Question

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.

Answer 1

Answer:

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 ($\dfrac{dE}{dt}$) = Rate of change of energy within the room ($E_{in} - E_{out}$).

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., $E_{out} = 0$.

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

$\dfrac{dE}{dt} = \dfrac{dE_{in}}{dt} = P_{in} = P_{bulb} + P_{TV} + P_{refrigerator} + P_{iron} = (40 + 110 + 300 + 1200)~W = 1650~W$