05 Waves

Question 1

Amplitude?

Answer 1

Maximum displacement from a central equilibrium position

Question 2

Frequency?

Answer 2

The number of waves per second passing a point

Question 3

Wave period?

Answer 3

The time for one wave to pass a point

Question 4

Wave speed?

Answer 4

The velocity at which a wave front moves

Question 5

Wavelength?

Answer 5

Distance between one wave crest and the next

Question 6

Wavefront?

Answer 6

A line joint points on a wave which are all in phase

Question 7

Transverse waves?

Answer 7

Oscillate perpendicular to the direction of travel

Question 8

Longitudinal wave?

Answer 8

Oscillations parallel to direction of travel so that a compression is followed by a rarefraction

Question 9

Superposition

Answer 9

The net displacement of the medium at any point in space or time
Is simply the sum of the individual wave displacements

Question 10

What conditions are needed to produce a steady interference pattern (COHERENT WAVES)?

Answer 10

Same frequency
Similar amplitude
Constant phase relationship

Question 11

Coherence?

Answer 11

Waves with the same frequency and constant phase difference

Question 12

Path difference?

Answer 12

For 2 waves starting from different points and arriving at the same point, the path difference is the difference in the length travelled by each wave (m).

Question 13

In-Antiphase?

Answer 13

When the phase difference between two waves is 180º or π radians

Question 14

In-Phase

Answer 14

When the phase difference between two waves is 0º or 0 radians

Question 15

Phase difference?

Answer 15

The difference in phase (measures in º or radians)
It can be seen as the amount by which one wave lags behind the other

Question 16

Standing wave?

Answer 16

A wave that stores energy instead of transferring it.
A common example is a string fixed at both ends.
They are formed by a wave propagating and being reflected so that it comes into superposition with itself.

Question 17

Explain how a standing wave is set up on a string (6 marks)

Answer 17

• 2 waves travelling in opposite directions
• wave reflects and superposes itself
• constructive interference- ANTINODES
• destructive interference- NODES
• antinodes = max displacement
• nodes = no displacement

Question 18

Things to mention for a 6 marker on polarisation

Answer 18

• light from source is unpolarised
• intensity of the light
• no light passes when the filter is rotated 90º as the plane is now perpendicular to the light
• a COMPONENT of the light intensity can pass through
• when the filter is rotated at 0º or 180º, the plane of polarisation is aligned and light passes at full intensity
• absorb perpendicular components, transmit parallel components

Question 19

Define plane polarised

Answer 19

Transverse waves in which the direction of oscillations occur in a single plane and are perpendicular to the direction of propagation

Question 20

Polarisation definition

Answer 20

The process by which the oscillations are made to occur in one plane only
This plane includes the direction of travel of the wave

Question 21

What are 3 ways we can polarise light?

Answer 21

Polaroid filter
Reflecting light off a surface
Light scattering through the atmosphere

Question 22

What happens to the intensity of light if a Polaroid is used on unpolarised light

Answer 22

The intensity will reduce by half

Question 23

What happens to microwaves when you have vertical

Question 24

Huygen’s principle

Answer 24

As waves pass through a gap, the SPREAD OUT
Each point on the wave front acts as a source of new waves

Question 25

Things to mention for photon model of light (and if they are making you compare to waves)

Answer 25

- one photon for one electron - photon’s energy depends on frequency, E=hf - there is a minimum threshold frequency - work function (if photon energy greater than φ, electrons emitted) - whereas for waves, energy could build up - meaning any frequency should work but that doesn’t happen

Question 26

Things to mention for electron diffraction and structure of crystalline graphite (or any crystal)

Answer 26

- diffraction pattern formed - electrons behave as waves - as speed/ momentum increases, the circles get smaller - nλ = d sinθ ; justifies that as θ decreases, λ decreases - refer to λ = h/p ; justifies that as speed/momentum increases, λ decreases - the crystal has a layered structure

Question 27

What are the displacements for compressions and rarefractions in longitudinal waves?

Answer 27

They both occur at regions of ZERO displacement

Question 28

When talking about why is there a bright light on a diffraction pattern, mention:

Answer 28

- the waves meet IN PHASE - CONSTRUCTIVE interference occurs - PATH DIFFERENCE is ZERO

Question 29

Absorption of a photon does what?

Answer 29

Excites the electron and causes it to move up energy levels

Question 30

How can a photon be emitted from an atom?

Answer 30

When the electron falls from one energy level to a lower one

Question 31

Explain what is meant by the particle nature of light

Answer 31

Light consists of photos These are discrete packets of light