To find resistance of a given wire using Whetstone’s bridge (meter bridge) & hence determine the specific resistance of the material.
A meter bridge (slide Wire Bridge), a galvanometer, a resistance box, a laclanche cell, a jockey, a one- way key, a resistance wire, a screw gauge, meter scale, set square, connecting wires and sandpaper.
X= (100-ι)/ιx R where
R = known resistance placed in left gap.
X = Unknown resistance in right gap of meter bridge.
ι=length of meter bridge wire from zero and upto balance point (in cm)
Where,
D: Diameter of given wireL:Length of given wire.
S.No. | AResistance from resistance box R (ohm) | Length AB = ι cm | Length BC = (100-l) cm | Unknown Resistance X=R. (100-ι)/ιΩ |
1 | 2 | 41 | 59 | 2.87 |
2 | 4 | 60 | 40 | 2.66 |
3 | 6 | 69 | 31 | 2.69 |
S.No. | Linear Scale Reading (N) mm | No. of circular scale divisions coinciding (n) | Value n x (L.C.) mm | Observed diameter D = N + n x L.C.mm |
1 | 0 | 34 | 0.34 | 0.34 |
2 | 0 | 35 | 0.35 | 0.35 |
3 | 0 | 36 | 0.36 | 0.36 |
4 | 0 | 35 | 0.35 | 0.35 |
For unknown resistance, X:
Mean X = X_{1}X_{2}+ X_{3}+ X _{4} / 4 = 2.68Ω
Mean diameter, D= D_{1}D_{2}+ D_{3}+ D _{4} / 4 =0.035cm
Mean X = X_{1}X_{2}+ X_{3}+ X _{4} / 4 = 2.68Ω
Specific Resistance, ρ= X.πD _{2}/4L=1.03 x 10 ^{-4}Ωcm
Value of unknown resistance = 2.68Ω
Specific resistance of material of given wire = 1.03 x 10 ^{-4}Ωcm
All plugs in resistance box should be tight. Plug in key, K should be inserted only while taking observations.
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