Question

To find the resistance or a galvanometer by the half deflection method the following circuit is used with resistances R1=9970 Ω, R2 = 30 Ωand R3 = 0. The deflection in the galvanometer is d. With R3 =107 Ω the deflection changed to d2 The galvanometer resistance is approximately

Answer 1

Answer:

Explanation:

At initial condition, R3 = 0

Equivalent resistance of R2 & R3 = 30  Ω

When R3 =107 Ω & R2 = 30 Ω, then equivalent resistance should be 30/2

= 15 Ω

this will be when equivalent resistance , R(g) , R3 will be parallel to R2, we get resistance of 15 Ω

Let Rg - R3 = R(eq)

1/R2 + 1/R(eq) = 1/30 + 1/30 = 1/15

R(eq) = 30 Ω

∴ R3- Rg = 30

∴ 107 - Rg = 30

∴ Rg = 77 Ω