CBSE Class 12 · 2013 · Delhi · Current ElectricityShort Answer

Define the current sensitivity of a galvanometer and write its SI unit. The figure shows two circuits, each with a galvanometer and a

3 V

battery. When the galvanometers show no deflection, obtain the ratio

R_{1} / R_{2}

Solution

Current sensitivity is the deflection produced per unit current,

I_{s} = \frac{θ}{I} = \frac{N A B}{k}

. No deflection means each arm is a balanced potential divider: the first circuit gives

\frac{4}{R _{1}} = \frac{6}{9} \Rightarrow R_{1} = 6 Ω

, the second

\frac{12}{8} = \frac{6}{R _{2}} \Rightarrow R_{2} = 4 Ω

, so

\frac{R _{1}}{R _{2}} = \frac{6}{4} = \frac{3}{2} .

CBSE Class 12 Board · 2013 · Delhi · Subjective