First Law of Thermodynamics

Which of the following is equivalent to the principle of energy conservation?

• Newton’s first law

• The first law of thermodynamics

• Newton’s second law

• The second law of thermodynamics

An ideal gas undergoes the thermodynamic changes represented in the P –V diagram below

(P → Q → R → P).

Which of the following is the net work done by the gas in a cycle?

• 4.5 × 10⁵ J

• 3.0 × 10⁵ J

• 1.0 × 10⁵ J

• Zero

The diagram shows the pressure-volume relationship for a fixed mass of an ideal gas that undergoes a cycle XYZ.

In which part(s) of the cycle is external work done on the gas?

• Y → Z only

• Y → Z and Z → X only

• X → Y and Z → X only

• X → Y only

The diagram shows the pressure–volume (PV) relationship for a gas.

Which of the following area(s) is/are equal to the work done by the gas as it expands?

• area I

• area II

• area I + area II

• area I – area II

The diagram shows the pressure/volume (p/V) diagram for one cycle PQRS of an engine.

In which sections of the cycle is work done on the engine?

• SP only

• PQ only

• SP and PQ only

• RS and SP only

The first law of thermodynamics states that ΔU the change in internal energy of a system is related to the heat Q supplied to it and W the work on it by the equation:

ΔU = Q + W

What are ΔU, Q and W for a constant mass of ideal gas whose temperature is decreased at constant pressure?

• A

• B

• C

• D