Question

Four identical cells of emf $E$ and internal resistance $r$ are to be connected in series. Suppose if one of the cell is connected wrongly, the equivalent emf and effective internal resistance of the combination is

• A. $4E$ and $4r$
• B. $4E$ and $2r$
• C. $2E$ and $4r$
• D. $2E$ and $2r$

Answer 1

Answer: (C)

$2E$ and $4r$

Equivalent resistance in series connection $r_{eq}=r_1+r_2+r_3+r_4$

$\therefore$ $r_{eq}=r+r+r+r=4r$

Equivalent emf in series connection $E_{eq}=E_1+E_2+E_3-E_4$ (as one is connected wrong)

$\therefore$ $E_{eq}=E+E+E-E=2E$