Question

Two batteries of emfs $2\, V$ and $1 \,V$ of internal resistances $1 \Omega$ and $2 \, \Omega$ respectively are connected in parallel. The effective emf of the combination is

• A. $\frac {3}{2} V$
• B. $\frac {5}{3} V$
• C. $\frac {3}{5} V$
• D. 2 V

Answer 1

Answer: (B)

$\frac {5}{3} V$

Answer 2

$\, \, \, \, \, \, E_{eff} = \frac {E_1r_2 + E_2r_1}{r_1 + r_2 }$ $\frac {(2 \times 2) + (1 \times 1)} {(2 + 1)}$ $= \frac {4 + 1} {3} = \frac {5}{3}V$