Chapter 12 Superposition

Question 1

Principle of superposition

Answer 1

When waves meet the actual displacement is the vector sum of separate displacements of individual waves, and each wave proceeds as don’t know other waves exist

Question 2

Interference

Answer 2

A result of superposition of wave trains from a finite number of coherent sources

Question 3

Coherent sources

Answer 3

Sources that have a constant phase difference

Question 4

Constructive interference

Answer 4

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

Question 5

Destructive interference

Answer 5

When two waves meet in antiphase, they cancel each other out and the resultant amplitude of the wave is a minimum.

Question 6

Conditions for observable interference

Answer 6

Sources must be coherent

Amplitude of both waves must be similar

Waves cannot be polarized in mutually perpendicular planes

Question 7

Diffraction

Answer 7

Spreading of waves when they pass through an opening or around an obstacle

Question 8

Equation indicating position of first minimum

Answer 8

sinθ = λ/b
θ: angle subtended by first minimum and central maximum
λ: wavelength of incident light
b: width of slit

Question 9

Rayleigh’s criterion

Answer 9

Images of two point sources can just barely be distinguished from each other if the central maximum of one diffraction pattern falls on the first minimum of the other one

θ = λ/b

Question 10

Double slit
Separation of fringes formula

Answer 10

λ = ax/D
λ: wavelength of incident light
a: distance between slits
D: distance between screen and double slit
x: fringe separation

Question 11

Diffraction grating for nth order maximum

Answer 11

d sin θn = nλ
d: slit separation
θn: angle btw nth max and centre
λ: wavelength of incident light