The document describes an experiment to convert a Weston-type galvanometer into an ammeter. Key steps include: 1. Connecting the galvanometer and other circuit components like a battery, resistance box, and keys. 2. Taking readings at half deflection to calculate the galvanometer's resistance. 3. Using additional readings and calculations to determine the figure of merit and suitable shunt resistance value. 4. Cutting and connecting a wire to serve as the shunt resistance and verifying readings match the ammeter.

1. Experiment:
Convert Weston-type Galvanometer into ammeter.
Apparatus:
Galvanometer, high resistance box, voltmeter, battery, resistance box, rheostat, plug key,
ammeter, screw gauge, meter rod, sand paper and connecting wires.
Procedure:
Half deflection method:
Draw a neat circuit diagram
Connect the components with the help of connecting wire such that high resistance box R
is connected in series with galvanometer G, key K1, and battery B and galvanometer is
connected in parallel with fractional resistance box S through key K2.
Keeping keys K1 and K open note the zero reading of the galvanometer. Take out a very
high resistance of about 2000 ohms from the resistance box R. keeping the shunt circuit
open, close the key K1 and adjust the value of R to get a large deflection in the
galvanometer. Now, subtract the zero reading from this deflection reading to get correct
reading in divisions.
Keeping the value of R unchanged, close both the keys K1 and K2 and adjust the shunt
resistance S to reduce the deflection to one half of its original value. Note the reading and
the value of shunt resistance S.
Take a number of readings with different values of R and S. If S is very small as
compared to R then, G = S. The resistance of galvanometer may also be calculated by the
relation .
Figure of merit:
Determine the e.m.f of the battery or cell with a good voltmeter.
Connect the galvanometer to the cell through a resistance box and plug key.

2. Adjust the resistance from resistance box to get a large deflection in the galvanometer.
Note the deflection θ and resistance R.
Disconnect the shunt resistance S from the apparatus and find the value of Ig by using the
formula . Where, E is the e.m.f of the battery, 30 is the total number of
divisions on galvanometer, R is the resistance selected, θ is the defection on that
resistance and G is the resistance of the galvanometer.
Calculation of shunt:
Calculate the full scale current Ig = nk (where, n is the number of divisions on the
galvanometer scale between the middle point and one extreme end).
Knowing the range of conversion calculate the value of shunt resistance by the relation
in ohms.
Take a wire and measure its diameter at about ten different places and calculate its mean
radius.
Now calculate the length l of wire whose resistance is equal to the shunt resistance X by
the relation where, ρ is the specific resistance of the wire material.
Verification:
Cut the length of the given wire 2cms more than the calculated length to account for the
portion of length that is wrapped around the terminals.
Connect the wire across the galvanometer terminals and complete the circuit.
Put in the key K in position and adjust the resistance from the rheostat to obtain a
maximum deflection of the galvanometer. Read the galvanometer and also the
corresponding reading on the ammeter. Take five more readings for different values of R.
Observations and calculations:
Galvanometer resistance (half deflection method)
Galvanometer
Half resistance
High Shunt
Sr. No. Deflection θ deflection
resistance R resistance S
θ/2
Ω Divs. Divs. Ω Ω
1.
2.
3.
Mean value of G = . . . . . . . . . Ω.
Figure of merit.