Potential Difference

1
Potential Difference

• Electricity Lesson 2

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.

3
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.

4
Potential Difference

• If work W is done when charge Q flows through the
  component, the pd across the component V is given
  by-
• In words-

5
Example 1

• If 30 J of work is done when 5 C of charge passes
  through a component, what is the pd across it?

6
Example 1

• If 30 J of work is done when 5 C of charge passes
  through a component, what is the pd across it?

7
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?

8
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?

9
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, e, in a circuit, the
  electrical energy produced when charge Q passes
  through the source Qe ? transferred to other
  parts of the circuit.

10
Electrical Power

• Consider a component
• The symbol ? is delta, a Greek capital letter ?,
  meaning change in.

11
Current

• For a current I, the charge flow ?Q in a time ?t
  is given by-