Page 36 - CHAPTER-1 (Electricity)

CHAPTER 1

ELECTRICITY

• We observe, when an electric current is passed through a high

resistance wire-like nichrome wire, then the wire becomes very hot

and produces heat.

• In purely resistive circuits, the source of energy continuously gets

dissipated entirely in the form of heat.

• This is obtained by the transformation of electrical energy into heat

energy. E.g. electric heater, iron, etc.

(i) Joule’s law: Heating Effect of Current

I am assuming a conductor as a resistance wire which resists the flow

of current through it. So, work must be done by the current source for

continuous flow of the current.

Now, we calculate the work done by the source when the current

flows through a wire of resistance . When an electric charge moves

against a potential difference . Then,

Amount of work, W=q×V

According to the definition of current, we can say,
q
I= ⟹q=I×t
t

From Ohm’s law,
V

I =R or V=IR

Substituting the values of and , we get,

2
W=qV=(It)(IR)=I Rt
Assuming that all electrical work done or electrical energy consumed

is converted into heat energy, i.e. heat produced. So, heat produced

is given by,

2
H=I Rt Thus, it is known as Joule’s law of heating.

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