set 6 MCQ Questions & Answers Detailed Explanation

Answer: (b)

The faster the vibration of source, the higher is the frequency and the higher is the pitch.

Answer: (a)

Some bodies like wood, rubber etc. have negative value of coefficient of thermal expansion, hence they contract on heating.

Hence 1 is true. 2 is also true.

Answer: (a)

A shock wave is a type of propagating disturbance. Like an ordinary wave, it carries energy and can propagate through a medium (solid, liquid, gas or plasma) or in some cases in the absence of a material medium. Across a shock wave there is always an extremely rapid rise in pressure, temperature and density of the flow.

Ultrasound is sound with a frequency greater than the upper limit of human hearing (greater than 20 kHz).

Answer: (b)

1. The process of a liquid changing into its vapour below its boiling point is called evaporation. In this process remaining water after evaporation loses heat and gets cooled.
2. If a gas is compressed, work is done on it which results in heating of the system or an increase in temperature.
3. On shaking a liquid in a vessel, the kinetic energy of liquid molecules increases and hence, the temperature of the system increases.

4. In adiabatic process ΔQ = 0

   From the first law of thermodynamics,

   ΔQ = ΔU + ΔW

   We have ΔU + ΔW = 0

   If the gas expands adiabatically (DW→positive), DU will be negative, so internal energy and hence, the temperature of the system will decrease. Thus, the gas is cooled.

Thus option (b) is correct.

Answer: (c)

Answer: (b)