Voltage, Emf and Potential difference

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Concept of Voltage, Emf and Potential difference (P.d)

Emf > Pd
Emf =  Potential Difference + Voltage drop (Ir)

Definition

Voltage is the electric pressure developed across two points which drives free electrons of a substance in a particular direction.

The voltage of cell or source is called electromotive force and voltage between any two points in a closed circuit is called potential difference.

The unit of voltage Emf or p.d is same Volt (V).

1 Volt is defined as the voltage applied across the resistance of 1 ohm carrying a current of 1 A. Voltage is measured by Volt meter and Voltmeter is always connected in parallel with load and source as shown in figure because they have very high resistance, hence can prevent the flow of current if connected in series

Difference between EMF and Potential Difference

EMF	Potential Difference
1. EMF refers voltage of source of electricity only.	1. Potential difference is voltage between any two points in a closed circuit.
2. EMF is measured when circuit is open.	2. P.d is measured when circuit is closed.
3. EMF doesn't depend upon the resistance of the circuit.	3. Potential difference depends upon the resistance of the circuit and is directly proportional to it. V   α  R
4. EMF is greater than the potential difference in the same circuit.	4. Potential difference is less than EMF in same circuit.