Page 67 - Physics_Form_2
P. 67
Current electricity
circuit to an equivalent resistance using At this point, the bridge circuit is
parallel and series formulae. However, balanced, and therefore,
if you observe the circuit carefully, you P R
realize that, the resistors on one side of Q = X V ,
the joint resistor, J, are in the same ratio
as the resistor on the other side of J. That which means,
FOR ONLINE READING ONLY
is, QR
X = V
P 5 R 10 P
and 5.
Q 1 X 2 Performing activity 2.7 gives more
understanding on Wheatstone bridge.
P R
Therefore, = .
Q X
Activity 2.7
A bridge circuit that has this property is
said to be a balanced Wheatstone bridge. Aim: To determine the resistance
Now, suppose the resistor J, is removed of an unknown resistor X,
from the circuit so that resistor P, is in using a Wheatstone bridge.
series with resistor R, and resistor Q is Materials: zero centred galvanometer,
in series with resistor X. Moreover, the a dry cell, decade resistance
resistors P and R are in parallel with box R , known resistors P
V
resistors Q and X. Therefore, the voltages and Q (ranging from 1
at points E and F are the same. Since, Ω to10 Ω), the unknown
P R resistor X whose values
= , range from 4 to 10 ,
Q X
a switch, and connecting
the voltage drop at P is the same as the wires
voltage drop at Q, meaning that voltage Procedure
at point B (V is the same as voltage at 1. Use the materials provided to set
)
B
point C (V C ).This means the potential up the Wheatstone bridge circuit as
difference between points B and C is zero. shown in Figure 2.29.
Thus, when the resistor J is connected, 2. Switch ON the circuit to allow
current through it is zero. That is, when current to flow through the circuit.
the bridge circuit is balanced, I = 0 A. Ensure that the amount of current
J
Suppose a resistor J is replaced with a flowing through the galvanometer
galvanometer G as shown in Figure 2.29. does not deflect it out of range.
The variable resistor R can be varied 3. Adjust the resistance, R , until the
,
V
reading on the galvanometer, G
V
to a point where the current through the is zero. At this point the bridge is
galvanometer I = 0 A. balanced.
G
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Physics Form 2 Final.indd 61 25/10/2025 10:26
