Topic 3 - Waves

Question 1

Amplitude

Answer 1

Maximum displacement of a vibrating particle; for a transverse wave, it is the distance from the middle to the peak of the wave.

Question 2

Antinode

Answer 2

Fixed point in a stationary wave pattern where the amplitude is a maximum.

Question 3

Coherent

Answer 3

Two sources of waves are coherent if they emit waves with a constant phase difference.

Question 4

Critical Angle

Answer 4

The angle of incidence of a light ray must exceed the critical angle for total internal reflection to occur.

Question 5

Cycle

Answer 5

Interval for a vibrating particle (or a wave) from a certain displacement and velocity to the next time the particle (or the next particle) that has the same displacement and velocity.

Question 6

Diffraction

Answer 6

Spreading of waves on passing through a gap or near an edge.

Question 7

Diffraction grating

Answer 7

A plate with many closely-ruled parallel slits on it.

Question 8

Dispersion

Answer 8

Splitting of a beam of white light by a glass prism into colours.

Question 9

Electromagnetic wave

Answer 9

A wave packet or photon consisting of transverse electric and magnetic waves in phase and at right angles to each other.

Question 10

Endoscope

Answer 10

Optical fibre device used to see inside cavities.

Question 11

First harmonic

Answer 11

Pattern of stationary waves on a string when it vibrates at its lowest possible frequency.

Question 12

Frequency

Answer 12

The number of cycles of a wave that pass a point per second. Measured in Hz

Question 13

Interference

Answer 13

Formation of points of cancellation and reinforcement where two coherent waves pass through each other.

Question 14

Laser

Answer 14

Device that produces a parallel coherent beam of monochromic light.

Question 15

Longitudinal waves

Answer 15

Waves with a direction of vibration parallel to the direction of propagation of the waves.

Question 16

Matter waves

Answer 16

The wave-like behaviour of particles of matter.

Question 17

Modal dispersion

Answer 17

The lengthening of light pulse as it travels along an optical fibre, due to rays that repeatedly undergo total internal reflection having to travel a longer distance than rays that undergo fewer total internal reflections.

Question 18

Node

Answer 18

Fixed point in a stationary wave pattern where the amplitude is zero.

Question 19

Optical fibres

Answer 19

A thin flexible transparent fibre used to carry light pulses from one end to the other.

Question 20

Path difference

Answer 20

The difference in distances from two coherent sources to an interference fringe.

Question 21

Period

Answer 21

Time for one complete cycle of a wave to pass a point.

Question 22

Phase difference

Answer 22

The fraction of a cycle between the vibrations of two vibrating particles, measured in either radians or degrees.

Question 23

Plane-polarised waves

Answer 23

Transverse waves that vibrate in one plane only.

Question 24

Progressive waves

Answer 24

Waves which travel through a substance or through space if electromagnetic.

Question 25

Radian

Answer 25

Measure of an angle defined such that 2pi radians = 360 degrees

Question 26

Refraction

Answer 26

Change in direction is a wave when it crosses a boundary where it’s speed changes.

Question 27

Refractive index

Answer 27

Speed of light in free space / speed of light in the substance.

Question 28

Spectrometer

Answer 28

Instrument used to measure light wavelengths very accurately.

Question 29

Stationary waves

Answer 29

Waves pattern with nodes and antibodies formed when two or more progressive waves of the same frequency and amplitude pass though each other.

Question 30

Superposition

Answer 30

The effect of two waves adding together when they meet.

Question 31

Total internal reflection

Answer 31

A light ray travelling in a substance is totally internally reflected at a boundary with a substance of lower refractive index, if the angle of incidence is greater than the critical angle.

Question 32

Transverse waves

Answer 32

Waves with a direction of vibration perpendicular to the direction of propagation of the waves.

Question 33

Wavefronts

Answer 33

Lines of constant phase (e.g. wavecrests)

Question 34

Wavelength

Answer 34

The least distance between two adjacent vibrating particles with the same displacement and velocity at the same time (e.g. distance between two adjacent wave peaks).

Question 35

Young’s fringes

Answer 35

Parallel bright and dark fringes observed when light from a narrow slit passes through two closely spaced slits.