Waves (5)

Question 1

Wave motion

Answer 1

transfers energy and information without transferring matter.

Question 2

Transverse waves

Answer 2

oscillations are perpendicular to the direction of energy transfer, e.g. EM waves.

Question 3

Longitudinal waves

Answer 3

oscillations are parallel to the direction of energy transfer, e.g. sound waves.

Question 4

Wavelength

Answer 4

the distance between equivalent points in successive cycles (wave peaks).

Question 5

Amplitude

Answer 5

the maximum displacement from the undisturbed position (for a wave).

Question 6

Refraction

Answer 6

is the change of wave speed and direction at a boundary when a wave travels from one medium to another.

Question 7

Reflection

Answer 7

occurs when a wave bounces off a surface. The angle of reflection equals the angel of incidence.

Question 8

Total internal reflection

Answer 8

of light is the complete reflection of light at a boundary within a material that has a higher refractive index than its surroundings.

Question 9

Progressive wave

Answer 9

a wave that travels through a substance or a space, transferring energy.

Question 10

Hertz

Answer 10

the unit of frequency, equivalent to s-1.

Question 11

Period

Answer 11

the time for one complete cycle, measured in seconds.

Question 12

In phase

Answer 12

particles that move in phase move in the same direction with the same speed. The particles have the same displacement from their mean position. Particles in phase are separated by a whole number, n, of wavelengths, nλ.

Question 13

Out of phase

Answer 13

particles along a wave that move out of phase are at different points in their cycle at a particular time.

Question 14

Antiphase

Answer 14

particles in a wave that move in antiphase move in opposite directions at the same speed. The particles have opposite displacements from their mean position. Particles moving in antiphase are separated by a distance of a whole number, n, of wavelengths plus an extra half wavelength, nλ+λ/2.

Question 15

Phase difference

Answer 15

is measured as a fraction of the wave cycle between two points along a wave, separated by a distance x.
nλ+λ/2

Question 16

Mechanical waves

Answer 16

cannot travel through a vacuum, but need a medium to travel through.

Question 17

Polarisation

Answer 17

when the oscillations of the wave are confined to one plane, the wave is a polarised wave. For example, in an electromagnetic the electric field might be confined to just the vertical plane. These waves are said to be vertically polarised.

Question 18

Crossing

Answer 18

if a second polarising filter is held at right angles to the original filter, this is called crossing the filters.

Question 19

Angle of incidence, ϴ_i

Answer 19

is the angle between the incident ray and the normal.

Question 20

Normal

Answer 20

an imaginary line at right angles to the boundary between two materials.

Question 21

Angle of refraction, ϴ_r

Answer 21

is the angle between the refracted ray and the normal.

Question 22

Refractive index

Answer 22

the ratio of a wave’s speed between two materials. It is normally quoted for light travelling from a vacuum into a material.

Question 23

Critical angle

Answer 23

is the angle of refraction for which the angle of incidence is 90°.

Question 24

Optical fibre

Answer 24

is a thin glass (or plastic) fibre that transmits light.

Question 25

Step index optical fibre

Answer 25

is an optical fibre with a uniform refractive index in the core and a smaller uniform refractive index for the cladding.

Question 26

Material dispersion

Answer 26

is the spreading of a signal caused by the variation of refractive index with wavelength.

Question 27

Pulse broadening

Answer 27

occurs when the duration of a pulse increases as a result of dispersion in an optical fibre.

Question 28

Modal dispersion

Answer 28

is the spreading of a signal caused by rays taking slightly different paths in the fibre.

Question 29

Absorption

Answer 29

occurs when energy from a signal is absorbed by the optical fibre in which it travels.