Topic 4 - Waves Flashcards

1
Q

Waves basics

What do waves do?

A

Waves transfer energy from one place to another without transferring any matter.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Waves basics

What happens when a wave travels through a medium?

A

The particles of the medium vibrate and transfer energy between each other e.g. if you drop a twig in a stagnant pool the ripples don’t carry the twig away as the water only moves up and down.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Waves basics

Define amplitude

A

Maximum displacement from rest position of a wave that measures the amount of energy the wave transfers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Waves basics

Define trough

A

The lowest point of the wave

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Waves basics

Define crest

A

The highest point of the wave

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Waves basics

What is the rest position of a wave

A

The point of zero displacement on a wave (undisturbed)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Waves basics

What is the wavelength of a wave

A

The distance from trough to trough or crest to crest measured in metres

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Waves basics

Define frequency

A

Number of oscillations a wave completes every second (Hz). 1 Hz is 1 wave per second

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Waves basics

Define period

A

The time it takes for one oscillation to occur. (seconds)
Period = 1 / frequency

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Waves basics

Define wave speed

A

Wave speed (m/s) = distance (m) / time (seconds)

How far the wave travels every second

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Transverse and longitudinal

What is a transverse wave?
Give examples

A

A wave where the oscillations are perpendicular to the direction the wave travels/perpendicular to the direction of energy transfer.

Examples in include:
* All electromagnetic waves
* S-waves
* Water waves

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Transverse and longitudinal

What is a longitudinal wave?
Give examples

A

A wave where the oscillations are parallel to the direction the wave travels

Examples include:
* Sound waves
* P-waves

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Measuring wave speed

How do you measure the speed of sound using on oscilloscope?

A
  1. Set up the oscilloscope so the detected waves at each microphone are shown as separate waves.
  2. Start with both microphones next to the speaker then move one away until the 2 waves are alinged again but 1 wavelength apart.
  3. Measure distance between 2 microphones which = wavelength.
  4. Use formula velocity = frequency * wavelength (the frequency = frequency set in the signal generator)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Measuring speed of water waves

How do you measure the speed of water ripples?

A
  1. Using a signal generator attached to the dipper of a ripple tank you can create water waves at a set frequency.
  2. Dim the lights in the room and turn on a strobe light above the ripple tank which will create a wave pattern shadow below.
  3. Alter the frequency of the strobe light so the shadows appear to be still
  4. Distance between 2 shadows = wavelength (λ)
  5. Measure to find average
  6. Use velocity (m/s) = frequency (Hz) * wavelength (λ) to calculate the speed
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Waves at boundaries

What are the 3 possible outcomes when a wave reaches a boundary between 2 materials?

A
  • Absorbed - The wave transfers energy into the material’s energy stores (often thermal)
  • Transmitted - The wave carries on travelling through the material (leads to refraction)
  • Reflection - The wave is ‘sent back
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Why would different substances and waves do one of the three?

(Absorption, transmission, reflection)

A

Depends on the wavelength and the properties of the material

17
Q

Refraction

What affects a waves speed?

A

Density of the substance it is travelling through

18
Q

Refraction

What happens when a wave hits a boundary at an angle?

A

Its change in speed causes a change in direction

19
Q

Refraction

As the change in speed increases, how does this impact the change in direction?

A

Increases change in direction

20
Q

Refraction

What is a normal?

A

An imaginary perpendicular line to the boundary

21
Q

Refraction

Fill in the gaps:

The wave bends ??? the normal if it slows down and ??? from the normal if it speed up

A

The wave bends towards the normal if it slows down and away from the normal if it speed up

22
Q

Refraction

What type of wave usually goes slower in denser materials?

A

EM (electromagnetic) waves such as light

23
Q

Refraction

Pick the correct answer:
Short/long wavelengths bend more when crossing a boundary

A

Short wavelengths bend more when crossing a boundary

24
Q

Refraction

What happens to the wavelength of a wave as it is slowed down?

A

The wavelength decreases

25
Q

Critical angles

What is total internal reflection?

A

When a wave crosses a boundary it is reflected back into a material

26
Q

Critical angles

When does total internal reflection occur?

A

When the angle of incidence > the critical angle

27
Q

Critical angles

What is the critical angle

A

The angles where a ray travelling in a tranparent medium can hit the boundary without being reflected in the medium

28
Q

Sound waves

What are sound waves caused by?

A

Vibrating objects

29
Q

Sound waves

Are sound waves transverse or longitudinal

A

Longitudinal waves

30
Q

Sound waves

What happens when a sound wave passes through a solid?

A

Particles in the solid vibrate

31
Q

Sound waves

From slowest to fastest, state the speed of sound waves in the three states of matter

(solid, liquid,gas)

A
  1. Gas
  2. Liquid
  3. Solid

This is because longitudinal waves travel through particle collision, and because solids have the highest density, sound travels faster in solids, making gas slowest due to lowest density of particles.

32
Q

Sound waves

What happens to the frequency when it travels through a different medium?

A

The frequency of the sound wave doesn’t change

33
Q

Sound waves

What is the range of frequencies that the human ear can detect (hear)?

A

20 - 20,000Hz

Anything below 20 Hz = Infrasound
Anyhting above 20,000 Hz = Ultrasound

34
Q

The human ear

How does the ear work?

A

Sound waves that reach the eardrum cause it to vibrate. The vibrations are passed through your earbone to the semicircular canals and into the cochlea.
The cochlea converts these vibrations into electrical signals that are sent to the brain and are interpreted by it as sound.

Below is a link that contains an annotated diagram of the ear. Copy it into google to view:
[https://www.savemyexams.com/a-level/physics/aqa/17/revision-notes/10-medical-physics/10-2-physics-of-the-ear/10-2-1-structure-of-the-ear/]

35
Q

Using Infrasound and Ultrasound

How can ultrasound be used to look inside things?

A

Ultrasound waves can pass through the body but wehn they reach a boundary between 2 medias some of the wave is refected back which is processed by a computer to form an image.

36
Q

Using Infrasound and Ultrasound

How can ultrasound be used for sonar to locate objects in water

A

A pulse of ultrasound is sent downwards by the submarine (travelling at 1500m/s) and it takes 4 seconds to get to the sea floor and back. 4 / 2 = 2 seconds. 2 * 1500 =3,000 3000m - So the waiter is 3000m deep.

37
Q

Core Practical

Describe a practical to measure wave speed on water

A
  1. Set up a ripple tank with a ruler above the water
  2. Change the voltage at the motor until 2 waves can be seen at once (around half the length of the tank
  3. Count how many waves are formed in 10 seconds and record it
  4. Estimate wavelength using ruler. Use wavelength and frequency to find out the wave speed
38
Q

Core Practical

Describe an experiment to measure wave speed in solids?

A
  1. Suspend a metal rod hoprizontally using clamp stands and rubber bands
  2. Hit one end of the rod using a hammer and hold a frequency meter and **note down the frequency.
  3. Measure the length of the rod - The wavelength will be 2 * the rod
  4. Use the frequency and wavelength to find the speed of sound in a rod**