# First Year Physics Heat and Thermodynamics Does entropy of a system increases or decreases due to friction?

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##### Does entropy of a system increases or decreases due to friction?

Show that ratio of the root mean square speeds of molecules of two different gases at a certain temperature is equal to the square root of the inverse ratio of their masses.

Which one of the following process is irreversible?(a) Slow compressions of an elastic spring.(b) Slow evaporation of a substance in an isolated vessel.(c) Slow compression of a gas.(d) A chemical explosion.

EXAMPLE 11.4The turbine in a steam power plant takes steam from a boiler at 427{ }^{\circ} \mathrm{C} and exhausts into a low temperature reservoir at 77^{\circ} \mathrm{C} . What is the maximum possible efficiency.

A carnot engine utilises an ideal gas. The source temperature is 227^{\circ} \mathrm{C} and the sink temperature is 127^{\circ} \mathrm{C} . Find the efficiency of the engine. Also find the heat input from the source and heat rejected to the sink when 10000 \mathrm{~J} of work is done.

A heat engine performs 100 \mathrm{~J} of work and at the same time rejects 400 \mathrm{~J} of heat energy to the cold reservoirs. What is the efficiency of the engine?

Is it possible to convert internal energy into mechanical energy? Explain with an example.

A sample of gas is compressed to one half of its initial volume at constant pressure of 1.25 \times 10^{5} \mathrm{Nm}^{-2} . During the compression 100 \mathrm{~J} of work is done on the gas. Determine the final volume of the gas.

What happens to the temperature of the room when a air conditioner is left running on a table in the middle of the room?

Give an example of a process in which no heat is transferred to or from the system but the temperature of the system changes.

EXAMPLE 11.5Calculate the entropy change when 1.0 \mathrm{~kg} ice at 0^{\circ} \mathrm{C} melts into water at 0^{\circ} \mathrm{C} . Latent heat of fusion of ice L_{f}=3.36 \times 10^{5} \mathrm{~J} \mathrm{~kg}^{-1} .

A thermodynamic system undergoes a process in which its internal energy decreases by 300 \mathrm{J} . If at the same time 120 \mathrm{~J} of work is done on the system find the heat lost by the system.

Which one of the following process is irreversible?(a) Slow compressions of an elastic spring.(b) Slow evaporation of a substance in an isolated vessel.(c) Slow compression of a gas.(d) A chemical explosion.

Specific heat of a gas at constant pressure is greater than specific heat at constant volume. Why?

A Carnot engine whose low temperature reservoir is at 7^{\circ} \mathrm{C} has an efficiency of 50 \% . It is desired to increase the efficiency to 70 \% . By how many degrees the temperature of the source be increased?

Give an example of a natural process that involves an increases in entropy.

A reversible engine works between two temperatures whose difference is 100^{\circ} \mathrm{C} . If it absorbs 746J of heat from the source and rejects 546 \mathrm{~J} to the sink calculate the temperature of the source and the sink.

A thermos flask containing milk as a system is shaken rapidly. Does the temperature of milk rise?

A reversible engine works between two temperatures whose difference is 100^{\circ} \mathrm{C} . If it absorbs 746J of heat from the source and rejects 546 \mathrm{~J} to the sink calculate the temperature of the source and the sink.

Why is average velocity of the molecules in a gas zero but the average of the square of velocities is not zero?

EXAMPLE 11.2Find the average speed of oxygen molecule in the air at S.T.P.

A heat engine performs 100 \mathrm{~J} of work and at the same time rejects 400 \mathrm{~J} of heat energy to the cold reservoirs. What is the efficiency of the engine?

A mechanical engineer develops an engine working between 327^{\circ} \mathrm{C} and 27^{\circ} \mathrm{C} and claim to have an efficiency of 52 \% . Does he claim correctly? Explain.

Estimate the average speed of nitrogen molecules in air under standard conditions of pressure and temperature.

What happens to the temperature of the room when a air conditioner is left running on a table in the middle of the room?

Variation in volume by pressure is given in Fig. 11.13. A gas is taken along the paths A B C D A A B C A and A to A . What will be the change in internal energy?(a)(b)(c)

A system undergoes from state P_{1} V_{1} to state P_{2} V_{2} as shown in figure 11.12 . What will be the change in internal energy?

A steam engine has boiler that operates at 450 \mathrm{~K} . The heat changes water to steam which derives the piston. The exhaust temperature of the outside air is about 300 \mathrm{~K} . What is maximum efficiency of this steam engine?

336 \mathrm{~J} of energy is required to melt 1 \mathrm{~g} of ice at 0^{\circ} \mathrm{C} what is the change in entropy of 30 \mathrm{~g} of water at 0^{\circ} \mathrm{C} as it changed to ice at 0^{\circ} \mathrm{C} by a refrigerator?