Page 101 - Physics 10_Float

CURRENT ELECTRICITY

bound inside atoms. Hence, current cannot flow through an
insulator because there are no free electrons for the flow of
current. Insulators have very large value of resistance.
Insulators can be easily charged by friction and the induced
charge remains static on their surface. Other examples of
insulators are glass, wood, plastic, fur, silk, etc.

14.9 COMBINATION OF RESISTORS

(i) Series combination (ii) Parallel combination
Resistors can be connected in two ways.

(i) Series Combination
In series combination, resistors are connected end to end V 1 V 2 V
(Fig. 14.12) and electric current has a single path through the 3
circuit. This means that the current passing through each
I R 1 R 2 R 3
resistor is the same.
.
( ) + –
Equivalent Resistance of Series Circuit K V
Fig.14.12: Three resistors in
The total voltage in a series circuit divides among the
series combination
individual resistors so the sum of the voltage across the
resistance of each individual resistor is equal to the total Do you know?
voltage supplied by the source. Thus, we can write as We use heating effect of an
V= V +V +V 3 ......... (14.6) electric current for different
2
1
where V is the voltage across the battery, and V , V , V are the purposes. For example, when a
3
1
2
current flows through the
voltages across resistors R , R and R respectively. If I is the filament of a bulb, it glows
2
1
3
current passing through each resistor, then from Ohm's law white hot and gives out light.
V= IR + R + RI I Electric heaters have very thin
1 2 3
V= (R +R +R )I ......... (14.7) wires that glow red hot when a
1 2 3 current flows.
We can replace the combination of resistors with a single
resistor called the equivalent resistance R such that the
e Quick Quiz
same current passes through the circuit. From Ohm's law is used as the
Which metal
V= I R e filament of an electric bulb?
Thus, Eq. (14.7) becomes Explain with reason.
I R = (R +R +R )I 1 2 3
e
R R +R +R= 1 2 3 ......... (14.8)
e
Thus, the equivalent resistance of a series combination is
equal to the sum of the individual resistances of the

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