Thermodynamics Physics - Thermodynamics

If an average person jogs, he produces 14.5 × 103 cal/ min. This is removed by the evaporation of sweat. The amount of sweat evaporated per minute (assuming 1kg requires 580 × 103cal for evaparation) is

1. 0.25kg
2. 2.25kg
3. 0.05kg
4. 0.20kg

Which of the processes described below are irreversible?

1. The increase in temprature of an iron rod by hammering it.
2. A gas in a small cantainer at a temprature T₁ is brought in contact with a big reservoir at a higher temprature T₂ which increases the temprature of the gas.
3. A quasi-static isothermal expansion of an ideal gas in cylinder fitted with a frictionless piston.
4. An ideal gas is enclosed in a piston cylinder arrangement with adiabatic walls. A weight W is added to the piston, resulting in compression of gas.

A system goes from P to Q by two different paths in the P-V diagram as shown in Fig. Heat given to the system in path 1 is 1000J. The work done by the system along path 1 is more than path 2 by 100J. What is the heat exchanged by the system in path 2?

Air pressure in a car tyre increases during driving. Explain.

If a refrigerator’s door is kept open, will the room become cool or hot? Explain.

Consider a P-V diagram in which the path followed by one mole of perfect gas in a cylindrical container is shown in Fig.

Find the work done when the gas is taken from state 1 to state 2.

If the co-efficient of performance of a refrigerator is 5 and operates at the room temperature (27°C), find the temperature inside the refrigerator.

Can a system be heated and its temperature remains constant?

Consider a P-V diagram in which the path followed by one mole of perfect gas in a cylindrical container is shown in Fig.

Given the internal energy for one mole of gas at temperature T is (3/2) RT, find the heat  supplied to the gas when it is taken from state (1) to (2)  with V₂ = 2V_1.

The initial state of a certain gas is (P_i , V_i , T_i ). It undergoes expansion till its volume becoms V_f . Consider the following two cases:

1. The expansion takes place at constant temperature.
2. The expansion takes place at constant pressure.

Plot the P-V diagram for each case. In which of the two cases, is the work done by the gas more?

Is it possible to increase the temperature of a gas without adding heat to it? Explain.

Consider a Carnot’s cycle operating between T₁ = 500K and T₂=300K producing 1k J of mechanical work per cycle. Find the heat transferred to the engine by the reservoirs.

Consider one mole of perfect gas in a cylinder of unit cross section with a piston attached (Fig.) A spring (spring constant k) is attached (unstretched length L) to the piston and to the bottom of the cylinder. Initially the spring is unstretched and the gas is in equilibrium. A certain amount of heat Q is supplied to the gas causing an increase of volume from V_o to V₁.

1. What is the initial pressure of the system.
2. What is the final pressure of the system.
3. Uing the first law of thermodynamics, write down a relation between Q, P_a, V, V_o and k.

A cycle followed by an engine (made of one mole of an ideal gas in a cylinder with a piston) is shown in Fig. Find heat exchanged by the engine, with the surroundings for each section of the cycle. (C_v = (3/2) R)

AB : constant volume

BC : constant pressur

CD : adiabati

DA : constant pressure

In a refrigerator one removes heat from a lower temperature and deposits to the surroundings at a higher temperature. In this process, mechanical work has to be done which is provided by an electric motor. If the motor is of 1KW power, and heat is transferred from –3°C to 27°C, find the heat taken out of the refrigerator per second assuming its efficiency is 50% of a perfect engine.