Page 52 - Physics_Form_2

Physics for Secondary Schools

When resistors are connected in parallel, For identical n resistors connected in
the p.d. across each resistor is the same parallel, R = R = R = ... R= = . R The
n
1
2
3
as the total voltage in the circuit. Though reciprocal of total resistance is given by
the voltage is the same for all branches,
the currents flowing in each branch are 1 = n . Therefore, the total resistance is
different. Thus, Ohm’s law can be applied R T R
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in each branch. To find the different given by R = R .
currents, one considers the current through T n
each junction. The sum of the currents in It should be noted that when resistors are
each resistor in Figure 2.10 equals the total connected in series, their total resistance
current in the circuit. That is, is higher than that of individual resistors.
I = I + 1 I + 2 I 3 However, for resistors connected in

From Ohm’s law, the current, I, in the parallel, the total resistance is lower than
that of individual resistors. Activity 2.2
circuit is given by, will help in practical learning on effect of
V arrangement of resistors.
I = R T

Where, R is the equivalent resistance. Activity 2.2
T
Aim: To investigate the effective
Applying Ohm’s law to each resistor resistance for resistors in
gives: series and in parallel
V = V + V + V
R R R R Materials: two dry cells of 1.5 V each,
1
2
T
3
connecting wires, bulbs
V  V  1  1  1  Procedure
R T   R 1 R 2 R 3   1. Connect two cells, each of 1.5 V in
series and then connect them to one
Therefore, of the bulbs, A, as shown in Figure
1 = 1 + 1 + 1 2.11

R T R 1 R 2 R 3
3 v
When resistors are connected in parallel,
the reciprocal of the total resistance is
equal to the sum of the reciprocals of the
individual resistances. Generally, when
n resistors are connected in parallel, the
reciprocal of the equivalent resistance is
given by, Bulb A

1 1 1 1 1
= + + ++ Figure 2.11
...
R T R 1 R 2 R 3 R n Observe the brightness of the bulb.

46
Student’s Book Form One

Physics Form 2 Final.indd 46 25/10/2025 10:25