L4 - Potential Difference

objectives

Potential Difference

• The cell above is pushing out electrons.
• The electrons repel each other, so, like the coils of a compressed spring, they have potential energy.
• As the electrons slowly flow round the circuit, they transfer energy from the cell to the lamp.
• The energy is radiated by the hot filament.

Potential Difference Across a Circuit

• A cell normally has a voltage marked on it.
• The higher its voltage, the more energy it gives to the electrons pushed out.
• he scientific name for voltage is potential difference (p.d.).
• P.d. can be measured by connecting a voltmeter across the terminals of the cell.

Cells in Series

• To produce a higher p.d., several cells can be connected in series (in line) as shown below.
• The word ‘battery’ really means a collection of joined cells, although it is commonly used for a single cell as well.

Potential Difference Across a Circuit

• Like the battery, each lamp has a p.d. across it:
  • If a lamp (or other component) has a p.d. of 1 volt across it, then 1 joule of potential energy is spent by each coloumb of charge passing through it.
  • The second diagram shows the same circuit with voltmeters connected across different sections (the voltmeters do not affect how the circuit works). The readings illustrate a principle which applies in any circuit: