Problem

The current in a circuit with an external resistance of

3.75 \Omega

0.5 \text{ A}

. When a resistance of

1 \Omega

is introduced into the circuit, the current becomes

0.4 \text{ A}

. The emf of the power source is a.

1 \text{ V}

2 \text{ V}

3 \text{ V}

4 \text{ V}