Question

Which of the following equipment does not work on the principle of Joule’s law?
$(A)$ Electric heater
$(B)$Electric iron
$(C)$Electric bulb
$(D)$Electric fan

Answer 1

Hint : This question can be solved only if one understands what Joule’s law is. When an electric current is passed through a wire, heat is generated. This generation of heat is due to the collision of electrons in the wire. The amount of heat generated and the factors or parameters that the heat generated is dependent upon is given by Joule’s law.

Complete step-by-step solution:
Joule’s law is a mathematical expression that denotes the rate at which the resistance in an electric circuit converts the electrical energy into heat energy.
The formula is given by ${\text{Q = }}{{\text{I}}^{\text{2}}}{\text{Rt}}$
Where \[Q\] is the amount of heat produced. It is expressed in Joules.
\[I\] is the current flowing through the wire whose unit is mentioned in Amperes.
\[R\] is the resistance of the circuit mentioned in ohms and
\[t\] is the amount of time taken for the current to pass through the wire. Time is mentioned in seconds.
$(A)$The electric heater is a device that converts current into heat. Hence this apparatus is based on the principle of Joule’s law.
$(B)$Electric iron is also another device that uses the principle of Joule's law. In this case, the electric current is converted into heat.
$(C)$When an electric current is supplied to a bulb, the filament heats up as a result of which light is generated. So here also the electric current is converted into heat.
$(D)$Basis on which the electric fan works is the conversion of an electric current into mechanical energy. Hence, in this case, the electric fan does not work on the basis of Joule's law.
So the correct option here is $(D)$. Electric fan.

Note: The heating effect is dependent on the resistance, time is taken for the current to flow through the wire and the current. If the resistance of the wire is large, more heat will be produced. Similarly greater the time and current greater will be the generation of heat. Heat is expressed in terms of Joules. The heating element of electric iron, electric heater is nichrome, which is an alloy of nickel and Chromium. As this element has high resistance it can be heated to high temperatures without undergoing oxidation.