class 12 th physics meter bridge

1. Priyanka Jakhar
Physics Lecturer
GGIC Vijay Nagar
Ghaziabad U.P.
Meter Bridge
Class 12th

2. Meter Bridge
It is also known as slide wire bridge.
It is an instrument which works on the principle of a Wheatstone
bridge .
A meter bridge is used in finding the unknown resistance of a
conductor as that of in a Wheatstone bridge.
Principle:--
works on the principle of a Wheatstone bridge .
One Lateral pair of resistance is replaced with the straight wire of a
specific length of 1m uniformly across the section.
One pair contain a known resistances and other pair contain Unknow
resistance.

6. Construction of meter Bridge
Wire :-- Meter bridge consist of a one meter long manganin or eureka straight
wire with a uniform cross sectional area ,which is fixed on the wooden block.
wooden block :-- All the connections made on it.
Metal strips :--Two L shaped metal strips one and straight metal strip to make
the Wheatstone bridge.
Galvanometer :--The galvanometer is the device used for detecting the presence
of small current and voltage or for measuring their magnitude. The galvanometer
is mainly used in the bridges and potentiometer where they indicate the null
deflection or zero current.
jockey stick :--The jockey is used to slide on the bridge wire. It is a metal rod
with one end as knife edge.
Connecting wires :-- Use to complete the circuit to flow of current.
Resistance box :--resistance box is that the variable resistances are available at
one point. If any circuit requires variable resistances, then there is no need of
replacing the resistor.
Unknown resistance wire :-- A wire used to find the resistance.

8. The Meter bridge consists of a wire of length 100 cm and of uniform cross-sectional area
clamped between two thick metallic strips A and C.
● The metallic strip has two gaps across which two resistors R and X are connected.
● Here X is the unknown resistance whose value to be determined.
● X is the standard known resistance.
● A galvanometer is connected between the central metallic strip to the sliding jockey J, which
slides over Meter bridge wire.
● The four arms AB, BC, DA and CD (with resistances R, S, resistances of wires of length l and
( 100 - l ) form a Wheatstone bridge.
● If jockey is moving along the wire, when bridge is balanced.
● By measuring l, the unknown resistance R can be measured.
By Wheatstone s bridge P R
=
Q S
Where P = R Q = X R = ρ l / A S = ρ ( 100 - l ) / A
R RAJ
X RJB

9. R l
=
X ( 100 – l )
l
R = X ( )
( 100 – l )
A B
R.B (R) X
K
E
l cm 100 - l cm
G
J
( 100 – l )
X = R ( )
l
R ρ l / A
=
X ρ ( 100 - l ) / A

10. A B
R.B (R) X2
G
J
K
E
l cm 100 - l cm
X1
R ρ l / A
=
X ρ ( 100 - l ) / A
R l
=
X ( 100 – l )
l
R = X ( )
( 100 – l )
( 100 – l )
X = R ( )
l
X = X1 + X2
When two unknown resistance wire are in series

11. A B
R.B (R) X2
G
J
K
E
l cm 100 - l cm
X1
X1 X2
X =
+ X2X1
R ρ l / A
=
X ρ ( 100 - l ) / A
R l
=
X ( 100 - l )
l
R = X ( )
( 100 – l )
( 100 – l )
X = R ( )
l
When two unknown resistance wire are in parallel

12. The material of wire used in meter bridge is made of manganin or eureka due to
there high specific resistance or resistivity.
Thick copper strips are used in meter bridge because copper is a good
conductor of electricity.
Application of a meter bridge
• It is used to measure an unknown resistance
• It can be used for the or comparison of two unknown resistances .
Note :--
(i) Clean the connecting wires and the connecting points of meter bridge properly with sand
paper.
(ii) All connections should be neat and tight.
(iii) Balance point should lie between 30 cm and 70 cm.
(iv) Do not keep the jockey and the wire in contact for a long time.
(v) Hold the jockey perpendicular to the wire of meter bridge.