Electromotive force and potential difference Flashcards – Cambridge IGCSE (9–1) Physics 0972 (Extended) (2026–2028)

What is electromotive force (e.m.f.)?

The electrical work done by a source per unit charge in moving charge around a complete circuit.

What is the equation for e.m.f. in terms of work done by the source $W$ and charge moved $Q$?

$\mathcal{E} = \frac{W}{Q}$

What is the unit of e.m.f., and how is it expressed in joules per coulomb?

The volt (V): $1\,\mathrm{V} = 1\,\mathrm{J/C}$.

How is potential difference between two points defined, and what is its equation?

It is the work done per unit charge passing between the points: $V = W/Q$, where $W$ is work done and $Q$ is charge.

What is the unit of potential difference, and how is it related to the joule and coulomb?

The volt (V); one volt equals one joule per coulomb.

What does a voltmeter measure?

The potential difference between two points.

How is a voltmeter connected to measure the potential difference across a component?

Across the component, in parallel with it.

How do analogue and digital voltmeters indicate a reading?

An analogue voltmeter uses a pointer on a scale; a digital voltmeter displays a number.

What must be taken into account when reading an analogue voltmeter's scale?

The selected range.

What condition must a suitable voltmeter range satisfy?

It must include the expected voltage.

How should you select a voltmeter range when the voltage is unknown?

Start with a high range, then select a lower suitable range for a clearer reading.

How should a voltmeter's connections be arranged for a direct-current measurement?

Match the meter's positive and negative connections to the circuit polarity.

What reading results from reversing a digital voltmeter's connections in a direct-current circuit?

A negative reading.