Joule's Law

Joule's Law

We know that the heating impact of electric current when it travels in a circuit is because of collision among electrons of wire. Specifically, what is the amount of heat generated during flow of current through a wire and what are the parameters and conditions it is based upon. To answer all these questions, Joule gave a formula that describes this phenomenon precisely, and called as Joule’s Law.

Joule’s Law of Heating

The heat that is generated because of the current flow in an electric wire is described in Joules. The mathematical expression of Joule’s law is as explained below.

Joule’s first law

The joule’s first law shows the relationship between heat produced by a flowing electric current through a conductor.

Q = I2 R T


Q indicates amount of heat,

I shows electric current

R is the amount of electric resistance in conductor

T denotes time

  • The amount of generated heat is proportional to wire’s electrical resistance when the current in the circuit and the flow of current is not changed.
  • The amount of generated heat in conductor carrying current is proportional to square of the current flow through the circuit, when the electrical resistance and current supply is constant.
  • The amount of heat produced because of the current flow is proportional to the time of flow, when the resistance and current flow is kept constant.

When all three situations are put together, the resulting equation is expressed as,

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Practise This Question

What will happen to the reflected ray, if the incident ray falls along the normal to the mirror?