| Date | May 2012 | Marks available | 4 | Reference code | 12M.2.HL.TZ1.4 |
| Level | Higher level | Paper | Paper 2 | Time zone | Time zone 1 |
| Command term | Question number | 4 | Adapted from | N/A |
Question
This question is about the Doppler effect.
A source emits sound of frequency 100Hz. The speed of sound in air is 330ms–1.
Calculate the frequency measured by an observer when
(i) the observer is stationary and the source is moving towards the observer at 120 ms–1.
(ii) the source is stationary and the observer is moving towards the source at 120 ms–1.
When both source and observer are stationary the wavelength is λ0 and the wavespeed is v0.
In the table below, compare the values of measured wavelength and measured wavespeed, as measured by the observer, with respect to λ0 and v0. One of the values is given for you.
Markscheme
(i) \(f' = \left( {f\left[ {\frac{v}{{v - {u_s}}}} \right] = } \right)100 \times \left[ {\frac{{330}}{{330 - 120}}} \right]\);
f'=157Hz;
(ii) \(f' = \left( {f\left[ {\frac{{v + {u_0}}}{{{v_s}}}} \right] = } \right)100 \times \left[ {\frac{{330 + 120}}{{330}}} \right]\);
f'=136Hz;
