21.

1 g of steam is sent into 1 g of ice. At thermal equilibrium, the resultant temperature of mixture is

• 270^oC

• 230^oC

• 100^oC

• 120^oC

The molar specific heats of an ideal gas at constant pressure and volume are denoted by C_P and  C_V respectively.  If  $\mathrm{\gamma } = \frac{{\mathrm{C}}_{\mathrm{P}}}{{\mathrm{C}}_{\mathrm{V}}}$ and R is then C_V universal gas constant, then C_V is equal to

• $\frac{\mathrm{\gamma } - 1}{\mathrm{R}}$

• γR

• $\frac{1 + \mathrm{\gamma }}{1 - \mathrm{\gamma }}$

• $\frac{\mathrm{R}}{\left(\mathrm{\gamma } - 1\right)}$

Assertion:  Water kept in an open vessel will quickly evaporate on the surface of the moon. 

Reason:  The temperature at the surface of the moon is much higher than the boiling point of water.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

Assertion: A undamped spring-mass system is simplest free vibration system. 

Reason: It has three degrees of freedom.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

Which of the following is the best method to reduce eddy currents?

• Laminating core

• Using thick wires

• Reducing hysteresis loss

• None of these

In an oscillating system, a restoring force is a must. In an L-C circuit, restoring force is provide by

• capacitor

• inductance

• resistance

• both (a) and (b)

Given that the mobility of electrons in Ge is 0.4 m² V^-1  S^-1 and electronic charge is 1.6 × 10^-19 C. The number of donor atom ( per m³ ) semiconductor of conductivity 500 mho/m is

• 8 × 10²¹

• 8 × 10¹⁵

• 5 × 10²¹

• 8 × 10¹⁶

Two solenoids of equal number of turns having their length and the radii in the same ratio 1:2. The ratio of their self-inductance will be

• 1:2

• 2:1

• 1:1

• 1:4

A circuit consisting of five resistors each of resistance R, forming a Wheatstone bridge. What is the equivalent resistance of the circuit?

• 2R

• R

• 2R/3

• R/2

An engine has an efficiency of 1/6. When the temperature of sink is reduced by 62^oC, its efficiency is doubled. The temperature of source will be

• 37^o C

• 62^o C

• 99^o C

• 124^o C