Grade 9 Electricity Practice Exam

What is electric potential difference and its unit?

The rate at which electrical energy is supplied by a source; unit is the watt. The energy stored per unit charge between two points in a circuit; unit is the volt (V). The energy difference per unit charge between two points in a circuit. The opposition to current flow in a circuit; unit is the ohm.

Correct Answer:

The energy difference per unit charge between two points in a circuit.

Explanation:

Electric potential difference, or voltage, is about how much energy per unit charge is gained or lost as charges move between two points in a circuit. The unit is the volt, and one volt equals one joule per coulomb (1 V = 1 J/C). In simple terms, if a charge of q coulombs moves through a potential difference of ΔV, the energy change is ΔE = qΔV. So moving 1 coulomb through 1 volt gives 1 joule of energy. This is why a battery or power source with a higher potential difference can push charges to do more work as they flow through the circuit. The other ideas—power (rate of energy transfer, measured in watts), opposition to current (resistance in ohms), or energy stored per unit charge—don’t define what the potential difference itself measures.

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