Question

Consider a room that is initially at the outdoor temperature of 20°C. The room contains a 40-W light bulb, a 110-W TV set, a 300-W refrigerator, and a 1110-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

Heat transfer is the flow of heat due to temperature difference.

The rate of increase in the energy content of the room is 1560 W.

What is heat transfer?

Heat transfer is the flow of heat due to temperature difference. The heat flow from higher temperature to the lower temperature.

Given information-

Initial temperature of the room is 20 degree Celsius.

The room contains a 40-W light bulb, a 110-W TV set, a 300-W refrigerator, and a 1110-W iron.

The rate of increase in the energy of the room is the difference of energy increasing in the room and the energy leaving to the room.

Thus the rate of increase

$\dfrac{dE_{room}}{dt}=E_{in}-E_{out}$

Energy inside the room is the sum of all the energies increasing  as,

$\rm E_{in}=E_{light}+E_{refrigerator}+E_{TV}+E_{iron}$

As there is no heat transfer through the walls. Thus the energy leaving to the room is,

$E_{out}=0$

Thus put the values in the first equation as,

$\dfrac{dE_{room}}{dt}=E_{in}-E_{out}\\\dfrac{dE_{room}}{dt}=40++110+300+1110\\\dfrac{dE_{room}}{dt}=1560$

Thus the rate of increase in the energy content of the room is 1560 W.

Learn more about the heat transfer here;

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