A-LevelPhysicsSuperposition9702/23 · May/June 2020 · Q410 Marks
Two progressive sound waves Y and Z meet at a fixed point P. The variation with time t of the displacement x of each wave at point P is shown in Fig. 4.1. [Figure 4.1]
- (a)(i)the same[1]
- (a)(ii)different.[1]
- (b)State and explain whether waves Y and Z are coherent.[1]
- (c)Determine the phase difference between the waves.[1]
- (d)The two waves superpose at P. Use Fig. 4.1 to determine the resultant displacement at time t = 0.75 ms.[1]
- (e)The intensity of wave Y at point P is I. Determine, in terms of I, the intensity of wave Z.[2]
- (f)The speed of wave Z is 330 m s⁻¹. Determine the wavelength of wave Z.[3]
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Mark scheme
Marking points from the official mark scheme (May/June 2020). The mark or mark type is shown in brackets.
- [B1] frequency or period
- [B1] amplitude
- [B1] constant phase difference so coherent
- [B1] 120°
- [B1] resultant displacement = 4.0 μm – 1.0 µm = 3.0 μm
- [C1] I ∝ A²
- [A1] intensity of Z = (2²/4²) I = 0.25 I
- [C1] v = λ/T or v = fλ and f = 1/T
- [C1] 330 = λ/3.0 × 10⁻³
- [A1] λ = 0.99 m
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