Question
(a) State what is meant by the diffraction of a wave. [2]
(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 [3]
(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. [2]
[Total: 7]
Answer/Explanation
Ans
(a) wave incident on/passes by or through an aperture/edge
wave spreads (into geometrical shadow)
(b) nλ = d sinθ
substitution of θ = 90° or sinθ = 1
4 × 500 × 10–9 = d × sin90°
line spacing = 2.0 × 10–6m A1 [3]
(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:…………………………………………………………………………………………….
……………………………………………………………………………………………………………….[3]
(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.
Show your working.
number =………………………………………..[3]
(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 \(S_2\).
………………………………………………………………………………………………………..
…………………………………………………………………………………..[1]
Answer/Explanation
Ans: