2011 Question 8 (a)
Destructive interference can occur when waves from coherent sources meet.
(i) Explain the underlined term.
(ii) Give two other conditions necessary for total destructive interference to occur.
(iii)The diagram shows a standing wave in a pipe closed at one end.
The length of the pipe is 90 cm.
Name the points on the wave labelled P and Q.
(iv) Calculate the frequency of the standing wave.
(v) What is the fundamental frequency of the pipe?
(vi) The clarinet is a wind instrument based on a pipe that is closed at one
end. What type of harmonics is produced by a clarinet?
2011 Question 8 (b)
An audio speaker at a concert emits sound uniformly in all directions at a rate of 100 W.
Calculate the sound intensity experienced by a listener at a distance of 8 m from the speaker.
The listener moves back from the speaker to protect her hearing.
At what distance from the speaker is the sound intensity level reduced by 3 dB?
(speed of sound in air = 340 m s–1)
2011 Question 12 (b)
(i) State the laws of refraction of light.
(ii) A lamp is located centrally at the bottom of a large swimming pool, 1.8 m deep.
Draw a ray diagram to show where the lamp appears to be, as seen by an observer standing at
the edge of the pool.
(iii)At night, when the lamp is switched on, a disc of light is seen at the surface of the swimming
pool. Explain why the area of water surrounding the disc of light appears dark.
(iv) Calculate the area of the illuminated disc of water.
(refractive index of water = 1.33)
