| Date | May 2012 | Marks available | 1 | Reference code | 12M.3.SL.TZ2.2 |
| Level | Standard level | Paper | Paper 3 | Time zone | Time zone 2 |
| Command term | State | Question number | 2 | Adapted from | N/A |
Question
This question is about standing (stationary) waves.
State one way in which a standing wave differs from a travelling (progressive) wave.
A loudspeaker connected to a signal generator is placed in front of the open end of a tube.
The frequency of the sound is slowly increased from zero. At a frequency of 92.0 Hz the first large increase in the intensity of the sound is heard.
(i) On the diagram above, draw a representation of the wave in the tube for the frequency of 92.0 Hz.
(ii) The length of the tube is 0.910 m. Determine the speed of sound in the tube.
The frequency of sound is continuously increased above 92.0Hz.
Calculate the frequency at which the next large increase in the intensity of the sound is heard.
Markscheme
standing waves do not transfer energy;
standing waves do not have a constant amplitude;
points on a standing wave between consecutive nodes have a constant phase;
standing waves have permanent nodes/antinodes;
(i) correct diagram as shown; (dotted line not essential for the mark)
(ii) wavelength of sound is (4×0.910)=3.64m;
speed of sound 3.64×92=335ms-1;
the next harmonic has wavelength \(\frac{{4 \times 0.910}}{3} = \frac{{3.64}}{3}{\rm{m}}\);
and so frequency 3×92=276Hz ;
Examiners report
