Transcript Potential Difference

Potential Difference
Electricity Lesson 2
Learning Objectives

To know what is meant by potential difference.

To define potential difference.

To define the emf of a source.

To calculate electrical power supplied to a
device.
Potential Difference

The work done per unit charge is defined as the
potential difference (pd) or voltage across the
component.

Potential difference is defined as the work
done (or energy transfer) per unit charge.

The unit of pd is the volt which is equal to 1
joule per coulomb.
Potential Difference

If work W is done when charge Q flows through
the component, the pd across the component V
is given by:-
W
V
Q

In words:-
work done
p.d. 
charge flow
Example 1

If 30 J of work is done when 5 C of charge
passes through a component, what is the pd
across it?
Example 1

If 30 J of work is done when 5 C of charge
passes through a component, what is the pd
across it?
W 30 J
V

6V
Q 5C
Example 2

If the pd across a component in a circuit is 12 V,
how much energy is transferred from the battery
to the component if 3 C of charge passes
through it?
Example 2

If the pd across a component in a circuit is 12 V,
how much energy is transferred from the battery
to the component if 3 C of charge passes
through it?
W  QV  3 C 12 V  36 J
The emf of a source

The emf of a source of electricity is defined
as the electrical energy produced per unit
charge passing through the source.

The unit of emf is the volt, the same as the unit
of pd.
For a source of emf, ε, in a circuit, the electrical
energy produced when charge Q passes through
the source = Qε  transferred to other parts of
the circuit.

Electrical Power
Q  It
W  QV  IVt

Consider a component

The symbol Δ is delta, a Greek capital letter Δ,
meaning “change in”.
power  current  p.d.
P  IV
Current

For a current I, the charge flow ΔQ in a time Δt
is given by:-
Q
I
t