- As electrons pass through a wire, they collide with the metal ions in the wire
Electrons collide with ions, which resist their flow
- The ions get in the way of the electrons, resisting their flow
- If the wire is longer, each electron will collide with more ions and so there will be more resistance:
The longer a wire, the greater its resistance
- If the wire is thicker (greater diameter) there is more space for the electrons and so more electrons can flow:
The thicker a wire, the smaller its resistance
The length and width of the wire affect the resistance
- The resistance of a wire is proportional to its length
- This means that if the length of a wire is doubled, its resistance will double
- The resistance of a wire is inversely proportional to its cross-sectional area
- This means that is the cross-sectional area of a wire is doubled, its resistance will halve
Cross-sectional area is proportional to the diameter squared.
This means that if the diameter is doubled, the cross-sectional area will quadruple, causing the resistance to drop to a quarter.