Page 34 - Physics - XII

6. Now, note the value of specifi c resistance of the material of the wire used as a shunt resistance and
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calculate its length using the relation, l rS

7. Cut a length of the wire 3 cm more than calculated value, i.e. (l + 3) cm. Mark two points on the wire,
one cm away from each end. Connect this wire to the two terminals of the galvanometer such that the
marked points are just outside the terminal screws as shown in Fig. 5(b).2. This galvanometer with the
shunt wire will now work as an ammeter of required range I.

Verifi cation
8. Make the connections of the circuit diagram as shown in Fig. 5(b).2.
9. Note the least count of converted ammeter and
Battery
standard ammeter A. + – Key Rheostat
10. Close the key K and adjust the rheostat so that K
maximum resistance introduced in the circuit. + Ammeter
Note down the reading of converted ammeter A
–
and standard ammeter A and fi nd the diff erence Galvanometer
between the two readings if any.
11. Change the resistance in the circuit with the help G Converted

of rheostat and repeat the step 10for at least four Shunt ammeter
more observations to cover whole range of the S
ammeter. Fig. 5(b).2: Circuit diagram to verify the conversion
12. Note all the observations in the observation table. of galvanometer into an ammeter

Observations

1. Given resistance of the galvanometer = G = _____ Ω
2. Given fi gure of merit of the galvanometer = K = _____ ampere/division
3. Total number of divisions on either side of zero = n = _____

4. Current for full scale defl ection I = K·n = _____ ampere
g
5. Range of the required ammeter = I = _____ milliampere (mA) = _____ ampere
6. Least count of the screw gauge = _____ mm = _____ cm
7. Zero correction for the screw gauge, e = _____ mm = _____ cm
Observed diameter of the wire,
(a) d = _____ cm (b) d = _____ cm (c) d = _____ cm (d) d = _____ cm
4
3
1
2
d d d d
Mean observed diameter of the wire, d 1 2 3 4 = _____ cm
0
4
Mean corrected diameter of the wire = d = d – e = _____ cm
0
d
8. Mean corrected radius of the wire = =r = _____ cm
2
9. Specifi c resistance of the material of the wire ρ = _____ Ω cm

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