question1.
a) A current 'I' is flowing through a resistor 'R' having potential difference 'V' across its ends and in time 'T' charge 'Q' flows. drive an expression for heat produced.
b) what will happen to heat produced if the current passing through an electric heater has been halved?
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Class 10
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>>Heating Effect of Electric Current
>>(a) Derive the expression for the heat p
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(a) Derive the expression for the heat produced due to a current 'I' flowing for a time interval 't' through a resistor 'R' having a potential difference 'V' across its ends. With which name is this relation known ?
(b) How much heat will an instrument of 12W produce in one minute if it is connected to a battery of 12V ?
(c) The current passing through a room heater has been halved. What will happen to the heat produced by it ?
(d) What is meant by the heating effect of current ? Give two applications of the heating effect of current .
(e) Name the material which is used for making the filaments of an electric bulb.
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(a) When an electric charge Q moves against a p.d. V, the amount of work done is given by
W=Q×V ---------------(1)
We know, current , I=
t
Q
Q=I×t ------------(2)
By ohm's law ,
I
V
=R
V=I×R --------------(3)
Putting eqs. (2) and (3) in eq. (1),
W=I×t×I×R
W=I
2
Rt
Assuming that all the electrical work done is converted into heat energy , we get
Heat produced , H=I
2
Rtjoules
This relation is known as Joule's law of heating.
(b) Given : P=12W,V=12V,t=60sec
using the equation of power
P=VI
I=P/V=12/12=1A
The Ohm's law states that
V=IR
R=V/I=12/1=12ohm
The formula for heat is:
H=I
2
Rt
H=1
2
×12×60
H=720J
(c) The heat produced by the heater will become one - fourth because heat produced is directly proportional to the square of the current.
(d) When an electric current is passed through a high resistance wire , the wire becomes very hot and produces heat. This effect is known as heating effect of current. This effect is used in room heaters and electric ovens.
(e) Tungsten is used for making the filaments of an electric bulb.
Answer:
(a.) When an electric charge Q moves against a p.d. V, the amount of work done is given by --
W = Q × V ------------(1)
We know, current , I = Q / t
Q = I × t ------------(2)
By ohm's law , I / V =R
V = I × R -----------(3)
Putting eqs. (2) and (3) in eq. (1),
W = I × t × I × R
W = I^2Rt
Assuming that all the electrical work done is converted into heat energy , we get
Heat produced , H=I^2Rt joules
This relation is known as Joule's law of heating.
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(b.) what will happen to heat produced if the current passing through an electric heater has been halved?
Sol-) The heat produced by the heater will become one - fourth because heat produced is directly proportional to the square of the current.
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