Key idea

The terminal potential difference of a cell is $V = E - Ir$ when the cell is supplying current, where:

• $E$ = emf of the cell
• $r$ = internal resistance
• $I$ = current in the circuit

From the circuit

For the given cell:

• emf $E = 3\,\text{V}$
• internal resistance $r = 1\,\Omega$
• external resistance $R = 2\,\Omega$

So total resistance in the circuit is $R_{\text{total}} = R + r = 2 + 1 = 3\,\Omega$

Find the current

Using Ohm’s law for the whole circuit: $I = \frac{E}{R+r} = \frac{3}{3} = 1\,\text{A}$

Find terminal potential difference

$V = E - Ir = 3 - (1)(1) = 2\,\text{V}$

Alternatively, terminal voltage across the external resistor is $V = IR = (1)(2) = 2\,\text{V}$

Match with options

$2\,\text{V}$ corresponds to Option C.

Comparison with stored answer

Stored correct answer: C
Derived answer: C
Hence, they agree.