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. [1]

(ii) Calculate, in Hz, the frequency for this wave. [2]

(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. [2]

(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. [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:

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