Question

The emf of a cell is always greater than its terminal voltage why? Give reason.

Answer 1

Hint: In emf, the maximum potential difference is obtained between the two electrodes of the cell when there is zero current drawn from the cell that is connected in an open circuit whereas terminal voltage is the potential difference across the terminals of a cell when it is switched on.

Formula Used:
 The emf ( $E$ ) and the terminal voltage ( $V$ ) can be related by,
$v=E-Ir$
Where,
$E$ is the emf of the cell
$V$ is the terminal voltage
$I$ is current
$r$ is internal resistance of the cell.

Complete step by step answer:
The terminal voltage is the potential difference across the terminals of a cell when it is switched on.
Voltmeter is a device in which the voltage output can be measured across its terminal. Terminal voltage can be measured by the voltmeter. Terminal voltage can be calculated by the, $v=E-Ir$
Emf has the maximum potential difference compared to terminal voltage, it can be delivered where there is no current flow in the circuit. Emf of a cell can be measured by the potentiometer.
The emf ( $E$ ) and the terminal voltage ( $v$ ) can be related by,
$E=v+Ir$
Where,
$E$ is the emf of the cell
$v$ is the terminal voltage
$I$ is the current
$r$ is the internal resistance of the cell.
The emf of a cell is greater than terminal voltage because the potential difference between the two terminals is not connected to any of the circuit. If it connects to the circuit then the voltage is automatically reduced because of the internal resistance.

Note: Emf can act as the charge pump to maintain its potential difference by moving the negative charge to the positive terminal, and positive terminal to negative terminal because to maintain its potential difference.