I found that when I searched for information on this on the internet there was too much information in most articles and videos - for example many of them mention resistivity which we haven't covered yet.
The title of this post tells you the answer to how - the resistance of metals increases with increasing temperature. To explain why the resistance changes needs you to get a picture of what is going on inside the wire, and why the wire resists the flow of electrons in the first place.
N.B. I'd originally told you to type this up but I'd prefer you to write it by hand, with hand-drawn diagrams. You need to explain:
- why metals have resistance to the flow of electrons
- why the resistance increases when the temperature of the metal increases.
Extracts from an old science film.
I also found some extracts from a very old (1945) American film called 'Principles of Electricity' that might help - read my comments and watch these three short extracts linked below.
The first extract is a reminder of what electric current actually is. The narrator uses the term 'pressure' for potential difference or voltage - this makes sense, as it the the potential difference which 'pushes' the current through a circuit, but it is not a term that we use in A level physics in the UK.
N.B. At about 40 seconds he makes a mistake when he says that "the current is the number of electrons that pass a given point in a given time" when it should have said "the current depends the number of electrons that pass a given point in a given time"
This second extract explains the difference between insulators and conductors, and how collisions with the lattice of atoms causes resistance in metals and why a resistor gets hot when a current flows through it:
I also found some extracts from a very old (1945) American film called 'Principles of Electricity' that might help - read my comments and watch these three short extracts linked below.
The first extract is a reminder of what electric current actually is. The narrator uses the term 'pressure' for potential difference or voltage - this makes sense, as it the the potential difference which 'pushes' the current through a circuit, but it is not a term that we use in A level physics in the UK.
N.B. At about 40 seconds he makes a mistake when he says that "the current is the number of electrons that pass a given point in a given time" when it should have said "the current depends the number of electrons that pass a given point in a given time"
This second extract explains the difference between insulators and conductors, and how collisions with the lattice of atoms causes resistance in metals and why a resistor gets hot when a current flows through it:
This third section should improve your understanding of resistance in metals - it's to do with how often the conduction electrons collide with the metal atoms.
The first 2 minutes and 25 seconds of this video are useful (after this it goes into some equations that are no longer included in the A level physics specification - so don't watch the rest!).
This video shows balls (the electrons) moving through a lattice of rods (the atoms in the wire). You can see how the collisions with the rods (atoms) takes energy from the balls (electrons) and resists their movement through the model (the wire). I think you can also image that if the rods vibrated about at random then the balls would collide with them more often, increasing the resistance.
The first section of this webpage might also help you.
However I found that the best illustration is by using the Phet java simulation of a Battery-resistor circuit (download from here and try it yourself).
I recorded myself using it and added an explanation - see my video below.
Extension: we'll soon have to explain why the resistance of a thermistor decreases with increasing temperature - so get an early idea of this here.
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