# Electromotive Force

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Electromotive Force (e.m.f.) of a source is the energy converted from non-electrical to electrical form when one coulomb of positive charge passes through the source.

• SI unit: Volt (V)

$E = \frac{W}{Q}$, where E = e.m.f., W = work done by source, Q = amount of positive charges

Potential difference between two points is defined as the energy converted from electrical to other forms when a coulomb of positive charge passes between the two points.

• SI unit: Volt (V)

$V = \frac{W}{Q}$, where V = potential difference, W = work done in driving the charge between the two points, Q = amount of positive charges

IMPORTANT: There can be e.m.f. without a closed circuit. BUT there cannot be a potential difference without a closed circuit.

Analogy to waterfalls:

In order to help you understand the concept of potential difference better, you can think of a waterfall. In the case of a waterfall, the water flows due to a height difference. In electric circuits, current flows between two points due to the existence of potential difference between the two points. No potential difference = no current. 