Waves definitions

Question 1

Longitudinal Wave

Answer 1

A wave in which the particles move back and forth in the direction of wave
travel, e.g. sound waves.

Question 2

Transverse Wave

Answer 2

A wave in which the particles move perpendicular to the direction of wave
travel e.g. water waves.

Question 3

Crest

Answer 3

The top point (peak) of a wave.

Question 4

Trough

Answer 4

The bottom point of a wave.

Question 5

Amplitude

Answer 5

The vertical distance from the axis to the top of the wave (crest) or bottom of
the wave (trough). It is also half the vertical height of the wave.

Question 6

Wavelength

Answer 6

The horizontal distance from one crest to the next crest, one trough to the next
trough or one point on a wave to the same point on the next wave.

Question 7

Travelling Wave

Answer 7

A transverse wave that can be represented mathematically with an equation.

Question 8

Phase Difference

Answer 8

A measure of how much one wave lags behind another, or one point lags
behind another on the same wave.

Question 9

Stationary (Standing)
Wave

Answer 9

Formed by the constructive interference of two waves, of the same frequency
and amplitude, travelling in opposite directions.

Question 10

Node

Answer 10

A point on a stationary wave where the amplitude is zero.

Question 11

Antinode

Answer 11

A point on a stationary wave where the amplitude is a maximum.

Question 12

Interference

Answer 12

Occurs when coherent waves overlap.

Question 13

Coherence

Answer 13

When waves have a constant phase difference between them.
The waves will also have the same frequency, wavelength and speed.

Question 14

Phase

Answer 14

Used to describe how ‘in tune’ two waves are when overlapping.

Question 15

Constructive
Interference

Answer 15

When two waves of equal amplitude meet in phase, they combine to form a
wave of twice the amplitude.

Question 16

Destructive
Interference

Answer 16

When two waves of equal amplitude meet out of phase, they combine to form
a wave of zero amplitude.

Question 17

Path Difference

Answer 17

The difference in distance travelled by waves from different coherent sources.

Question 18

Maximum/Maxima

Answer 18

A point/points of constructive interference.

Question 19

Minimum/Minima

Answer 19

A point/points of destructive interference.

Question 20

Order Number (m)

Answer 20

An integer (whole number) value which describes the point on the interference
pattern (screen) you are dealing with.

Question 21

Division of Amplitude

Answer 21

Interference of light produced by thin (oil) films, coated camera lenses and thin wedge interference.

Question 22

Division of Wavefront

Answer 22

Interference of light produced by Young’s double slit experiment.

Question 23

Geometric Path Length

Answer 23

The distance travelled by a wave through a material, not taking into account the refractive index of the material.

Question 24

Optical Path Length

Answer 24

The distance travelled by a wave through a material, taking into account the
refractive index of the material.

Question 25

Optical Path Difference

Answer 25

The difference in optical path lengths.

Question 26

Blooming of Lenses

Answer 26

Placing a special thin coating such as magnesium fluoride on camera or
binocular lenses to ensure that maximum light is transmitted through the lens.

Question 27

Fringes

Answer 27

The successive pattern of bright and dark bands in an interference pattern.

Question 28

Fringe Spacing (Δx)

Answer 28

The distance between adjacent fringes of the same type (i.e. bright or dark) in
an interference pattern.

Question 29

Polarisation

Answer 29

An effect most commonly observed when using polarising lenses in sunglasses
which reduces the glare from reflective surfaces such as water or glass.
Light is said to be linearly plane polarised when the electric field oscillations
occur in only one plane.

Question 30

Polariser

Answer 30

Allows light to pass through in one plane only.

Question 31

Analyser

Answer 31

Often used together with a polariser. It is simply a second polariser.
If placed in front of a polariser and rotated to 90 ̊ , it will block the light
completely.

Question 32

Brewster’s Angle

Answer 32

The angle of incidence which causes the reflected light to be fully plane-
polarised.
This occurs when there is an angle of 90 ̊ between the reflected and refracted
rays.

Question 33

Absolute Refractive
Index

Answer 33

A number greater than or equal to 1 which indicates a material’s ability to
refract light.
It is also the ratio of the speed of light in a vacuum to the speed of light in the
medium.