A body initially at 80°C cools to 64°C in 5 min and to 52°C in 10 min. The temperature of the surrounding is

• 26^oC

• 16^oC

• 36^oC

• 40^oC

Two chambers containing m₁ g and m₂ g of a gas at pressures P₁ and P₂ respectively are put in communication with each other, temperature remaining constant. The common pressure reached will be

• $\frac{{\mathrm{P}}_1{\mathrm{P}}_2 \left( {\mathrm{m}}_1 + {\mathrm{m}}_2 \right)}{\left( {\mathrm{P}}_2 {\mathrm{m}}_1 + {\mathrm{P}}_1 {\mathrm{m}}_2 \right)}$

• $\frac{{\mathrm{P}}_1 {\mathrm{P}}_2 {\mathrm{m}}_1}{{\mathrm{P}}_2{\mathrm{m}}_1 + {\mathrm{P}}_1 {\mathrm{m}}_2}$

• $\frac{{\mathrm{m}}_1 {\mathrm{m}}_2 \left({\mathrm{P}}_1 + {\mathrm{P}}_2\right)}{{\mathrm{P}}_2 {\mathrm{m}}_1 + {\mathrm{P}}_1{\mathrm{m}}_2}$

• $\frac{{\mathrm{m}}_1 {\mathrm{m}}_2{\mathrm{P}}_2}{{\mathrm{P}}_2 {\mathrm{m}}_1 + {\mathrm{P}}_1{\mathrm{m}}_2 }$

Assertion: A piece of ice, with a stone frozen inside it, floats on water in a beaker. When the ice melts, the level of water in the beaker decreases.

Reason:  Density ofstone is more than that 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.

The temperature of a body is increased from $-$73^o C to 327^o C. Then the ratio of emissive power is

• 1/9

• 1/27

• 27

• 81

When a current is passed in a conductor, 5°C rise in temperature is observed. If the strength of current is made thrice, rise in temperature will be

• 5 ^oC

• 20 ^oC

• 45 ^oC

• 15 ^oC

If 10goficeis added to 40 g of water at 15°C, then the temperature of the mixture is(specific heat of water = 4.2 x 10³ J kg^-1K^-1, Latent heat of fusion of ice = 3.36 x 10⁵ J kg^-1 )

• 15 ^oC

• 12 ^oC

• 10 ^oC

• 0 ^oC

137.

A copper ball 2 cm in radius is heated in a furnace to 327 °C. If its emissivity is 0.3, at what rate does it radiate energy?

• 1.72 W

• 2.73 W

• 11.0 W

• 2.15 W

• higher than 0°C

• higher than 0 K

• higher than that of its surroundings

• high enough for it to glow

Assertion:  A hollow metallic closed container with small opening maintained at a high temperature can act as a source of black body radiation.

Reason:  All metals act as black body radiator.

• 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.

70 calories of heat are required to raise the temperature of 2 moles of an ideal gas at constant pressure from 30°C to 35°C.  The amount of heat required to raise the temperature of the same sample of the gas increases with through the same range at constant volume is (Gas constant= 1·99 cal/K-mole)

• 30 cal

• 50 cal

• 70 cal

• 90 cal