Key learning points

1. As the p.d. across a filament lamp increases, it gets hotter and current through it increases in a non-ohmic way.
2. The greater the p.d. across a filament lamp, the greater its resistance.
3. A metal is made of a lattice of positively charged ions with negatively charged electrons between.
4. As a current flows through metal, electrons moving through the ion lattice cause it to vibrate more vigorously.
5. The more vigorously the ions (ion lattice) vibrate, the hotter the metal and the higher its resistance.

Keywords

• Filament lamp - a type of lamp that uses a hot wire to emit light

• Ohmic conductor - a conductor for which the current is directly proportional to the p.d.

• Directly proportional - a relationship between variables in which one is a multiple of the other

• Metal ion - a metal atom that has lost one or more outer electrons and has become positively charged

• Free electron - an electron from the outer shell of an atom that is free to move from ion to ion through a metal

Common misconception