One end of a string is attached to an oscillator and the other is fixed to a wall. When the frequency of the oscillator is 360 Hz the standing wave shown is formed on the string.
Point X (not shown) is a point on the string at a distance of 10 cm from the oscillator.
(i) State the number of all other points on the string that have the same amplitude and phase as X. 
(ii )The frequency of the oscillator is reduced to 120 Hz. On the diagram, draw the standing wave that will be formed on the string. 
i 3 «points»
ii first harmonic mode drawn
The sound wave in air in (c) enters a pipe that is open at both ends. The diagram shows the displacement, at a particular time T, of the standing wave that is set up in the pipe.
A particular air molecule has its equilibrium position at the point labelled M. On the diagram, at time T,
draw an arrow to indicate the acceleration of this molecule. 
label with the letter C a point in the pipe that is at the centre of a compression. 
i horizontal arrow «at M» pointing left
any point labelled C on the vertical line shown below