# Potential Difference

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When a torch bulb is connected to a battery, the torch bulb gets lit. The battery converts chemical energy into electrical energy and is therefore a source of electrical energy. The torch bulb converts electrical energy into heat and light and is therefore a sink of electrical energy.

• Dissipation of electrical energy between two points (e.g. across torch bulb) in an electrical circuit causes potential difference (p.d.) between those two points.
The potential difference (p.d.) between two points in a closed circuit is defined as the energy converted from electrical to other forms when a unit positive charge passes between the two points.
• SI unit of p.d. is the volt (V). It is the same as that of e.m.f.. (Both are measures of electrical potential energy, e.m.f. is gained electrical energy while potential difference is lost electrical energy.)
• $V = \frac{W}{Q}$