(b) This diagram shows an experiment to measure the speed of a sound in a string. The frequency of the vibrator is adjusted until the stationary wave shown is formed.

(i) On a copy of the diagram, mark a node (label it N) and an antinode (label it A).

(b) This diagram shows an experiment to measure the speed of a sound in a string. The frequency of the vibrator is adjusted until the stationary wave shown is formed.

(ii) The frequency of the vibrator is 120Hz. Calculate the speed at which a progressive wave would travel along the string.

This diagram shows a stationary wave, of frequency $400\mathrm{Hz}$, produced by a loudspeaker in a closed tube.

(a) Describe the movement of the air particles at:

(i) $\left(\mathrm{A}\right)$

This diagram shows a stationary wave, of frequency $400\mathrm{Hz}$, produced by a loudspeaker in a closed tube.

(a) Describe the movement of the air particles at:

(ii) $\left(\mathrm{B}\right)$

This diagram shows a stationary wave, of frequency $400\mathrm{Hz}$, produced by a loudspeaker in a closed tube.

(b) The length the tube is $63.8\mathrm{cm}$.

Calculate the speed of the sound.

(a) Explain what is meant by:

(i) A coherent source of waves.

(a) Explain what is meant by:

(ii) Phase difference.

(b) A student, experimenting with microwaves, sets up the arrangement shown in this diagram.

With the metal plate at position $\mathrm{A}$ there is a very small signal. He slowly moves the plate back, leaving the receiver in the same position. As he does so, he finds that the intensity initially rises until it becomes a maximum, then falls back to a minimum. This cycle repeats a total of five times until the plate reaches position $\mathrm{B}$, where once again there is a minimum.

(i) Explain why a series of maxima and minima are heard.