The metre bridge wire A B shown in the adjoining figure is 100 cm long. When A D = 30 cm , no deflection occurs in the galvanometer. What is the value of R (in ohm)?

Step-by-step solution

Let ρ be the resistance per unit length of the metre bridge wire. From the condition of balance of Wheatstone bridge. P Q = R S ⇒ 6 R = 30 ρ 100 - 30 ρ = 30 70 = 3 7 ⇒ R = 7 × 6 3 ⇒ R = 14 Ω