# CIE AS & A Level Physics : 8.2 Diffraction- Exam style question – Paper 2

### Question

(a) State what is meant by the diffraction of a wave.                                                                                  
(b) Laser light of wavelength 500 nm is incident normally on a diffraction grating. The resulting
diffraction pattern has diffraction maxima up to and including the fourth-order maximum.
Calculate, for the diffraction grating, the minimum possible line spacing.

line spacing = ……………………………………………… m 
(c) The light in (b) is now replaced with red light. State and explain whether this is likely to result
in the formation of a fifth-order diffraction maximum.                                                                       
[Total: 7]

Ans

(a) wave incident on/passes by or through an aperture/edge
(b) nλ = d sinθ
substitution of θ = 90° or sinθ = 1
4 × 500 × 10–9 = d × sin90°
line spacing = 2.0 × 10–6m A1 
(c) wavelength of red light is longer (than 500 nm) M1
(each order/fourth order is now at a greater angle so) the fifth-order maximum
cannot be formed/not formed

### Question

(a) State what is meant by diffraction and by interference.
diffraction:……………………………………………………………………………………………….

……………………………………………………………………………………………………………….
interference:…………………………………………………………………………………………….

……………………………………………………………………………………………………………….
(b) Light from a source $$S_1$$ is incident on a diffraction grating, as illustrated in Fig. 6.1. The light has a single frequency of $$7.06 \times 10^{14}$$ Hz. The diffraction grating has 650 lines per millimetre.
Calculate the number of orders of diffracted light produced by the grating. Do not include the zero order.
(c) A second source $$S_2$$ is used in place of $$S_1$$,. The light from $$S_2$$ has a single frequency lower than that of the light from $$S_1$$.
State and explain whether more orders are seen with the light from $$S_2$$. 