Physics 10.25 - Reducing unwanted wire heating

Reducing unwanted transfer in wires

Connecting wires should carry current without becoming deliberate heaters. A wire with
lower resistance transfers less electrical energy into thermal energy while carrying the
required current, so less energy is dissipated in the wire and its temperature rises less.

Resistance can be reduced by changing the wire:

• Use a low-resistivity material. Copper is commonly used because it offers little
  electrical resistance for a practical metal wire.
• Make the wire thicker. A larger cross-sectional area gives more conducting paths for
  the mobile electrons, reducing the resistance.
• Avoid unnecessary length. A shorter wire gives electrons a shorter resistive path,
  reducing the resistance.

The design choice depends on purpose. A heating element needs a substantial heating effect;
the connecting wires that supply it should have low resistance so that the useful transfer
is concentrated in the element rather than the leads.

Choose a design for its purpose

The comparison must specify the operating condition. Here the wire must carry the same required current. Lower wire resistance then means less energy transferred into the wire each second. If a wire alone were connected directly across a fixed-voltage supply, reducing its resistance would also increase the current; that is a different comparison.