Superposition

Question 1

Principle of superposition

Answer 1

When waves meet, the actual displacement is the vector sum of the separate displacements of the individual waves, and each waves proceeds as though no other waves exists.

Question 2

Define coherent sources

Answer 2

Coherent sources are sources that have a constant phase difference.

Question 2

Define interference

Answer 2

Interference is the result of superposition of wavetrains from a finite number of coherent sources.

Question 2

Constructive interference

Answer 2

When two waves meet in phase at a point, they reinforce each other, and the resultant amplitude of the wave is a maximum.

Question 3

Destructive interference

Answer 3

When two waves meet in antiphase or exactly pi radians out of phase at a point, they cancel each other and the resultant amplitude of the wave is a minimum.

Question 3

Conditions for observable interference

Answer 3

1. sources must be coherent
2. amplitude of both waves, must be similar.
3. waves cannot be polarized in mutually perpendicular planets.

Question 3

Formation of stationary waves

Answer 3

Formed from the superposition of two progressive wavetrains of equal amplitude and frequency travelling with the same speed in opposite directions over the same space. There is no propagation of energy along the wave, and thus a stationary wave is characterized by nodes and antinodes occurring at fixed position.

Question 4

Define diffraction

Answer 4

Diffraction is the spreading of waves when they pass through an opening or around an obstacle.

Question 4

Formula for diffraction through single silt

Answer 4

equation indicating the position of first minimum.
sin θ = λ / b

θ = angle between first minimum and central maximum.
λ = wavelength
b = width of silt

Question 5

Rayleigh’s criterion

Answer 5

Rayleigh’s criterion says the images of two point sources can barely be distinguished from each other if the central maximum of one diffraction pattern falls on the first minimum of the other one.

Question 6

Formula to determine if image can be resolved

Answer 6

θ = λ / b
θ = angular separation of the two sources
λ = wavelength
b = width of slit
(rayleigh’s criterion for a single slit)

Question 7

Formula for double slit, find the separation of the fringes(x)
x = length between bright fringe to next bright fringe

Answer 7

λ = (a x) / D
λ = wavelength
a = distance between slits
D = distance between screen and double slit
(assuming D&raquo_space; a)

Question 8

Formula for double slit, find the nth maximum

Answer 8

d sin θ = nλ
d = separation between slits
λ = wavelength
n = order of maxima
θ = angle between nth order of maximum and central maximum