Page 102 - Physics 10_Float

CURRENT ELECTRICITY

combination.
If resistances R , R , R …….., R are connected in series, then ,
1 2 3 n
the equivalent resistance of the combination will be given by
R = R + R + R + ……..+ R n
3
e
1
2
Point to ponder!
Example 14.4: If two resistors of 6 kΩ and 4 kΩ are connected in
series across a 10 V battery, then find the following quantities:
(a) Equivalent resistance of the series combination.
(b) The current flowing through each of the resistance.
(c) Potential difference across each of the resistances.
Solution: Given that, R = 6 kΩ and R = 4 kΩ A bird can sit harmlessly on
1 2 high tension wire. But it must
(a) The equivalent resistance of the series combination is R = R +R 2 n o t r e a c h a n d g r a b
e
1
or R = 6 kΩ + 4 kΩ =10 kΩ neighboring wire. Do you
e
(b) If a battery of 10 V is connected across the equivalent know why?
resistance R , the current passing through it is given by
e
V 10 V
-3
I = = = 1.0 x 10 A = 1 m A
R e 10 kΩ
In the case of series combination same current would pass
through each resistance. Hence, current through R and R
2
1
would be equal to1 mA.
-3
(c) Potential difference across R = V = R = 1.0 x 10 A × 6 kΩ = 6 VI
1
1
Potential difference across R = V = R = 1.0 x 10 A × 4 kΩ = 4 VI 2 -3
2
2
(ii) Parallel Combination
In parallel combination one end of each resistor is connected
with positive terminal of the battery while the other end of
each resistor is connected with the negative terminal of the
battery (Fig.14.13). Therefore, the voltage is same across R 1
each resistor which is equal to the voltage of the battery i.e., I 1 I R 2
2
V = V = V = V
3
1
2
I I R 3
3
Equivalent Resistance of Parallel Circuit
In parallel circuit, the total current is equal the sum of the K + V – I
currents in various resistances i.e., Fig 14.13: Three resistors in
= + + I I 1 I 2 I 3 ......... (14.9) parallel combination
Since the voltage across each resistance is V, so by Ohm's law

V V V
I = , I = and I =
1
R 1 2 R 2 3 R 3

102 Not For Sale – PESRP