Question

The resistances of the four arms P, Q, R and S in a Wheatstone's bridge are 10 ohm, 30 ohm, 30 ohm and 90 ohm, respectively. The e.m.f. and internal resistance of the cell are 7 volt and 5 ohm respectively. If the galvanometer resistance is 50 ohm, the current drawn from the cell will be

• A. 1.0 A
• B. 0.2 A
• C. 0.1 A
• D. 2.0 A

Answer 1

The correct option is B 0.2 A

Given circuit is balance wheatstone bridge.

$R_{eff}=\frac{40\times 120}{120+40}=30\Omega$
$l=\frac{7V}{(30+5)\Omega }=0.2A$