Question

An electric fan becomes warm if used continuously because
a) A part of source energy is used to useful work
b) A part of source energy is converted into heat
c) Ohm's law of electric current
d) A part of source energy is used to rotate the blades,​

Answer 1

Answer: option b

Explanation:because some amount of energy is lost in the former of heat.

All energy is not used as mechanical energy

Some amount is used to generate heat.

Answer 2

An electric fan becomes warm if used continuously because d) A part of source energy is used to rotate the blades.

Explanation:

• A fan becomes hot when used continuously because part of the electrical energy is used to drive the fan while the part is dissipated as heat. So if we use it consistently, there is a continuous heat dissipation which heats the fan. It is based on "Law of Conservation of Energy".
• Energy can neither be created nor destroyed, so if the fan was putting 100W of energy into the airstream at the inlet, that 100W had to be accounted for to keep the balance.
• Some of the kinetic energy of the moving air was converted into thermal energy, slightly warming the equipment and the exhaust air, and the heat comes from the friction of the fan blades churning the air.
• This effect is small but real, and over time this theoretically "perfect" room would become quite hot.
• A fan becomes hot when used continuously because part of the electrical energy is used to drive the fan while the part is dissipated as heat.
• So if we use it continuously, there is a continuous heat dissipation which heats the fan.

Based on explanation option d is correct.

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