We consider a thermodynamic system. If ΔU represents the increase in its internal energy and W the work done by the system, which of the following statements is true?

• ΔU = -W in an adiabatic process

• ΔU = W in an isothermal process

• ΔU = -W in an isothermal process

• ΔU = W in an adiabtic process

122.

When you make ice cubes, the entropy of water

• does not change

• increases

• decreases

• may either increase or decrease depeding on the process used

1 mole of an ideal gas at an initial temperature of T K does 6R joule of work adiabatically. If the ratio of specific heats of this gas at constant pressure and at constant volume is 5/3, then final temperature of the gas will be

• ( T - 4 ) K

• ( T + 4 ) K

• ( T - 2.4 ) K

• ( T + 2.4 ) K

In Carnot engine efficiency is 40% at hot reservoir temperature T.  For efficiency 50%,  what will be temperature of hot reservoir?

• $\frac{\mathrm{T}}{5}$

• $\frac{2 \mathrm{T}}{5}$

• 6 T

• $\frac{6\mathrm{T}}{5}$

During an adiabatic process, the pressure of a gas is found to be proportional to the cube of absolute temperature. The ratio $\frac{{\mathrm{C}}_{\mathrm{P}}}{{\mathrm{C}}_{\mathrm{V}}}$ for the gas is

• $\frac{4}{3}$

• 2

• $\frac{5}{3}$

• $\frac{3}{2}$

A diatomic gas (γ = 1.4) does 200 J of work when it is expanded isobarically. Find the heat given to the gas in the process

• 500 J

• 700 J

• 600 J

• 900 J

1 kg of water is converted into steam at the same temperature and at 1 atm (100 kPa). The density of water and steam are 1000 kgm^-3 and 0.6 kgm^-3 respectively. The latent heat of vaporisation of water is 2.25 x 10⁶ J kg^-1, What will be increase in energy?

• 3 × 10⁵ J

• 4 × 10⁶ J

• 2.08 × 10⁶ J

• None of these

A lead ball at 30°C is dropped from a height of 6.2 km. The ball is heated due to the air resistance and it completely melts just before reaching the ground. The molten substance falls slowly on the ground. If the specific heat of lead = 126 Jkg^-1 oC^-1 and melting point of lead= 130°C and suppose that any mechanical energy lost is used to heat the ball, then the latent heat of fusion of lead is

• 2.4 × 10⁴ J Kg^-1

• 3.6 × 10⁴ J Kg^-1

• 7.6 × 10² J kg^-1

• 4.94 × 10³ J kg^-1

The given p-V diagram shows gases during adiabatic process. Plots 1 and 2 should correspond respectively to

• He and O₂

• O₂ and He

• He and Ar

• O₂ and N₂

For an adiabatic expansion of a monoatomic perfect gas, the volume increases by 24%. What is the percentage decrease in pressure?

• 24%

• 40%

• 48%

• 71%