SP4

Question 1

What is a wave?

Answer 1

A disturbance/variation travelling through a medium or vacuum and is transferring energy from any point in space to another.

Question 2

What are the two different wave types?

Answer 2

• Longitudinal waves
• Transverse waves

Question 3

How do longitudinal waves travel?

Answer 3

The energy and wave travel along the same direction as the particles vibrate.

Question 4

How do transverse waves travel?

Answer 4

The energy and wave travel at right angles to the direction that the particles vibrate/oscillate.

Question 5

What different areas do longitudinal waves show?

Answer 5

Compression: regions of high pressure due to particles being close together

Rarefaction: regions of low pressure due to particles being spread further apart

Question 6

What different areas do transverse waves show?

Answer 6

Peaks: points of maximum positive distance from rest position

Troughs: points of maximum negative distance from the rest position

Question 7

What are examples of longitudinal waves?

Answer 7

• Sound waves
• Seismic P-waves (primary/pressure waves)

Question 8

What are examples of transverse waves?

Answer 8

• Electromagnetic waves (light, microwaves, infrared)
• Water waves
• Seismic S-waves (secondary waves)

Question 9

What is the difference between transverse and longitudinal waves regarding medium?

Answer 9

A medium is necessary for longitudinal waves to propagate, while not always being necessary for transverse waves to propagate.

Question 10

What is the amplitude of a wave?

Answer 10

The maximum distance of a point on the wave from its rest position. The greater this is the more pronounced the effect of the wave.

Question 11

What is the wavelength of a wave?

Answer 11

A measure of distance between two successive peaks/crests (compressions in transverse waves) or between two troughs (rarefactions in transverse waves) in a wave.

Question 12

What is a period and its unit?

Answer 12

How much time it takes for one wave to pass a given point.
Unit: seconds (s)

Question 13

What is a frequency and its unit?

Answer 13

The number of waves passing a point each second.
Unit: hertz (Hz)

Question 14

What does frequency determine in sound and light waves?

Answer 14

Sound waves: Pitch (how high or low it sounds)

Light waves: Colour

Question 15

How can we calculate wave speed? (2 equations)

Answer 15

Wave speed (m/s) = distance (m) / time (s)
v = x × t

Wave speed (m/s) = frequency (Hz) × wavelength (m)
v = f × λ

Question 16

How do we measure water wave speeds?

Answer 16

Measure the time it takes for a wave to travel between two fixed points (such as buoys).

Question 17

How do we measure light wave speeds in air?

Answer 17

1. Two people stand at opposite ends of a field a measure distance apart
2. One person hits two cymbals to make a noise
3. The second person starts a timer when they see the cymbals hit and stops it when they hear the sound
4. Calculate the speed using v = x / t

Question 18

How can we improve the light wave speed experiment in air?

Answer 18

As the method involves human reaction time, the second person could film the first person and use the recording to calculate the time interval.

Question 19

How do we measure light wave speeds in a solid?

Answer 19

1. Suspend a metal bar loosely from a stand using thin rubber bands
2. Strike the bar with a hammer
3. Use a smartphone app to measure the frequency of the loudest sound detected when the phone is next to the bar
4. Vibration of bar causes a standing wave, the wavelength of which is twice the length of the bar
5. Calculate wave speed using v = f × λ

Question 20

What can happen when a wave travelling from one medium reaches a boundary (a different medium)?

Answer 20

It can be:
- Reflected
- Transmitted
- Absorbed
- Refracted
- Scattered

Question 21

What are the two different types of reflection?

Answer 21

Specular reflection: reflection at a definite angle from a very smooth surface

Diffuse reflection: Scattered reflection from a rough surface

Question 22

How are objects the majority of objects visible to us?

Answer 22

Due to reflecting light in a diffuse manner.

Question 23

What is the law of reflection?

Answer 23

The reflected ray lies in the plane of incidence and makes an angle (with the normal) that is equal to the angle of incidence.

Question 24

What is transmission?

Answer 24

When beams of light pass through a medium.

Question 25

What is absorption?

Answer 25

When the wave is absorbed by the medium (energy is transferred to the material).

Question 26

What is refraction?

Answer 26

Bending of a wavefront at a boundary between two media, due to a change in wave velocity.

Question 27

What happens when a light ray moves from a medium in which light travels faster to a medium in which light travels slower?

Answer 27

The light ray bends towards the normal.

Question 28

What happens when a light ray moves from a medium in which light travels slower to a medium in which light travels faster?

Answer 28

The light ray bends away from the normal.

Question 29

How do we test the refraction of a light ray?

Answer 29

1. Place a glass block on a large sheet of paper and trace around it. 2. Draw a line at the right angles to the long side of the block. This will be the normal in your ray diagram. 3. Darken the room and use a ray box to shine a ray of light diagonally into the block. 4. Use a pencil to mark the ray's path up to and beyond the block by drawing small crosses. 5. Remove the block, then use a pencil and ruler to connect the crosses and to draw the ray's path through the block. 6. Measure the angles of incidence and refraction at the point where the light leaves the block. Light bends away from the normal as it passes from glass to air, so in this case the angle of refraction will be larger than the angle of incidence. 7. Repeat with different angles of incidence. Light bends toward the normal when it passes from air to glass, so you will find the angle of refraction from air to glass is always less than the angle of incidence.

Question 30

How do sound waves travel differently in different media and why?

Answer 30

Sound travels the fastest in solids, slower in liquids and slowest in gases. This is because particles in a solid are closer together than liquids and gases.

Question 31

How do sound waves travel from a fluid to a solid?

Answer 31

1. Particles in a gas or liquid vibrate backwards and forwards as a sound wave passes. 2. When the sound reaches a solid, some of the energy it carries is reflected, some is transmitted through the solid and some is absorbed by it. 3. Sound waves cause change in pressure on the surface of the solid. 4. This causes the particles in the solid to vibrate and so the disturbance is passes from the fluid to the solid. 5. The vibrations in the solid can be passed on both as longitudinal waves and transverse waves. 6. The shape and properties of a solid (density/stiffness) determine how vibrations of different frequencies will affect it.

Question 32

What are the 6 different parts of the human ear?

Answer 32

Ear canal: Where sound waves enter the ear Eardrum: A thin membrane which vibrates due to sound waves Tiny bones: Amplify vibrations passed on to them Cochlea: Vibrations are passed on to the liquid inside the cochlea Tiny hairs in cochlea: Detect vibrations and create impulses Auditory nerve: Impulses travel along neurones in the auditory nerve to reach the brain

Question 33

What is the cochlea?

Answer 33

A coiled tube containing liquid.

Question 34

What does the cochlea do?

Answer 34

Detects different frequencies of sound reaching the ear. This range is between 20 Hz and 20 kHz.

Question 35

Describe the cochlea's membrane.

Answer 35

The membrane in the middle of the cochlea is thicker and stiffer at the base and thinner at the apex. There are thousands of hair cells along it.

Question 36

What does the cochlea's membrane do?

Answer 36

Different thicknesses of the membrane vibrate best at different frequencies. Depending on the sound wave inside the cochlea, different parts will vibrate.

Question 37

What do the hair cells along the cochlea do?

Answer 37

They detect vibrations and are connected to a neurone that sends impulses to the brain. The brain interprets signals from different neurones as different pitches of sound.

Question 38

What is an ultrasound wave?

Answer 38

Any sound wave with a frequency higher than 20 kHz.

Question 39

What is echo-sounding?

Answer 39

High frequency sound waves are reflected from an object to measure the distance to that object.

Question 40

How do fetal scans using ultrasound occur?

Answer 40

1. Ultrasound machine transmits high-frequency (1-5 MHz) sound pulses into your body. 2. Sound waves travel into your body and hit a boundary between tissues. 3. Some of the sound waves get reflected back to the machine, while some travel on further until they reach another boundary and get reflected. 4. The reflected waves are picked up by the machine. 5. The machine calculates the distance from the probe to the tissue or organ (boundaries) using the speed of sound in tissue and the time of each echo's return. 6. The machine displays the distances and intensities of the echoes on the screen, forming a two-dimensional image.

Question 41

What is an infrasound wave?

Answer 41

Any sound wave with a frequency lower than 20 Hz.

Question 42

What are seismic waves?

Answer 42

Vibrations caused by earthquakes. This energy is released due to tectonic plates moving over each other/colliding.

Question 43

Give two examples where infrasound waves are created.

Answer 43

- Earthquakes - Volcanic eruptions

Question 44

What are the two different types of seismic waves?

Answer 44

- Primary (P) - Secondary (S)

Question 45

Describe the characteristics of a seismic-P wave.

Answer 45

- Longitudinal - Can travel through solids, liquids and gases

Question 46

Describe the characteristics of a seismic-S wave.

Answer 46

- Transverse - Can only travel through solids

Question 47

How can we detect seismic waves?

Answer 47

Using a seismometer.

Question 48

What are the 4 different parts of the Earth's interior?

Answer 48

- Crust - Mantle - Outer core (liquid) - Inner core (solid)

Question 49

How are the two earthquake shadow zones created?

Answer 49

First shadow zone: Seismic-S waves being stopped entirely by the liquid core. Second shadow zone: Refraction of seismic-P waves by the liquid core.