To determine the resistance of a galvanometer by half-deflection method & to find its figure of merit.
A Weston type galvanometer, a voltmeter, a battery, a rheostat, two resistance boxes (10,000Ωand 500Ω), two one-way keys, a screw gauge, a meter scale, connecting wires and a piece of sandpaper.
G=R.S/R-S
Where R: resistance connected in series with the galvanometer
S: shunt resistance
Where E : emf of the cell θ:deflection produced with resistance R.
Sr. No. | Resistance R (Ω) | Deflection in galvanometer (θ) | Shunt Resistance S (Ω) | Half Deflection θ/2 | Galvanometer Resistance G=RS/R-S(Ω) |
1 | 4500 | 30 | 70 | 15 | 71.1 |
2 | 9500 | 14 | 70 | 7 | 70.5 |
3 | 5200 | 26 | 70 | 13 | 70.9 |
4 | 5700 | 24 | 70 | 12 | 70.8 |
Take mean of all values of G recorded in table.
Take mean of values of k.
Sr. No. | EMF of the Cells E(v) | Resistance from R.B. R Ω | Deflection θ(div.) | Figure fo Merit K=E/(R+G)θ |
1 | 1.5x2 = 3 | 4500 | 30 | 2.18 x 10 ^{-5} |
2 | 3 | 9500 | 14 | 2.23 x 10 ^{-5} |
3 | 3 | 5200 | 26 | 2.18 x 10 ^{-5} |
4 | 3 | 5700 | 24 | 2.16 x 10 ^{-5} |
Mean k= 2.19 x 10 ^{-5} A/div.
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