(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 41\(^o\).
Explanation
(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. |
(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) \(\frac{ Sin (A + dm)}{2}\)
n =
Sin (A/2)
Sin (60 + 41)/2
Sin (60/2)
= 1.54