[R.H.S]
Expt. No. 4
METRE BRIDGE 3
AIM :
To verify the laws of combination of resistances in parallel using a meter
bridge.
APPARATUS:
Meter bridge, galvanometer, one way key, a resistance box, battery, jockey, two
unknown resistance wires, and connecting wires.
THEORY:
The effective resistance XP of the combination of two resistors when connected in
parallel can be calculated by :
XP =
-----------(i)
The resistance (X ) of a resistor is given by:
X=
-----------(ii)
Where ‘l’ is the balancing length and R, the known resistance.
PROCEDURE:
(i) Measure the unknown resistances X1and X2 separately using the procedure
explained in experiment 2, after making the suitable connections as done in
experiment 2. Here you can find the value of unknown resistances without
interchanging the R. B. and unknown wire in the gaps.
(ii) After finding the value of X1 and X2, connect the two in parallel as shown
below in figure.
(iii) Proceed in the same way as in experiment 2. Take at least three sets of
observations for balance point lying between 30 cm and 70 cm.
(iv) Calculate the effective resistances using equation (ii).
(vi) Compare the measured values of effective resistances using Meter Bridge with
the calculated values.
RESULT
The value of unknown resistances X1 =
 and
The value of effective resistance in parallel:
By calculation =

By experiment,

X2 =
=

Hence the law of combination of resistances in parallel is verified.
Precautions and sources of error:
(same as expt 2)
[L.H.S]
CIRCUIT DIAGRAM;
OBSERVATIONS:
(i) To find X1
(ii) To find X2
(ii) To find XP (parallel combination of X1 and X2)
VERIFICATION:
XP =
From observations:

=
XP =

Thus the law of parallel combination of resistors is verified.