Question

When a galvanometer is shunted with a 4Ω resistance, the deflection is reduced to one-fifth. If the galvanometer is further shunted with a 2Ω wire. the further reduction (find the ratio of decrease in current to the previous current) in the deflection will be (the main current remains the same)

• A. (8/13) of the deflection when shunted with 4 Ω only
• B. (5/13) of the deflection when shunted with 4 Ω only
• C. (3/4) of the deflection when shunted with 4 Ω only
• D. (3/13) of the deflection when shunted with 4 Ω only

Answer 1

Answer: (A)

(8/13) of the deflection when shunted with 4 Ω only

Answer 2

R_g × = × 4

⇒ R_g = 16 Ω

Case II

16 I₁ = $\frac { 4 \times 2 } { 6 }$ (I–I₁) ⇒ I₁ = I/13

So decrease in current to previous current