Waves

Question 1

Amplitude

Answer 1

The magnitude of the maximum displacement of the medium

Question 2

Antinode

Answer 2

Position of maximum amplitude on a standing wave

Question 3

Coherence

Answer 3

Two sources of waves are coherent if there is a constant phase difference between them

Question 4

Constructive interference

Answer 4

Occurs when multiple sources tend to superpose to increase the amplitude of a wave at a given point.
For two source interference this occurs with a path difference of n

Question 5

Destructive interference

Answer 5

Occurs when multiple sources tend to superpose to decrease the amplitude of a wave at a given point (often to zero).
For two source interference this occurs with a path difference of (n+0.5)

Question 6

Diffraction

Answer 6

The spreading out of a wavefront when it passes through a gap.

Max. diffraction when wavelength is similar to gap width
Some diffraction when wavelength is smaller than gap width
No diffraction when wavelength is larger than gap width

Question 7

Displacement

Answer 7

The distance and direction of a point in the medium from its equilibrium position

Question 8

Frequency

Answer 8

The number of complete waves passing a point per unit time or
The number of oscillations completed by a point in the medium per unit time

Question 9

Fundamental mode of vibration

Answer 9

The lowest frequency (longest wavelength) standing wave oscillation that a system can support

Question 10

Harmonics

Answer 10

Oscillations with frequencies that are integer multiples of the fundamental frequency of a system. The first harmonic is thus another name for the fundamental

Question 11

Intensity

Answer 11

Power per cross sectional unit area.

It is proportional to the amplitude² of a wave

Question 12

Interference

Answer 12

The phenomenon which may occur when two or more waves of the same type are incident upon the same point, resulting in a wave of different amplitude from the original waves

Question 13

Longitudinal wave

Answer 13

Wave in which the direction of vibration is parallel to the direction of energy transfer

Question 14

Malus’ law

Answer 14

For plane-polarised light incident on a polarizing filter, the transmitted intensity is given by:
I=Iocos²θ,
where Io is the incident intensity and theta is the angle between the plane of polarisation and the angle of the filter

Question 15

Node

Answer 15

Position of zero amplitude on a standing wave

Question 16

Path difference

Answer 16

The difference in path length measured from a wave source to a given point and path length measured from a second wave source to the same point

Question 17

Period

Answer 17

The time for one complete oscillation of a particle in the medium

Question 18

Phase

Answer 18

How ‘far through’ an oscillation a point on the wave is, from 0 to 360° or from 0 to 2π radians

Question 19

Phase difference

Answer 19

Relates to oscillation of two points on the same wave

How far ‘out of step’ one oscillation is from the other

Question 20

Plane-polarised

Answer 20

A wave in which the oscillations of the medium occur in a single plane. It is only possible to polarise transverse waves

Question 21

Principle of superposition

Answer 21

When two or more waves meet at a point

the resultant displacement is given by the vector sum of the individual displacements of the waves

Question 22

Progressive wave

Answer 22

Wave that transfers energy from one place to another as a result of oscillations

Question 23

Reflection

Answer 23

A wave ‘bounces’ off a surface formed by the boundary between two different media. The angle of incidence is equal to the angle of reflection

Question 24

Refraction

Answer 24

A wave changes speed in traversing the boundary between two different media. This leads to a change in wavelength (always) and a change in direction (unless the wave is propagating along the normal to the boundary)

Question 25

Stationary wave

Answer 25

Wave in which the medium oscillates but there is no net transfer of energy from one point on the wave to another. Formed by the superposition of two counter-propagating progressive waves

Question 26

Transverse wave

Answer 26

Wave in which the direction of vibration is perpendicular to the direction of energy transfer

Question 27

Wave speed

Answer 27

The speed of propagation of the wavefront (point of constant phase); it is equal to frequency x wavelength

Question 28

Wavelength

Answer 28

The shortest distance between two points of equal phase on the wave (e.g. distance from peak to adjacent peak or trough to adjacent trough)