A-LevelPhysicsSuperposition9702/22 · Oct/Nov 2018 · Q55 Marks
Red light of wavelength 640 nm is incident normally on a diffraction grating having a line spacing of 1.7 × 10⁻⁶m, as shown in Fig. 5.1. [Figure 5.1] The second order diffraction maximum of the light is at an angle θ to the direction of the incident light.
- (a)Show that angle θ is 49°.[3]
- (b)Determine a different wavelength of visible light that will also produce a diffraction maximum at an angle of 49°. wavelength = m[2]
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Mark scheme
Marking points from the official mark scheme (Oct/Nov 2018). The mark or mark type is shown in brackets.
- [C1] nλ = d sinθ
- [C1] λ = 640 × 10⁻⁹ (m)
- [A1] 2 × 640 × 10⁻⁹ = 1.7 × 10⁻⁶ × sinθ
- [A1] so θ = 49(°)
- [C1] 2 × 640 × 10⁻⁹ = 3 × λ
- or
- [C1] 1.7 x 10⁻⁶ x sin 49° = 3 × λ
- [A1] λ = 4.3 × 10⁻⁷ m
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