The resistances of the four arms P, Q, R and S in a Wheatstone's bridge are 10 , 30 , 30 and 90 , respectively. The emf and internal resistance of the cell are 7 ~V and 5 respectively. If the galvanometer resistance is

Correct answer: B. 0.2 ~A Effective resistance, R_ eff =(40 × 120)/(120+40)=(4800)/(160)=30 Current =(7)/((30+5))=(7)/(35)=0.2 ~A [ i=(E)/(R+r)]

NEET 2013

NEET 2013 · Physics · Current Electricity

The resistances of the four arms P, Q, R and S in a Wheatstone's...

The resistances of the four arms

P, Q, R

and

S

in a Wheatstone's bridge are

10 \Omega, 30 \Omega, 30 \Omega

and

90 \Omega

, respectively. The emf and internal resistance of the cell are

7 \mathrm{~V}

and

5 \Omega

respectively. If the galvanometer resistance is

50 \Omega

, the current drawn from the cell will be

B. $0.2 \mathrm{~A}$

Effective resistance,

R_{\text{eff }}=\frac{40 \times 120}{120+40}=\frac{4800}{160}=30 \Omega

\therefore

Current

=\frac{7}{(30+5)}=\frac{7}{35}=0.2 \mathrm{~A}

\left[\because i=\frac{E}{R+r}\right]