A device containing a microwave emitter and receiver is placed in front of a large metal sheet in a vacuum as shown in [Figure 4.1]. The line XY is perpendicular to the metal sheet. The device emits microwaves of frequency 6.3 GHz.

1. (a)When the device is at position P, a stationary wave is formed between the device and the sheet. Explain how the stationary wave, including the nodes and the antinodes, is formed.[4]
2. (b)(i)Calculate the wavelength of the microwaves. wavelength = ................................................................m [2][2]
3. (b)(ii)At point P the receiver detects a maximum amplitude of the stationary wave. The device is moved slowly from point P along the line XY and the receiver detects a series of minimum and maximum amplitudes. The first time a minimum amplitude is detected by the receiver is when the device is at point Q. Determine the distance between P and Q. distance = ................................................................m [1][1]
4. (b)(iii)The intensity of the microwaves emitted by the device is increased. The frequency of the microwaves is unchanged. The device is moved slowly along the line XY from point Q until the next maximum amplitude is detected at point R. State and explain whether the distance QR is greater than, less than or the same as distance PQ.[1]

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.