Transcript CHAPTER – 14 Electric current and its Effects

Electricity
Heating effect of Electric Current
Heating effect of electricity is one of the widely
used effects in the world. When electric current is
passed through a conductor, it generates heat due
to the resistance it offers to the current flow. The
work done in overcoming the resistance is
generated as heat.
Electricity
Heating effect of Electric Current
The heat (H) produced by a heating element is:
(i) directly proportional to the square of the
electric current (I) passing through the
conductor.
(ii) directly proportional to the resistance (R) of the
conductor.
Electricity
Heating effect of Electric Current
(iii) directly proportional to the time (t) for which
the current flows through the resistor.
It is given by the expression H = I2Rt and is well
known as Joule’s Law.
Electricity
Heating effect of Electric Current
Practical Applications of Heating Effect of Electric Current
 The heating effect of
electric current is used in
electrical appliances like
electric heater, electric
iron,
electric
room
heater, immersion heater,
electric kettle, hair dryer
etc.
Electricity


Heating effect of Electric Current
All these appliances have a coil of wire called
an element. When electric current flows
through the element it becomes hot and gives
out heat.
The amount of heat produced in a wire
depends upon its material, length and
thickness.
Electricity
Heating effect of Electric Current
Electric Fuse
Electric fuse is a safety device used in electrical
circuits which protects the electrical circuits and
appliances and prevents fires. Electric fuse has a
wire which melts quickly and break when large
electric current flows through it.
Electricity
The fuses used for domestic purposes are rated as
1 A, 2 A, 3 A, 5 A, 10 A, etc. For an electric iron
which consumes 1 kW electric power when
operated at 220 V, a 5 A fuse must be used.
Electricity
Heating effect of Electric Current
Example
An electric kettle consumes energy at a rate of 840
W when heating is at the maximum rate and 360 W
when the heating is at the minimum. The voltage is
220 V. What are the current and the resistance in
each case?
Solution
The power input is P = V I
Thus the current I = P/V
(a) When heating is at the maximum rate,
I = 840 W/220 V = 3.82 A;
Electricity
Heating effect of Electric Current
and the resistance of the electric kettle is
R = V/I = 220 V/3.82 A = 57.60 Ω.
(b) When heating is at the minimum rate,
I = 360 W/220 V = 1.64 A;
and the resistance of the electric kettle is
R = V/I = 220 V/1.64 A = 134.15 Ω.