A-LevelPhysicsWaves9702/42 · Oct/Nov 2019 · Q64 Marks
The variation with time of the displacement of an amplitude-modulated (AM) wave is shown in Fig. 6.1. [Figure 6.1] The sinusoidal information signal has frequency 10 kHz.
- (a)Determine the frequency of the carrier wave. frequency = ..................................................... Hz [1][1]
- (b)On the axes of Fig. 6.2, sketch the frequency spectrum of the modulated wave. [Figure 6.2][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 (Oct/Nov 2019). The mark or mark type is shown in brackets.
- [A1] period = 5.0 µs, so frequency = 2.0 × 10⁵ Hz
- [B1] sketch: three equally spaced vertical lines sitting on f-axis
- [B1] two outer vertical lines of equal length and central line longer
- [B1] three vertical lines (and no others) shown at frequencies 190 kHz, 200 kHz and 210 kHz
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