Waves definitions

Question 1

Dsplacement

Answer 1

The distance moved from equilibrium for a point on a wave

Question 2

Amplitude

Answer 2

The maximum displacement from the equilibrium position

Question 3

Wavelength

Answer 3

The minimum distance between two points oscillating in phase, for example the distance between one peak to the next. The length of one complete wave cycle, in metres.

Question 4

Period

Answer 4

The time taken for one complete wavelength to pass a given point OR the time taken to complete one oscillation. Measured in seconds.

Question 5

Frequency

Answer 5

The number of wavelength cycles passing a given point per unit time (seconds), measured in Hertz (1 Hz = 1s-1)

f = 1/T where f = frequency (in Hz) and T = time period (in seconds)

Question 6

Progressive Wave

Answer 6

Transfer of energy as the result of oscillations of the medium through which the energy is travelling

Question 7

Longitudinal wave

Answer 7

The oscillation of particles is parallel to the direction of travel of the wave e.g. sound

Question 8

Transverse wave

Answer 8

The oscillation of particles is perpendicular to the direction of travel of the wave e.g. waves on a string, electromagnetic

Question 9

Mechanical wave

Answer 9

Energy is transferred through a medium (i.e. by the oscillations of particles)

Question 10

Phase

Answer 10

The position of an oscillating particle or field at a given time on a wave cycle, expressed in degrees or radians, where 1 full wave cycle = 360 degrees or 2π radians.

Question 11

Wave speed

Answer 11

The distance travelled by the wave per unit time

Question 12

Reflection

Answer 12

When a wave rebounds from hitting a boundary between two mediums

Question 13

Refraction

Answer 13

When a wave changes direction as it enters a new medium, due to a change in the speed of travel

Question 14

Intensity

Answer 14

The radiant power transferred per unit area (intensity = power / area). Measured in W m-2. Intensity is proportional to amplitude2

Question 15

Electromagnetic waves

Answer 15

Waves that travel by oscillation of the electromagnetic field. Electromagnetic waves are transverse waves

Question 16

Plane polarised wave

Answer 16

A transverse wave in which the oscillations are limited to only one plane

Question 17

Critical angle

Answer 17

The angle of incidence at the boundary between two media that will produce an angle of refraction of 90 degrees

Question 18

Total internal reflection

Answer 18

The reflection of all light back into the original medium when hitting a boundary between two media; the original medium will have a higher refractive index and the incidence angle at the boundary must be greater than the critical angle.

Question 19

Principle of superposition

Answer 19

When two or more waves meet at a point, they interfere and the resultant displacement is the vector sum of the individual displacements

Question 20

Coherence

Answer 20

When two or more waves or wave sources have a constant phase difference and the same frequency

Question 21

Phase difference

Answer 21

The difference in position on a wave cycle at a given time between two oscillating points, either on the same or different waves, expressed in degrees or radians, where 1 full wave cycle = 360 degrees or 2π radians

Question 22

Path difference

Answer 22

The difference in the distance travelled by two waves from their source to a specific point

Question 23

Constructive interference

Answer 23

When two or more waves that are in phase superpose and create a maximum (which is a greater amplitude than any of the individual amplitudes)

Question 24

Destructive interference

Answer 24

When two or more waves that are in antiphase, superpose and create a minimum (the resulting amplitude is smaller than any of the individual amplitudes)

Note: destructive interference does not necessarily result in zero amplitude; two waves with different amplitudes can interfere destructively and the resulting wave will have a non-zero amplitude

Question 25

Diffraction

Answer 25

The spreading of a wave after passing through a gap or around an obstacle