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 Physics Paper 2, MAy/June. 2009
 Questions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Main

Weakness/Remedies
Strength

Question 13

(a) State two differences between a sound wave and a radio wave.

(b) Explain why a vibrating tuning fork sounds louder when its stem is pressed against a table top than when held in air.

(c)State two conditions necessary for the:

• production of stationary wave in a medium;
• formation of interference wave patterns;
• occurrence of total internal reflection of a wave.
(d) A ray of light is incident on one face of an equilateral glass prism.
• Draw a ray diagram to show the path of the ray through the prism.
• Calculate the refractive index of the glass if the angle of minimum deviation is 41o.
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Observation

This question was very popular among the candidates and the overall performance was well above average except in part (c)(ii).

The expected answers were as follows:

(a) Differences between a sound wave and a radiowave

 Sound wave Radio wave is a mechanical wave is an electromagnetic wave is longitudinal is transverse has speed less than speed of light. has speed equal to that of light requires a material medium for propagation/cannot travel through vacuum. does not require a material medium for propagation/can travel through vacuum.

(i)
(b) The vibrating tuning fork forces the table top to vibrate.  The table top has a much larger area and is therefore in contact with a larger volume of air undergoing vibration.  Hence, sound heard is amplified.

(c)       Conditions necessary for:

(i)   production of stationary wave
-    Two waves must be traveling in opposite directions.
-     Incident and reflected waves must have the same frequency/wavelength.
-     Incident and reflected waves must have equal amplitude.
-     There must be superimposition.
-     There must be a barrier

(ii)    formation of interference wave pattern
- Two sources must be involved.
- The two sources must be coherent/have a constant phase difference as well as the same frequency and amplitude.
- The waves that are interfering must have the same amplitude
-  The distance between the sources must be of the order of the wavelengths of the waves.

(iii)   total internal reflection
-  The wave must be traveling from a denser medium to a less dense medium
-  The angle of incidence of the wave in the denser medium must be greater than the critical angle for the medium.

(d)(i)  Diagram

Correct diagram

(ii)                  Sin (A + dm)
n  = 2
Sin (A/2)

Sin (60 + 41)
=                 2
Sin   (60/2)

=   1.54