Question 22M.2.HL.TZ1.3a
| Date | May 2022 | Marks available | [Maximum mark: 3] | Reference code | 22M.2.HL.TZ1.3a |
| Level | HL | Paper | 2 | Time zone | TZ1 |
| Command term | Explain | Question number | a | Adapted from | N/A |
Two loudspeakers A and B are initially equidistant from a microphone M. The frequency and intensity emitted by A and B are the same. A and B emit sound in phase. A is fixed in position.
B is moved slowly away from M along the line MP. The graph shows the variation with distance travelled by B of the received intensity at M.
Explain why the received intensity varies between maximum and minimum values.
[3]
movement of B means that path distance is different « between BM and AM »
OR
movement of B creates a path difference «between BM and AM» ✓
interference
OR
superposition «of waves» ✓
maximum when waves arrive in phase / path difference = n x lambda
OR
minimum when waves arrive «180° or » out of phase / path difference = (n+½) x lambda ✓
This was an "explain" questions, so examiners were looking for a clear discussion of the movement of speaker B creating a changing path difference between B and the microphone and A and the microphone. This path difference would lead to interference, and the examiners were looking for a connection between specific phase differences or path differences for maxima or minima. Some candidates were able to discuss basic concepts of interference (e.g. "there is constructive and destructive interference"), but failed to make clear connections between the physical situation and the given graph. A very common mistake candidates made was to think the question was about intensity and to therefore describe the decrease in peak height of the maxima on the graph. Another common mistake was to approach this as a Doppler question and to attempt to answer it based on the frequency difference of B.
