class 10 cbse science physics electricity joules law of heating

1. Electricity
Class – 10
Aditya Mishra
Email: adityakumar2009@gmail.com
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2. JOULE’S LAW HEATING
• Heat produces in a resistor is directly proportional to
(i) square of the current flowing through the resistor
(ii) resistance of resistor for the given current
(iii) time for which current is flowing through it
2
H = I R t (Joules)
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3. POWER
Power :
• Rate of doing work is called power
• Work done per unit time
work done
Power =
time
W
P =
t
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4. Unit of Power
Watt :
• Power consumed by a device carrying 1 A of current when
operated at a potential difference of 1V
• SI unit of Power
P = V I
1 watt = 1 Volt 1 Ampere

Work done
Power =
time
 
joules J
=
second (s)
= W
J
=
s
 
 
 
2
Kg m
s

= N
N m
 = J
N m J
=
s s
 = W
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5. COMMERCIAL UNIT OF ELECTIC ENERGY
Commercial unit of power :
• kilowatt-hour (kWh)
• Commonly used unit of power in daily life
• Electrical equipment's (e.g. bulb, tube light, battery, heater ) are
rated on commercial units of power
1 kWh = 1000 Wh
= 1000 x J/s x 3600 s
= 3600000 J
= 36 x 105 J
= 3.6 x 10 6 J
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6. PROBLEMS
1. An electric bulb is connected to a 110 V generator. The current
is 0.25 A. Find the power of the bulb?
Ans :
Given :
V = 110 V
I = 0.25 A
To find :
Power = ?
Solution :
we know that electrical power
P = V I
= 110 x 0.25
= 27.5 Watt
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7. Power :
• Rate of doing work is called power
• Work done per unit time
work done
Power =
time
W
P =
t
PROBLEMS
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