Key point

The resistance of a metallic conductor at constant temperature depends on:

  • The length l. Resistance is directly proportional to length.

An electric current flows when free electrons move in one direction through a conductor, such as a metal wire.

The moving electrons can collide with the ions in the metal.

This makes it more difficult for the current to flow, and causes resistance.

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.

Resistance and wire length are directly proportional.

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