LIGHT & WAVES

Question 1

the laws of reflection

Answer 1

1. the angle of incidence = the angle of reflection.

2. the incident ray, the normal at point of incidence and the reflected ray all lie in the same plane

Question 2

real image

Answer 2

formed by the actual intersection of light rays. It can be formed on a screen.

Question 3

virtual image

Answer 3

formed by the apparent intersection of light rays. It cannot be formed on a screen.

Question 4

laws of refraction

Answer 4

1. the incident ray, the normal at point of incidence and refracted ray all lie in the same plane,
2. (Snell’s law) for any pair of media, the sin of i, the angle of incidence, is proportional to the sin of r, the angle of refraction.
   i. e. n= sin i/ sin r

Question 5

the refractive index

Answer 5

the refractive index of a medium is the ratio of the sine of the angle of incidence to the sine of the angle of refraction when light travels from a vacuum into that medium.
n = 1/sin c

Question 6

the critical angle

Answer 6

he angle of incidence for which the corresponding angle of refraction is 90˚

Question 7

total internal reflection

Answer 7

When light going from a denser to a rarer medium strikes the second medium with an angle of incidence greater than the critical angle, it does not enter the second medium. It is all reflected back in the denser medium.

Question 8

wave

Answer 8

a means of transferring energy through a medium, without any net movement of that medium.

Question 9

transverse wave

Answer 9

in a transverse wave, the movement of the particles is perpendicular to the movement of the wave.

Question 10

longitudinal wave

Answer 10

in a longitudinal wave, the movement of the particles is parallel to the movement of the waves

Question 11

diffraction

Answer 11

the ability of a wave to spread out after encountering an obstacle or after passing through a small gap

Question 12

interference

Answer 12

occurs when two waves meet. When this happens, the total displacement will be equal to the algebraic sum of the individual displacements.

Question 13

coherent waves

Answer 13

are two or more waves that have the same frequency and wavelength, and that are in phase or maintain a constant phase difference

Question 14

polarisation

Answer 14

the restriction of a wave to vibrations in one plane only

Question 15

standing wave

Answer 15

produced when two waves of the same frequency and amplitude meet, moving in opposite directions

Question 16

harmonics

Answer 16

multiples of the natural frequency of vibration of a body.

Question 17

resonance

Answer 17

the transfer of energy between two bodies of the same natural frequency

Question 18

intensity of sound

Answer 18

the intensity of sound at a point is defined as the rate at which energy is crossing a unit area perpendicular to the direction in which the sound is travelling

Question 19

threshold of hearing

Answer 19

the threshold of hearing is the lowest sound intensity to which an average human ear can respond. Its value is taken as 10^-12 Wm^-2

Question 20

the frequency limits of audibility

Answer 20

highest and lowest frequency sound waves that the average human can hear.

Question 21

doppler effect

Answer 21

the apparent change in the frequency of a wave due to the relative motion of the source of the wave or an observer is known as the doppler effect

Question 22

frequency of a wave

Answer 22

the frequency, f, is the number of cycles completed at any one point per second

Question 23

period of a wave

Answer 23

the period of a wave, T, is the time taken to undergo one complete cycle
f=1/T

Question 24

speed of a wave

Answer 24

the speed of a wave, c, is the speed of propagation through a medium.

Question 25

constructive interference

Answer 25

if the peak of one wave meets the peak of another

Question 26

destructive interference

Answer 26

if the peak of one wave meets the trough of another

Question 27

pitch corresponds with

Answer 27

frequency

Question 28

loudness corresponds with

Answer 28

amplitude

Question 29

quality corresponds with

Answer 29

the presence of harmonics

Question 30

Optical fibre

Answer 30

A very thin transparent rod (usually of glass) through which light can travel by total internal reflection

Question 31

Travelling mechanical wave

Answer 31

A disturbance carrying energy through a medium without any overall motion of that medium

Question 32

Travelling wave

Answer 32

Either mechanical or electromagnetic is a disturbance that travels out from the source producing it, transferring energy from one source to other places through which it passes

Question 33

Refraction of waves

Answer 33

The changing of direction of a wave when it enters a region where its speed changes

Question 34

Constructive interference

Answer 34

When waves from two sources meet and the amplitude of the resulting wave is greater than the amplitudes of each of the individual waves, the waves are said to undergo constructive interference

Question 35

Destructive interference

Answer 35

When waves from two sources meet and the amplitude of the resulting wave is less than the amplitude of each of the individual waves, the waves are undergoing destructive interference

Question 36

If λ is the wavelength of travelling waves causing the stationary wave then:

Answer 36

The distance between 2 consecutive nodes is λ/2.
The distance between 2 consecutive antinodes is λ/2.
The distance between an anti node and the next node is λ/4.

Question 37

Loudness

Answer 37

The loudness of a sound wave depends on the amplitude. The greater the amplitude the greater the sound

Question 38

Pitch

Answer 38

The pitch of the note depends on the frequency of the sound wave. The higher the frequency the higher the pitch

Question 39

Quality

Answer 39

The quality of a musical note depends on the number of overtones present in the note and the relative strengths of the different overtones

Question 40

Fundamental frequency of a string

Answer 40

A string vibrating with an anti node at its centre and a node at each end (and no other nodes or antinodes) is vibrating at its fundamental frequency

Question 41

Harmonics

Answer 41

Frequencies which are multiples of a certain frequency f are called harmonics. F is called the fundamental frequency or the first harmonic. If f is the first harmonic, 2f is the second

Question 42

The grating constant

Answer 42

The distance d between two adjacent slits on the grating is called the grating constant or grating spacing

Question 43

Dispersion

Answer 43

The separating out of the different wavelengths present in light