

What does the term wave front mean?

Answer 5

The plane in which the wave travels (ie direction of the wave).

Question 6

What is the relationships within waves? (4)

Answer 6

1. Increase frequency, velocity increases
2. Wavelength increases, velocity increases
3. Period is inversely proportional to frequency
4. Smaller period, higher frequency, greater velocity

Question 7

What are transverse waves? (3)

Answer 7

1. Light, or any EM waves, seismic S waves, water waves
2. Has peaks and troughs
3. Vibrations/oscillations that travel perpendicular to the direction of the wave.

Question 8

What are longitudinal waves?

Answer 8

1. Sound waves, seismic P waves
2. Has compressions and rarefactions
3. Vibrations/oscillations that are parallel to the direction of travel

Question 9

Describe how to determine the frequency of the waves using a ripple tank (2)

Answer 9

Measure the duration of time for a wave to pass a single point.
Use frequency = number of waves/time taken

Question 10

What are some examples of how to measure sound in air? (2)

Answer 10

1. Make a noise at ~50m from a solid wall and record time for the echo to be heard, then use speed=distance/time.
2. Have two microphones connected to a datalogger at a large distance apart and record time difference between a sound passing from one to the other – then use speed=distance/time.

Question 11

What are some examples of how to measure ripples on a surface? (2)

Answer 11

1. Use a stroboscope, which has the same frequency as the water waves, then measure distance between the “fixed” ripples and use v = fλ.
2. Move a pencil along a paper at the same speed as a wavefront, and measure the time taken to draw this line and the length of the line – then use speed=distance/time.

Question 12

What is refraction?

Answer 12

When waves pass into a more optically dense medium (air to glass), the wave will be refracted at the boundary and will change direction to bend towards the normal.
The speed and wavelength decreases. Energy of a wave is constant.

Question 13

What is transmission of waves?

Answer 13

Waves will pass through transparent material. It still can refract, but the process of passing through the material and still emerging is transmission.

Question 14

What is absorption of waves?

Answer 14

If the frequency of light matches the energy levels of the electrons, light will be absorbed by the electrons and not reemitted, and over time reemitted as heat. So that frequency has been absorbed.

Question 15

What happens when sound travels through the ear? (4)

Answer 15

1. Sound waves travel inside the ear canal, and travel to the ear drum (a thin membrane), where the waves vibrate .
2. The sound waves reach the tiny bones where vibrations amplify.
3. Vibrations are then passed to the liquid inside the cochlea. Tiny hairs inside the cochlea detect these vibrations and create electrical signals called impulses.
4. Impulses travel along neurones in the auditory nerve to reach the brain.

Question 16

Describe the term “ultrasound”

Answer 16

This is a sound wave with a higher frequency than 20,000 Hz.

Question 17

What are some uses for ultrasound? (2)

Answer 17

1. Sonar - Pulse of ultrasound is sent below a ship, and the time taken for it to reflect and reach the ship can be used to calculate the depth.
2. Foetal scanning – Used to create an image of the foetus. Ultrasound waves partially reflect at each surface boundary, and bounce back by echoes. By measuring the time, it takes for these echoes to return, an image can be produced.

Question 18

Describe the term “infrasound”

Answer 18

This is a sound wave with a frequency lower than 20Hz – also known as seismic waves- there are two P and S waves and they are used to explore the earths core.

Question 19

What are P and S waves?

Answer 19

P waves are longitudinal and can pass through solids and liquids.
S waves are transverse, only passing through solids(these move slower too).

Question 20

CORE PRACTICAL: Investigate the suitability of equipment to measure speed, frequency and wavelength of a wave in a solid and fluid (6)

Answer 20

1. Set up the ripple tank, with a paper and a ruler beneath it, ensuring the ruler is perpendicular to wavefronts, using a set square.
2. Adjust ripple tank settings for clearly visible, slow waves.
3. Measure wave wavelength using the ruler, capturing a photo for stability.
4. Time 10 seconds using the stopwatch, and count wavefronts passing a fixed point, and calculate the frequency.
5. Mark two points beneath the tank that are a set distance apart, and then use the stopwatch to measure the duration it takes for one wave to travel.
6. Use the formula v = fλ to calculate wave speed using obtained wavelength and frequency values.