Waves and Optics

Question 1

Mechanical Wave

Answer 1

A mechanical wave travels through a medium.

Question 2

Progressive Wave

Answer 2

A progressive wave transfers energy without transferring matter.

Question 3

Maximum Destructive Inteference

Answer 3

Destructive interference is when the resultant wave has a smaller amplitude than the individual waves. Maximum destructive interference occurs when a peaks meets a trough.

Question 4

Diffraction

Answer 4

Diffraction is the spreading of a wave into the geometrical shadow of an object.

Question 5

Coherence

Answer 5

Two waves are coherent if they have a constant phase difference (this also means they must have the same frequency).

Question 6

Longitudinal Wave

Answer 6

The particles of the medium vibrate in the same direction as the wave’s propagation.

Question 7

Maximum Constructive Interference

Answer 7

Constructive interference is when the resultant wave has a larger amplitude than the individual waves. Maximum constructive interference occurs when two peaks or two troughs meet.

Question 8

Transverse Wave

Answer 8

The particles of the medium vibrate perpendicular to the direction of the wave’s propagation.

Question 9

Principle of Superposition

Answer 9

When two or more waves meet at a point, the resultant
displacement is the algebraic sum of the displacements
of the individual waves.

Question 10

Node/Antinode for a Standing Wave

Answer 10

At a node maximum destructive interference occurs so the wave has 0 amplitude. At an anitnode maximum constructive interference occurs so the wave has maximum amplitude.

Question 11

What is represented by a wavefront? What is represented by a ray? What is the relationship between a wavefront and a ray?

Answer 11

A wavefront highlights parts of the wave that are in phase. A ray highlights the direction of energy transfer of a progressive wave. Rays are always perpendicular to wavefronts.

Question 12

Plane-Polarised Wave (and similarly an unpolarised wave)

Answer 12

A plane-polarised EM wave consists of waves which only oscillate in one plane of oscillation. (An unpolarised EM wave consists of many waves which oscillate in different, randomly orientated planes of oscillation)

Question 13

Rayleigh Criterion

Answer 13

Two images are just resolved if the first minimum of one diffraction pattern coincides with the central maximum of the other.

Question 14

Standing/Stationary Wave

Answer 14

In a standing wave the oscillations do not propagate but remain stationary. There is no net transfer of energy.

Question 15

Wavelength

Answer 15

The shortest distance between two points that are in phase.

Question 16

Phase

Answer 16

A measure of how far along in the cycle a wave is

Question 17

Phase change of reflected wave:

1. At fixed end
2. At free end
3. When entering a slower medium
4. When leaving a slower medium

Answer 17

1. pi
2. 0
3. pi
4. 0
   Note: for last two the transmitted wave has no phase change. When leaving a slower medium the transmitted wave can have a larger amplitude (depends on size of reflected wave).