Transcript Internal Resistance (def’n)

Electricity
Review of Year 12
Year 13 Material
Internal Resistance
Electrostatic Forces and Coulomb’s
Law

Like charges are
repelled from one
another, and unlike
charges are attracted.

The forces involved in
this repulsion/
attraction are given by
Coulomb’s law:
Electric Current

The electric force can be used to push
charge (measured in coulombs) around a
circuit.

A large positive charge is maintained at
one terminal of the battery, and a large
negative charge at the other terminal –
when they are linked by a circuit, charge
flows towards the negative terminal.

This results in electric current.
Energy and Potential Difference
For current to be maintained, the
difference in charge between the terminals
needs to be maintained.
 This means energy must be continuously
added to the system.
 The energy source (battery, power pack,
wall-socket) provides a potential
difference – this is the energy that it gives
to one coulomb of charge.

Internal Resistance (def’n)

Internal resistance
refers to the
resistance of a
voltage source
when a current is
flowing.

This results in a
lowered terminal
voltage.
Internal Resistance:


A battery in a circuit can be
regarded as a source of EMF
(electromotive force), ε, and a
resistor in series.
If we measure the voltage, V, across
the terminals of a battery in a
circuit, we are therefore measuring:
V = ε – Ir
V is the terminal voltage,
ε is the EMF
I is the current flowing
r is the internal resistance
ε
r
Practical Activity: Internal Resistance