Question
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. [1]
(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. [1]
Answer/Explanation
Ans
i 3 «points»
ii first harmonic mode drawn
Question
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. [1]
label with the letter C a point in the pipe that is at the centre of a compression. [1]
Answer/Explanation
Ans
i horizontal arrow «at M» pointing left
ii
any point labelled C on the vertical line shown below
