Question

A student connects four cells, each of internal resistance $\frac{1}{4}\Omega$, in series. One of the cells is incorrectly connected because its terminals are reversed. The value of external resistance is $1\Omega$. If the emf of each cell is 1.5 volt then current in the circuit will be

• A. $\frac{4}{3}A$
• B. $0$
• C. $\frac{3}{4}A$
• D. $1.5A$

Answer 1

The correct option is D $1.5A$

The cells are connected in series hence, the equivalent of internal resistances of cells is

$r=\frac{1}{4}+\frac{1}{4}+\frac{1}{4}+\frac{1}{4}$

$r=\frac{4}{4}=1\Omega$

One of the cells is incorrectly connected because its terminals are reversed.

The cell has equal emf hence in series total emf is

$E=1.5-1.5+1.5+1.5=3V$

Let, the external resistance is, $R=1\Omega$

The current in circuit is

$I=\frac{E}{R+r}$

$I=\frac{3}{1+1}$

$I=\frac{3}{2}=1.5A$