Waves (M4)

Question 1

Fundamental frequency

Answer 1

The lowest frequency an object (eg a string) can vibrate at.

Question 2

Harmonic

Answer 2

An integer multiple of the fundamental frequency

Question 3

Stationary wave

Answer 3

Two progressive waves with the same frequency (and ideally the same amplitude) travelling in opposite directions are superposed. It remains in a constant position with no net energy transfer.
Characterised by nodes and antinodes.

Question 4

Node

Answer 4

A point on a stationary wave where displacement is always zero, therefore amplitude and intensity are zero.

Question 5

Antinode

Answer 5

A point on a stationary wave of greatest amplitude and therefore intensity.

Question 6

Interference

Answer 6

Superposition of two progressive waves from coherent sources to produce a resultant wave with a displacement equal to the sum of the individual displacements from the two waves.

Question 7

Constructive interference

Answer 7

Superposition of two waves in phase so that the resultant wave has greater amplitude than the original waves.

Question 8

Destructive interference

Answer 8

Superposition of two waves in antiphase so that the waves cancel each other out and the resultant wave has a smaller amplitude than the original waves.

Question 9

Phase difference

Answer 9

The difference between the displacements of particles along a wave, or two different waves.
Measured in degrees or radians, with each complete cycle, or a difference of one wavelength representing 360° or 2pi radians.

Question 10

Path difference

Answer 10

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

Question 11

Young’s double slit equation

Answer 11

L = ax/D
L = wavelength
a = separation between slits
x = separation between fringes
D = distance between the screen and the slits
a«D

Question 12

Principle of superposition of waves

Answer 12

When two waves of similar types meet at a point, the resultant displacement at that point is equal to the sum of the displacements of the individual waves.

Question 13

Coherent

Answer 13

Two wave sources, or waves, that have a constant phase difference and the same frequency.

Question 14

Monochromatic

Answer 14

Light of a single frequency

Question 15

Plane polarised

Answer 15

Description of a transverse wave in which the oscillations are limited to only one plane.

Question 16

Partially polarised

Answer 16

Description of a transverse wave in which there are more oscillations in one particular plane, but the wave is not completely plane polarised.
Occurs when transverse waves reflect off a surface.

Question 17

Unpolarised

Answer 17

Description of a transverse wave in which the oscillations occur in many planes.

Question 18

Electromagnetic waves

Answer 18

Transverse waves with oscillating electric and magnetic components that do not need a medium to travel through.
They all travel at the speed of light through a vacuum.

Question 19

EM wavelengths

Answer 19

Radio: >10^6 - 10^-1
Microwaves: 10^-1 - 10^-3
Infra red: 10^-3 - 7x10^-7
Visible light: 7x10^-7 - 4x10^-7
UV: 4x10^-7 - 10^-8
X-ray: 10^-8 - 10^-13
Gamma: 10^-10 - <10^-16

Question 20

Refractive index

Answer 20

A measure of the bending of a light ray when passing through one medium into another.

Question 21

Total internal reflection

Answer 21

When all the light is reflected back into the original medium. There is no light energy refracted out of the original medium.

Question 22

Amplitude

Answer 22

Maximum displacement from the equilibrium position.
Symbol: A
Unit: m

Question 23

Wavelength

Answer 23

Maximum distance between two points in phase on adjacent waves, for example one peak to the next or one compression to the next.
Symbol: lambda
Unit: m

Question 24

Frequency

Answer 24

The number of wavelengths passing a given point per unit time.
Symbol: f
Unit: Hz

Question 25

Period

Answer 25

The time taken for a wave to move one whole wavelength past a given point.
Symbol: T
Unit: s

Question 26

Progressive wave

Answer 26

An oscillation that travels through matter (and in some cases through a vacuum). All progressive waves transfer energy but not matter.

Question 27

Longitudinal wave

Answer 27

A wave where oscillations are parallel to the direction of energy transfer.

Question 28

Transverse wave

Answer 28

A wave where the oscillations are perpendicular to the direction of energy transfer.