A-LevelPhysicsSuperposition9702/21 · May/June 2017 · Q47 Marks
State the conditions required for the formation of stationary waves.
- (a)State the conditions required for the formation of stationary waves.[2]
- (b)One end of a string is attached to a vibrator. The string is stretched by passing the other end over a pulley and attaching a load, as illustrated in Fig. 4.1. [Figure 4.1] The frequency of vibration of the vibrator is adjusted to 250 Hz and a transverse wave travels along the string with a speed of 12 m s⁻¹. The wave is reflected at the pulley and a stationary wave forms on the string. Fig. 4.2 shows the string between points A and B at time t = t₁. [Figure 4.2] At time t = t₁ the string has maximum displacement.
- (b)(i)Calculate the distance AB.[2]
- (b)(ii)On Fig. 4.2, sketch the position of the string between A and B at times 1. t = t₁ + 2.0 ms (label this line P), 2. t = t₁ + 5.0 ms (label this line Q).[3]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (May/June 2017). The mark or mark type is shown in brackets.
- [B1] (two) waves travelling (at same speed) in opposite directions overlap
- [B1] waves (are same type and) have same frequency/wavelength
- [C1] λ = 12 / 250 (= 0.048 m)
- [A1] distance = 1.5 × 0.048
- [A1] = 0.072 m
- [C1] T = 1/250
- [C1] = 0.004 (s) or 4 (ms)
- [A1] 1. curve drawn is mirror image of that in Fig. 4.2 and labelled P
- [A1] 2. horizontal line drawn between A and B and labelled Q
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