This document discusses the heating effect of electric current. It explains that when electric current passes through a conductor, the conductor gets heated due to the flow of electrons. This heating effect is called Joule heating. Joule's law states that the amount of heat produced is directly proportional to the square of the current, the resistance, and the time. The document also provides an example calculation using Joule's law to determine the potential difference across a resistor given the heat produced, resistance, and time. Finally, it defines electric power as the rate at which electric work is produced or consumed in a circuit.

1. Electricity
Class – 10
Instructor: A. K Mishra

2. HEATING EFFECT OF ELECTRIC CURRENT
Heating effect of electric current
• When an electric current is passed through the wire it gets
heated
• This effect due to flow of electric current through the
conductor is called heating effect of electric current.
• Amount of heat produced in the conductor or resistor is
obtained by Joule’s law of heating

3. JOULE’S LAW HEATING
• Heat produces in a resistor is directly proportional to
(i) square of the current flowing through the resistor
(ii) resistance for the given current
(iii) time
2
H = I R t (Joules)  
2
H I

H R

H t


4. DERIVATION
JOULES LAW HEATING EFFECT
Work done (W) = Heat energy dessipated (H)
H = W = V Q

 
= V I t
 
= IR I t
2
H = I R t
• Let ‘ I ’ is a current flowing through resistor R
• Let V be the potential difference across the resistor
• Let t is the time taken to by Q charges to flow across it
• Work done to move electrical charges, W or heat energy
dissipated or produced during time t

5. PROBLEMS
Q.1 100 joules of heat is produced each second in a 4 ohms of
resistance. Find the potential difference across each resistor?
Ans: Given:
H = 100 J
R = 4 Ω
t = 1 s
To find :
Potential difference (V) = ?
Solution :
We from joules law of heating ,
2
H = I R t
2 H
I =
R t
2
H
=
R t
V
R
 
 
 
2
2
V H
=
R R t
2 H R
V =
t

2 100 4
V =
1

V = 400 20 volts

V
I = , ohms law
R
 
 
 

6. PROBLEMS
Q.2 An electric iron of resistance 20 ohms takes a current of 5 A.
Calculate the heat developed in 30s.
Ans: Given:
I = 5 A
R = 20 Ω
t = 30 s
To find :
Heat produced (H) = ?
Solution :
We from joules law of heating ,
2
H = I R t
2
H = (50) 20 30
 
H = (2500) 600

H =1500000 J
H =1500 kJ

7. POWER
Power :
• Rate of doing work is called power
• Work done per unit time
work done
Power =
time
W
P =
t

8. Electric power
Electric power :
• Rate at which electric work is produced or consumed in an
electric circuit is called electric power
Electric work done
Electric power =
time
W
P =
t
 
V Q
=
t
 
V I t
=
t
P = V I
P = V I
P = (IR) I
2
P = I R
P = V I
V
= V
R
 
 
 
2
V
P =
R
( V= I R)
V
( V= I R , I = )
R