When the device is at position P, a stationary wave is set up between the device and the sheet. Explain how this stationary wave is formed, including the nodes and the antinodes.
Calculate the wavelength for the microwaves.
At point $P$ the receiver records a maximum amplitude for the stationary wave. The device is then moved slowly from point $P$ along line $XY$ and the receiver records a sequence of minimum and maximum amplitudes. The first time the receiver detects a minimum amplitude is when the device is at point $Q$. Determine the distance between $P$ and $Q$.
The intensity of the microwaves emitted by the device is increased. The frequency of the microwaves stays the same. The device is moved slowly along 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.