# IBDP Physics Topic 4. Waves – Travelling waves- IB Style Question Bank HL Paper 2

### Question

The solid line in the graph shows the variation with distance x of the displacement y of a travelling wave at t = 0. The dotted line shows the wave 0.20 ms later. The period of the wave is longer than 0.20 ms. (a)     (i) Calculate, in m s–1, the speed for this wave. 

(ii) Calculate, in Hz, the frequency for this wave. 

(b) The graph also shows the displacement of two particles, P and Q, in the medium at t = 0. State and explain which particle has the larger magnitude of acceleration at t = 0. 

(c) 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. Ans:

a i v= « $$\frac{0.05}{0.20\times 10^{-3}}$$ = » 250 «ms-1»

a ii λ = 0.30 «m » f = « $$\frac{250}{0.30}$$ = » 830 «Hz»

b Q  acceleration is proportional to displacement «and Q has larger displacement»

c i 3 «points»

c ii first harmonic mode drawn 