Question

Under what condition terminal potential difference is less than emf?

Answer 1

The terminal potential difference (V) will be less than the EMF (E) of a source when there is a current flowing through the circuit and the internal resistance (r) of the power source is non-zero.

Here's why:

1. The EMF of a source (like a battery or a generator) is the maximum potential difference when no current is flowing. It is the energy per unit charge supplied by the source.
   

1. The terminal potential difference (V) is the potential difference across the terminals of the source when a current is flowing through the circuit.
   

When current flows, the power source has internal resistance (r). This causes a voltage drop inside the source, and the terminal potential difference will be reduced. The relationship is given by:

\[
V = E - I \cdot r
\]

Where:

1. \( E \) is the EMF of the source,
   

1. \( I \) is the current flowing through the circuit,
   

1. \( r \) is the internal resistance of the source,
   

1. \( V \) is the terminal potential difference.
   

So, for the terminal potential difference to be less than the EMF, a current must be flowing and the internal resistance must be non-zero. The greater the current or the internal resistance, the more the terminal potential difference will drop below the EMF.