Resistance of a hot metal
I can explain why the resistance of a metal filament changes as the p.d. across it increases.
Resistance of a hot metal
I can explain why the resistance of a metal filament changes as the p.d. across it increases.
Lesson details
Key learning points
- As the p.d. across a filament lamp increases, it gets hotter and current through it increases in a non-ohmic way.
- The greater the p.d. across a filament lamp, the greater its resistance.
- A metal is made of a lattice of positively charged ions with negatively charged electrons between.
- As a current flows through metal, electrons moving through the ion lattice cause it to vibrate more vigorously.
- The more vigorously the ions (ion lattice) vibrate, the hotter the metal and the higher its resistance.
Common misconception
The gradient of an I-V graph is equal to 1/R because I = V ÷ R.
Explain how the equation for a straight line graph y = mx + c does not apply in this case because the graph is not a straight line.
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
Licence
This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).
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