resistance

• The resistance in a wire increases as:

  • the length of the wire increases
  • the thickness of the wire decreases
• The resistance of a long wire is greater than the resistance of a short wire because electrons collide with more ions as they pass through. The relationship between resistance and wire length is proportional.
• The resistance of a thin wire is greater than the resistance of a thick wire because a thin wire has fewer electrons to carry the current. The relationship between resistance and the area of the cross section of a wire is inversely proportional.
• voltage = current x resistance
• The filament in the bulb becomes hotter as the potential difference across it is increased, which increases the resistance of the filament.
• A diode only starts to allow current through it at voltages above about 0.6V and it only allows current to flow through it in one direction