Resistance in a wire

Resistance in a wire is caused by the positive metal ions in the metal blocking the flow of electrons.

The type of material determines the resistance (but so do other things like the length and thickness of the wire).

Resistance is inversely proportional to the current (if the potential difference is constant). This means that as resistance increases, current decreases.

Resistance is directly proportional to the potential difference (if the current is constant). This means that as resistance increases, potential difference increases.

Factors affecting resistance

• Area of cross-section (thickness)
  • Thicker wires have less resistance
  • That’s because there is more space for the electrons to flow through without colliding with the metal ions
• Length of wire
  • Longer wires have more resistance
• Temperature
  • Higher temperatures increase resistance
  • That’s because, at higher temperatures, the metal ions vibrate more so collide with the electrons more frequently
• Material
  • Some materials have more resistance than others
  • This is called the material’s resistivity