Question 22N.2.HL.TZ0.3
| Date | November 2022 | Marks available | [Maximum mark: 11] | Reference code | 22N.2.HL.TZ0.3 |
| Level | HL | Paper | 2 | Time zone | TZ0 |
| Command term | Calculate, Describe, Determine, Discuss, Draw, Outline | Question number | 3 | Adapted from | N/A |
A string of length 0.80 m is fixed at both ends. The diagram shows a standing wave formed on the string. P and Q are two particles on the string.
The variation with time t of the displacement of particle P is shown.
It is suggested that the speed c of waves in the string is related to the tension force T in the string according to the equation T = ac2, where a is a constant.
The standing wave on the string creates a travelling sound wave in the surrounding air.
The sound wave is incident on a surface of water. The wave makes an angle of 30° with the normal to the surface.
Draw, on the axes, a graph to show the variation with t of the displacement of particle Q.
[2]
oscillation in antiphase ✓
smaller amplitude than P ✓
Although there were good answers which scored full marks, there were a significant number of wrong answers where the amplitude was the same or not consistent throughout, or the wave drawn was not in antiphase of the original sketch.
Calculate the speed of waves on the string.
[2]
wavelength «m» ✓
speed «m s−1» ✓
Allow ECF from incorrect wavelength.
This was well answered, particularly MP1 to determine the wavelength, although several candidates misinterpreted the unit of time and obtained a very small value for the velocity of the wave.
Determine the fundamental SI unit for a.
[2]
kg m s−2 OR m2 s−2 seen ✓
kg m−1 ✓
Award [2] for a BCA.
Students seem to be well prepared for this sort of question, as it was high-scoring.
The tension force on the string is doubled. Describe the effect, if any, of this change on the frequency of the standing wave.
[2]
speed increases hence frequency increases ✓
by factor ✓
This question was answered well, although the numerical aspect was often missing. It is worth highlighting that if there is a term like 'doubled' in the question, it makes sense to expect a numerical answer.
Outline one difference between a standing wave and a travelling wave.
[1]
travelling waves transfer energy OR standing waves don’t ✓
amplitude of oscillation varies along a standing wave OR is constant along a travelling wave ✓
standing waves have nodes / antinodes OR travelling waves don’t ✓
points in an internodal region have same phase in standing waves OR different phase in travelling waves ✓
This question was answered well. Students showed to be familiar with the differences between standing and travelling waves.
The speed of sound in air is 340 m s−1 and in water it is 1500 m s−1.
Discuss whether the sound wave can enter the water.
[2]
ALTERNATIVE 1
critical angle «from » ✓
the angle of incidence is greater than hence the sound can’t enter water ✓
ALTERNATIVE 2
✓
sine value greater than one hence the sound can’t enter water ✓
Conclusion must be justified, award [0] for BCA.
Surprisingly well answered as it was sound from air to water, rather than light from air to glass. A mixture of approaches but probably the most common was to calculate a sine value of over 1. Some went about calculating the critical angle but nowhere near as many.