Consider a room that is initially at the outdoor temperature of 208C. The room contains a 40-W lightbulb, a 110-W TV set, a 300-W refrigerator, and a 1200-W iron. Assuming no heat transfer through the walls, determine the rate of increase of the energy content of the room when all of these electric devices are on.

The rate of increase of the energy content of the room when all the eletrical devices are on is 1650 W.

Explanation:

From conservation of energy,

Rate of energy transfer () = Rate of change of energy within the room ().

As according to the problem no heat transfer occurs through the walls of the room we can assume that there is no energy transferred to the outside of the room, i.e., .

If all the electric devices are on inside the room, then the rate of increase of energy is equal to the power () consumed bt the electrical devices inside the room. Therefore we can write,