Question

Question 21:
(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 12 W produce in one minute if it is connected to a battery of 12 V ?
(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.

Lakhmir Singh Physics Class 10

Answer 1

a. work done w = potential difference V × charge q .....3

by ohm's law , V = IR .....1

q =It ......2

substitute 1,2 in 3

w= V × q

w= IR × It

w= l2 ( I square) Rt

according to joules law ,

W= H,

I 2 (i square) Rt

Answer 2

Explanation:

A) Resistance =R

Current = I

Time=t

So, heat produced $=I^{2} R t$

It is called "Joule’s law of heating" effect of current.

B) Heat produced$=V I t=12 \times 1 \times 60=720 J$

C) Heat produced in the heater depends on the current as H $=I^{2} R t$ where H is heat and I is current. So as current is halved, heat becomes 1/4 th.

D) Heating effect of current says that when current is passed through a resistance, it leads to formation of heat and thereby dissipation of energy. Applications are an electric heater and electric iron.

E) Tungsten is used to make filament of an electric bulb.