Question

The internal resistance of cell of e.m.f. $2V$ is $0.1$. It is connected to a resistance of $3.9$. The voltage across the cell is

• A. $2.71V$
  
• B. $1.95V$
  
• C. $1.68V$
  
• D. $0.52V$
  

Answer 1

The correct option is B $1.95V$

A resistor of resistance $3.9\Omega$ is connected in series with internal resistance of cell $0.1\Omega$.

Total resistance of the circuit $R^{\prime }=0.1+3.9=4.0\Omega$

Emf of cell $E=2V$

Current flowing in the circuit $I=\frac{E}{R^{\prime }}$

$\therefore$ $I=\frac{2}{4}=0.5A$

Thus voltage across the cell $V_{cell}=IR$ where $R=3.9\Omega$

$⟹$ $V_{cell}=0.5\times 3.9=1.95V$