### Q.8:- An electric heater supplies heat to a system at a rate of 100W. If system performs work at a rate of 75 Joules per second. At what rate is the internal energy increasing?

**Answer:-**

Heat is supplied to the system at a rate of 100 W.

∴Heat supplied, *Q* = 100 J/s

The system performs at a rate of 75 J/s.

∴Work done, *W* = 75 J/s

From the first law of thermodynamics, we have:

*Q* = *U* + *W*

Where,

*U* = Internal energy

∴*U* = Q –* W*

= 100 – 75

= 25 J/s

= 25 W

Therefore, the internal energy of the given electric heater increases at a rate of 25 W.