Question

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 1

Given, the heat supplied by the electric heater is 100 W and the work performed by the system is 75 J/s  or 75 W.

Let W be the work performed by system and Q be the heat supplied by the system, so

Q=W+U

Here, U is the internal energy.

The above expression is the first law of thermodynamics.

Substitute the values in the above expression.

100=U+75 U=25 W

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