Potential difference

Potential difference

A ball held off the ground has potential.

Its potential is, it could fall and hit the

ground.

Similarly, a cell or battery with

positive and negative plates has the

potential to cause electron drift.

The force which pushes electrons along a

conductor is an emf.

We use a battery or generator to produce an emf.

The emf is measured by the

number of joules of work needed to push one coulomb of electrons along a circuit.

It is measured with the unit joules per coulomb.

It is better known as the volt.

We can say that:

one volt = one joule/coulomb.

Note

When a coulomb of electrons leaves a battery

or generator it has a potential energy

measured in joules. As it travels

around the circuit the energy is used up, so

when it arrives back at the battery it has

no energy at all.

Electromotive force (e)= E (energy in joules,J)

Q (charge in coulombs,C)

The amount of energy that a coulomb uses

as it goes between any two points in a

circuit is known as the potential

difference. It is measured in

joules/coulomb or volts.

To understand this, think of a marathon

runner. At the start of the race they are

fresh and full of energy. But as the race

goes on they use up energy until at the

end they have no energy left.

So at the start they have the energy

(potential) to run the race. At the end

they no longer have the ability (potential) to

run a race. They have used up all their

energy.

The gap between the two is the potential

difference.

We can say that a current couldn’t exist

without a potential difference.

Magnetic effect of current

When current flows, heat is produced.

It also creates a magnetic effect.

When a conductor carries current around

a circuit, a magnetic field will be produced

around the conductor.

When current passes through a wire a small magnetic field is produced. The direction of

the “flux” lines or magnetic field lines is dependent on current.