How does potential difference represent energy per unit charge?
Potential difference represents energy per unit charge because it measures how much energy an electric field gives to each coulomb of charge as it moves through a circuit. When a battery or power source creates a potential difference, it establishes different electric potentials at its terminals. A charge moving from the negative terminal to the positive terminal experiences a change in electric potential, and this change corresponds directly to the energy transferred. If the potential difference is large, each unit of charge gains or loses more energy. This is why voltage is often described as the “push” behind electric current—it quantifies how strongly the electric field influences charge.
Microscopically, potential difference is the result of work done by the power supply. A battery uses chemical energy to separate charges: it moves electrons toward one terminal and away from the other. This separation creates an imbalance, forming an electric field. When a circuit is completed, the electric field does work on electrons, giving them energy as they drift through the conductor. The amount of work done per electron—or more precisely, per coulomb of charge—is the potential difference. It is a measure of how much energy is available to be converted into other forms, such as light, heat or motion.
This idea becomes clearer when considering energy transformations. If a device is connected across a 9-volt battery, each coulomb of charge moving through that device receives 9 joules of energy. The device then converts that energy into heat, mechanical work or electromagnetic radiation. The potential difference determines how much energy each charge delivers to the components it passes through. Higher voltage means more energy transferred per charge, leading to brighter bulbs, stronger motors or more powerful heating.
Potential difference is therefore not about the amount of charge flowing, but about the energy carried by each charge. Current describes how many charges flow each second, while voltage describes how much energy each of those charges carries. The combination of the two determines how much total energy moves through a circuit.
Frequently Asked Questions
Why isn’t voltage the same as current?
Voltage measures energy per charge, while current measures the rate of charge flow. A system can have high voltage but low current, or vice versa, depending on resistance and circuit design.
Why does a higher voltage make bulbs brighter?
Because each charge delivers more energy to the bulb. More energy per charge means more heating and more light output.
Can potential difference exist without current?
Yes. A battery with an open circuit still has voltage; it simply cannot transfer energy until charges are allowed to flow.
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