Waves

Question 1

Amplitude

Answer 1

The maximum displacement from equilibrium of an oscillating object. For a transverse wave, it is the distance from the middle to the peak of the wave.

Question 2

Coherent

Answer 2

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

Question 3

Critical angle

Answer 3

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

Question 4

Cycle

Answer 4

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

Question 5

Diffraction

Answer 5

The spreading of waves when they pass through a gap or round an obstacle.
X-ray diffraction is used to determine the structure of crystals, metals and long molecules. Electron diffraction is used to probe the structure of materials. High-energy electron scattering is used to determine the diameter of the nucleus.

Question 6

Diffraction grating

Answer 6

A plate with many closely ruled parallel slits on it.

Question 7

Dispersion

Answer 7

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

Question 8

Electromagnetic radiation

Answer 8

An electric and magnetic wavepacket or photon that can travel through free space

Question 9

Electromagnetic wave

Answer 9

An electric and magnetic wavepacket or photon that can travel through free space

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

…of an oscillating object is the number of cycles of oscillations per second; f = 1/T.

Question 13

Fundamental mode of vibration

Answer 13

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

Question 14

Interference

Answer 14

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

Question 15

Laser

Answer 15

Device that produces a parallel coherent beam of monochromatic light

Question 16

Longitudinal waves

Answer 16

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

Question 17

Modal dispersion

Answer 17

The lengthening of a light pulse as it travels along an optical fibre, due to rays that undergo less total internal reflection

Question 18

Node

Answer 18

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

Question 19

Optical Fibre

Answer 19

A thin flexible transparent fibre used to carry light pulses from one end to another

Question 20

Path Difference

Answer 20

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

Question 21

Period of a wave

Answer 21

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

Question 22

Phase Difference

Answer 22

In radians, for two objects oscillating with the same time period the phase difference = 2pichange in time/Time period, where change in time is the time between successive instants when the two objects are at maximum displacement in the same direction

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

Refraction

Answer 25

change of direction of a wave when it crosses a boundary where its speed changes

Question 26

Refractive index

Answer 26

(Speed of light in free space)/(speed of light in the substance)

Question 27

Sinusoidal curve

Answer 27

any curve with the same shape as a sine wave (or cosine wave)

Question 28

Spectrometer

Answer 28

instrument used to measure wavelengths of light very accurately

Question 29

Stationary waves

Answer 29

wave pattern with nodes and antinodes formed when two (or more) progressive waves of the same frequency and amplitude pass through each other.

Question 30

Superposition

Answer 30

effect of two waves adding together when they meet

Question 31

Time period or period

Answer 31

Time taken for one complete cycle of oscillations.

Question 32

Total internal reflection

Answer 32

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 a certain value known as the critical angle.

Question 33

Transverse waves

Answer 33

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

Question 34

Wavefronts

Answer 34

Lines of constant phase (e.g., wavecrests).

Question 35

Wavelength

Answer 35

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 36

X-rays

Answer 36

electromagnetic radiation of wavelength less than about 1nm. X-rays are emitted from an X-ray tube as a results of of fast-moving electrons from a heated filament as the cathode being stopped on impact with the metal anode. X-rays are ionising and the penetrate matter. Thick lead plates are needed to absorb a beam of X-rays.

Question 37

Young’s fringes

Answer 37

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