Chapter 4

Question 1

What is a wave?

Answer 1

• A periodic disturbance and is continuous

- Something that has travelled away from equilibrium position

Question 2

How would you classify a mechanical wave?

Answer 2

Some physical material is being disturbed

Question 3

Give some examples of mechanical waves

Answer 3

Sound waves within water or air, seismic waves

Question 4

How would you classify an electromagnetic wave?

Answer 4

Disturbance in electric or magnetic fields. No matter or particles are required.

Question 5

Which of mechanical and electromagnetic waves can travel through a vacuum?

Answer 5

Electromagnetic

Question 6

Give examples of electromagnetic waves

Answer 6

Radio, microwave, infrared, visible, ultraviolet, x-ray, gamma rays

Question 7

How would you classify a transverse wave?

Answer 7

A disturbance which creates the wave. Oscillations are moving perpendicular to the direction of energy transfer

Question 8

How would you classify a longitudinal wave?

Answer 8

The disturbance creates the wave. Oscillations are moving parallel to the direction of energy transfer

Question 9

What are compressions in a wave?

Answer 9

Where the particles in a wave are closer together

Question 10

What are rarefractions in a wave?

Answer 10

Where the particles in a wave are further apart

Question 11

With compressions are rarefractions, which has a higher pressure?

Answer 11

• Compressions have a higher pressure

- Rarefractions have a lower pressure

Question 12

Which type of waves can be polarised?

Answer 12

Transverse waves

Question 13

How does polarisation work?

Answer 13

A transverse wave passes through a polaroid, and the polaroid only allows displacement from equilibrium in one direction, and the plane is defined

Question 14

What is the direction of displacement like in an unpolarised wave?

Answer 14

In all directions

Question 15

Describe the graph of the intensity of signal against angle of rotation for: The unpolarised ray passing through 2 polaroids, and the 2nd one being rotated

Answer 15

0 deg - full intensity
90 deg- no intensity
180 deg - full intensity
270 deg - no intensity

Question 16

On a graph, what is the difference between time period and frequency?

Answer 16

Time period is the duration of one cycle

Frequency is the number of cycles in one second

Question 17

What is a radian?

Answer 17

Unit for measuring an angle

Question 18

What is the unit for radians?

Answer 18

It has none, it is a ratio

Question 19

How many pi radians are in 360 degrees?

Answer 19

2 pi

Question 20

What are the 2 situations that you would deal with phase difference?

Answer 20

• Looking at the phase difference between 2 points on the same wave
• Have 2 waves, look at phase difference at the point they meet (interference)

Question 21

How would you measure the phase difference between 2 points on the same wave?

Answer 21

Measure lamba, and the distance between 2 points.
d/lamba gives fraction of the wave.
d/l x 2 pi = phase difference in radians
d/l x 360 = phase difference in deg

Question 22

In refraction, from less dense -> more dense mediums, how does speed and wavelength change?

Answer 22

Speed and wavelength decrease

Question 23

In refraction, from more dense -> less dense mediums, how does speed and wavelength change?

Answer 23

Speed and wavelength increase

Question 24

What are wavefronts?

Answer 24

Points in a wave that have the same phase. They are perpendicular to the direction of travel

Question 25

What is superposition?

Answer 25

When waves pass through each other, and combine for an instant

Question 26

What does the superposition of waves look like for 2 waves that pass through each other and are in phase?

Answer 26

The amplitude and trough doubles - Constructive interference

Question 27

What does the superposition of waves look like for 2 waves that pass through each other and are out fo phase?

Answer 27

The amplitudes and troughs cancel out, giving a flat line - Destructive interference

Question 28

What is the path difference of 2 waves?

Answer 28

Path difference is the difference between the lengths of two paths.

Question 29

What must be true about the wavelengths for constructive path difference?

Answer 29

The difference between paths is a multiple of the wavelength

Question 30

What must be true about the wavelengths for destructive path difference?

Answer 30

The difference between paths is not a multiple of the wavelength

Question 31

Define interference

Answer 31

Formation of points of cancellation or reinforcement where 2 coherent waves pass through each other

Question 32

When are 2 sources of anything coherent?

Answer 32

2 sources of wave are coherent if they emit waves with a constant phase difference

Question 33

What are oscilloscopes?

Answer 33

Devices that can measure voltages very accurately

Question 34

What can you measure with a cathode ray oscilloscope?

Answer 34

Time period, amplitude and time events