Page 30 - Physics - XII

Table for fi gure of merit

S. E.M.F. of the cell Resistance from Defl ection in the Figure of merit
No. E resistance box galvanometer E
(volt) R θ θ K= (R+ G )θ
(Ω) (divisions) (amp./div.)

1.

2.

3.
4.

Mean K = _____ amp./div.

Calculations

1. Calculations for Galvanometer Resistance G: Calculate the value of G by using the formula
RS
G =
RS

2. Calculation for Figure of Merit K:
E
K =
( RG)

Result
1. The resistance of the given galvanometer by half-defl ection method is G = _____ Ω.
2. Figure of merit, K = _____ ampere/division.

Precautions
1. All the connections should be neat, clean, and tight.
2. All the plugs in both the resistance boxes should be tight.

3. First the high resistance R from the resistance box should be introduced, then the battery key K plug
1
should be inserted to avoid any damage to the galvanometer.
4. The e.m.f. of the battery should be constant.
5. The value of R should be large as compared to G.

Sources of Error
1. The plugs of the resistance boxes may not be clean and tight.
2. The e.m.f. of the battery may not be constant.
3. The galvanometer divisions may not be equal.

EXPERIMENT - 5(a)

Aim
To convert the given galvanometer (of known resistance and fi gure of merit) into a voltmeter of desired
range and to verify the same.

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