Question 20N.2.SL.TZ0.4
| Date | November 2020 | Marks available | [Maximum mark: 8] | Reference code | 20N.2.SL.TZ0.4 |
| Level | SL | Paper | 2 | Time zone | TZ0 |
| Command term | Deduce, Estimate, Predict | Question number | 4 | Adapted from | N/A |
Two loudspeakers, A and B, are driven in phase and with the same amplitude at a frequency of . Point P is located from A and from B. The speed of sound is .
Deduce that a minimum intensity of sound is heard at P.
[4]
wavelength✓
path difference ✓
OR «half-wavelengths» ✓
waves meet in antiphase «at P»
OR
destructive interference/superposition «at P» ✓
Allow approach where path length is calculated in terms of number of wavelengths; along path A () and
path B () for MP2, hence path difference wavelengths for MP3
A microphone moves along the line from P to Q. PQ is normal to the line midway between the loudspeakers.
The intensity of sound is detected by the microphone. Predict the variation of detected intensity as the microphone moves from P to Q.
[2]
«equally spaced» maxima and minima ✓
a maximum at Q ✓
four «additional» maxima «between P and Q» ✓
When both loudspeakers are operating, the intensity of sound recorded at Q is . Loudspeaker B is now disconnected. Loudspeaker A continues to emit sound with unchanged amplitude and frequency. The intensity of sound recorded at Q changes to .
Estimate .
[2]
the amplitude of sound at Q is halved ✓
«intensity is proportional to amplitude squared hence» ✓