Waves

Question 1

Define the term ‘progressive wave’

Answer 1

A wave which transfers energy from one place to another with a wave front which travels through the material

Question 2

What is a longitudinal wave?

Answer 2

Waves which the particles oscillate parallel to the direction of energy transfer
There are rarefactions & compressions

Question 3

What area are rarefactions & compressions found in?

Answer 3

Rarefactions = low pressure
Compressions-high pressure

Question 4

What is a transverse wave?

Answer 4

Waves where particle oscillation are perpendicular to direction of energy transfer

Question 5

Example of longitudinal waves

Answer 5

P-waves, sound wave, ultrasound

Question 6

Example of transverse waves

Answer 6

Electromagnetic waves, s-waves

Question 7

Define frequency

Answer 7

The number of waves passing through a point per second

Question 8

Units of frequency?

Answer 8

Hertz (Hz) or s^-1

Question 9

Define wavelength

Answer 9

The distance between two adjacent corresponding points (e.g peaks) on a wave

Question 10

Define amplitude

Answer 10

The maximum displacement of the wave from its equilibrium position.

Question 11

Time period equation?

Answer 11

T = 1/f

Question 12

What is the phase difference of a wave and what is it measured in?

Answer 12

The amount one wave lags behind another as s a proportion of the wavelength. Measured in degrees or radians

Question 13

What do each of the ‘axes’ on an oscilloscope measure?

Answer 13

Vertical divisions: voltage /amplitude of the wave
Horizontal divisions: time (can be used to find time period/frequency)

Question 14

Define refraction

Answer 14

Refraction is when a wave bends at a boundary between two materials due to the difference in density causing it to speed up or slow down

Question 15

True or false: A wave can either be refracted or reflected at a boundary, but never both

Answer 15

False, at low angle of incidence most will be refracted, but some will reflect

Question 16

What happens when a wave is refracted from less dense to a more dense medium?

Answer 16

Light bends towards the normal

Question 17

What happens when a wave is refracted from more dense to a less dense medium?

Answer 17

Light bends away from the normal

Question 18

Why does the change in direction occur when waves are retracted into A new medium?

Answer 18

Change in speed occurs, denser mediums will slow down rays

Question 19

Equation to calculate refractive index?

Answer 19

N=c/v

Question 20

Snells law equation?

Answer 20

Refractive index 1 x angle theta 1 = refractive index 2 x angle theta 2

Question 21

True or false: diffraction is most noticeable when the wavelength is much larger than the gap the wave is travelling through

Answer 21

False. The most diffraction is seen when the gap and the wave length are the same size.it the wavelength is much bigger the waves will be mostly reflected

Question 22

Can all waves be polarised?

Answer 22

No. Only transverse waves

Question 23

What is the difference between a polarised and unpolarised wave?

Answer 23

Polarised waves only contains waves oscillating along one axis, unpolarised waves can be oscillating in any perpendicular direction to the axis of energy transfer

Question 24

How is intensity defined din terms of power?

Answer 24

Intensity is power/area

Question 25

How are intensity and amplitude related?

Answer 25

Intensity is proportional to amplitude squared

Question 26

True or false: all electromagnetic waves have the same time period?

Answer 26

False. They all travel at the same speed-but waves their wavelengths -frequencies time and periods vary

Question 27

How fast do electromagnetic waves travel in a vacuum?

Answer 27

3x10^8 m/s

Question 28

True or false: The magnetic field & the electric field in an electromagnetic wave are parallel to each other.

Answer 28

False. They are at right angles to each other

Question 29

Put the following in order from highest to lowest frequency: X-rays, radio, micro, UV visible

Answer 29

X-rays, UV, visible, Micro, radio

Question 30

What should microwaves be polarised with?

Answer 30

A metal grid as the wavelength of microwaves is sufficiently larger than the polarising filter

Question 31

What is meant by the refractive index of a material?

Answer 31

The measure of how fast light travels in a material compared to its speed in a vacuum

Question 32

A beam of shone light is shone at a boundary between air & glass. As the angle of incidence is increased from 0 to 90 degrees, what would you see?

Answer 32

A T 0° all of the light would pass into the material along the normal. The light would then be seen to be refracted (the angle to the normal in the glass would be smaller than the incident angle ) eventually the light would bend so much it would start to be refracted back

Question 33

What is the name given to the angle of incidence at which light will reflect off a boundary rather than refracting in the medium?

Answer 33

The critical angle

Question 34

Equation to find critical angle?

Answer 34

Sinc= 1/n

Question 35

What is the name given to what happens to light at angles greater than the critical angle?

Answer 35

Total internal reflection.

Question 36

What happens in an unpolarised wave?

Answer 36

Vibrations occur in multiple directions perpendicular to propagation

Question 37

What happens in a polarised wave?

Answer 37

Vibrations are confined to a single plane

Question 38

What happens to waves with two parallel polarisation filters?

Answer 38

Maximum intensity

Question 39

What happens to waves with two perpendicular polarisation filters?

Answer 39

Minimum intensity (zero)

Question 40

What happens if one polarisation filter is 45° to the other?

Answer 40

Only a certain component can go through so intensity is less

Question 41

What is the speed of sound in air?

Answer 41

330m/s

Question 42

Describe how an oscilloscope works

Answer 42

1. Electrons are emitted from the hot cathode,directed through the control grid and accelerate to the anode 2. The electron beam is deflected vertically by the Y-plates 3. The p.d on the X-plates deflects the electron beam so that the spot on the screen moves horizontally in a sweeping motion

Question 43

What does an oscilloscope measure?

Answer 43

X-axis= time Y-axis=voltage

Question 44

How does optical fibres transmit digital signals?

Answer 44

Total internal reflection

Question 45

What do optical fibres consist of?

Answer 45

High refractive index core surrounded by a lower refractive index cladding.

Question 46

How does optical fibres work?

Answer 46

Higher refractive core surrounded by a lower refractive index cladding so light pulses travel along the core, confined by total internal reflection at the core-cladding boundary.

Question 47

What does the optical fibres small diameter ensure?

Answer 47

The angle of incidence remains greater than the critical angle even when the fibre bends.