Question

If the volume of an ideal gas changes from 10 m³ to 4 m³ at a constant pressure of 50 Pa. Then work done is-
1. -200 J
2. -300 J
3. -400 J
4. -100 J

Answer 1

Correct Answer - Option 2 : -300 J

Concept:

• First Law of Thermodynamics: It states that energy cannot be created or destroyed in an isolated system; energy can only be transferred or changed from one form to another.
• When heat energy is supplied to a thermodynamic system or any machine:  Two things may occur:
  • The internal energy of the system or machine may change.
  • The system may do some external work.

According to the first law of Thermodynamics:

ΔQ = ΔW + ΔU

Where ΔQ = Heat supplied to the system, ΔW = work done by the system, ΔU = change in internal energy of the system.

Work done is characterized by a change in volume of gas 

ΔW = P. Δ V 

Calculation:

Pressure is given as P = 50 pa

Δ V or change in volume is given as 10 m3 to 4 m3 

So, Δ V  = Final Volume - Initial Volume = 4 m³ - 10 m³ = - 6 m³

ΔW = P. Δ V 

ΔW = 50 Pa × - 6 m3 = - 300 Joule

So, work done is - 300J