Download waves

Grade 12
Class Test: SHM, Diffraction, Interference, Reflection & Refraction
Marks: 30
1. In an experiment to measure the speed of sound, two coherent sources S1 and S2 produce sound waves
of frequency 1700 Hz. A sound detector is moved along a line AB, parallel to S1S2 as shown below.
When the detector is at P, such that S1P = S2P, maximum loudness of sound is detected. As the detector is
moved along AB, regions of minimum and maximum loudness are detected. Point X is the third position of
minimum loudness from P. The distance (S2 X − S1X) is 0.50 m.
(a) Determine the speed of the sound.
[3]
(b) At X, no sound is detected. The loudness of the sound produced by S1 alone is then reduced. State and
explain the effect of this change on the loudness of sound heard at X and at P.
[4]
2. Diagram 1 below shows a wave that approaches the boundary between medium 1 and medium 2.
AB and CD are two wavefronts of the wave.
Diagram 2 shows the situation a time later when point C of the wavefront CD has just reached the
boundary. The speed of the wave in medium 1 is v1 and the speed in medium 2 is v2. v1 is greater than v2
1
(a) Redraw Diagram 2 on your answer sheet. On diagram 2 on your answer sheet:
(i) draw ray C continuing in medium 2
[1]
(ii) draw the wavefront AB
[1]
(iii) label the distance travelled by point B with the letter ‘s’.
[1]
(b) In medium 1 the wave has a wavelength of 4.0 cm and travels at a speed of 8.0 cm s−1.
Determine the frequency of the wave in medium 2.
[2]
(c) For the ray C, the angle of incidence is 60º and the angle of refraction is 35º. Calculate the speed of
the wave in medium 2.
[2]
3. The graph shows the variation with time of the displacement of an object undergoing simple harmonic
motion.
(a) State the amplitude of the oscillation.
[1]
(b) Calculate the frequency of the oscillation.
[2]
(c) Determine the maximum speed of the object.
[2]
(d) Determine the acceleration of the object at 140 ms.
[2]
2
4. Light of wavelength 633 nm is incident on a narrow slit. The angle between the first diffraction minimum
on one side of the central maximum and the first minimum on the other side is 1.20º.
(a) Calculate the width of the slit.
[3]
(b) The frequency of light incident on the slit is now increased. State and explain any change in the
intensity pattern produced.
[2]
5. The figure below shows a triangular prism of glass in air. An incident ray enters the glass as shown in the
diagram and undergoes total internal reflection at the glass-air interface. If q1 is 45°, what can you say
about the refractive index n of the glass?
[4]
3