Topic 11: Wave Phenomena

Question 1

Principle of superposition

Answer 1

When two waves pass at a location, the resultant amplitude is the vector sum of the individual displacements.

Question 2

Standing waves

Answer 2

Standing waves occur when two identical waves travelling in opposite directions superpose. The peaks move up and down but do not progress down the wave.

Question 3

Node

Answer 3

A point on a standing wave which mains stationary due to destructive superposition.

Question 4

Anti-node

Answer 4

A point on a standing wave which oscillates at maximum amplitude.

Question 5

Standing wave and energy

Answer 5

They do not transport energy, but store it.

Question 6

Standing wave and phase

Answer 6

All the points between adjacent antinodes are in the same phase. Adjacent nodes have a phase difference of π rad.

Question 7

Standing wave in string

Answer 7

There is an antinode at the fixed end of a vibrating string. The reflected wave superposes on the incident wave.

Question 8

Standing wave in pipes

Answer 8

A standing wave can arise in air in a pipe. At an open end there is a node; at a closed end, there is an antinode.

Question 9

Fundamental mode

Answer 9

The lowest frequency mode of vibration of an oscillating system.

Question 10

Harmonics

Answer 10

The different modes of vibration of an oscillating system.

Question 11

Doppler effect

Answer 11

The change in frequency observed when a source of waves is moving relative to the observer.

Question 12

Single slit diffraction

Answer 12

Waves passing through a narrow aperture is diffracted and interference effects cause a pattern of maxima and minima.

Question 13

Double slit diffraction

Answer 13

Waves passing through two parallel slits interfere and produce maxima and minima. The separation of the fringes depends on the wavelength, slit separation and distance of the fringes from the slits.

Question 14

Resolution

Answer 14

If two sources, close to each other, can be seen as separate, we say we can resolve them.

Question 15

Rayleigh criterion

Answer 15

The minimum separation between two sources so that they can still be resolved by the observer. At the point that two sources can just be resolved, the central maximum of one source coincides with the first minimum of the other.

Question 16

Polarisation

Answer 16

When the disturbance of a wave is restricted to one plane, it is (plane)-polarised.

Question 17

Polarisation of light

Answer 17

Light can be polarised by passing it through a polarising filter, or by reflecting it from a surface.

Question 18

Brewster’s angle

Answer 18

When light reflects from a surface so that the reflected ray is at 90° to the transmitted (refracted ray), polarisation of the reflected ray is 100%. The angle of incidence in this situation is called the Brewster angle.

Question 19

Malus’ Law

Answer 19

When a ray with intensity I0 hits a polarising filter at angle ϑ, the intensity of the emerging ray, I is given by Malus’ law. I = I0 cos^2 ϑ

Question 20

Simple harmonic motion

Answer 20

Motion where the acceleration of the particle is proportional to but in the opposite direction to the displacement of the particle. Acceleration directed towards equilibrium.

Question 21

Damping

Answer 21

Reduction of amplitude, caused by an external force, resulting in transfer of energy to heat, sound etc.
OR: Energy removed from an oscillating system

Question 22

Resonance

Answer 22

Driving frequency is equal to the system’s own natural frequency