Ncert Exercises & Solutions

Which of the processes described below are irreversible?

a.	The increase in temperature of an iron rod by hammering it.
b.	A gas in a small container at a temperature T 1 is brought in contact with a big reservoir at a higher temperature T 2 which increases the temperature of the gas.
c.	A quasi-static isothermal expansion of an ideal gas in a cylinder fitted with a frictionless piston.
d.	An ideal gas is enclosed in a piston-cylinder arrangement with adiabatic walls. A weight w is added to the piston, resulting in the compression of gas.

Choose the correct alternative/s:

1. (a, b, c)

2. (a, d)

3. (b, c, d)

4. (a, b, d)

(4) Hint: The reversible processes are those which can be reversed through the same conditions by themselves.

Step 1: Find if the processes can be reversed through the same conditions by themselves.

1. When the rod is hammered, the external work is done on the rod which increases its temperature. The process cannot be retraced itself.

2. In this process energy in the form of heat is transferred to the gas in the small container by the big reservoir at temperature

T_{2}

. It can not be reversed itself.

4. As the weight is added to the cylinder arrangement in the form of external pressure, hence, it cannot be reversed back itself.