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Give a reason for each choice. Copper is used for the wires of a house…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Give a reason for each choice.
- Copper is used for the wires of a house.
- Manganin, an alloy, is used for standard resistors in laboratories.
- Aluminium is used for overhead power lines.
- Plastic covers the wires.
Need a reminder? The key ideaShow
: the resistance grows with the length, falls with the area, and depends on the material through its resistivity (in ). Change square millimetres to square metres: .
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) Copper has a very low resistivity, so little energy is wasted as heat.
Step 2. (b) Manganin's resistivity hardly changes with temperature, so the resistor keeps its value.
Step 3. (c) Aluminium has a low resistivity and is light, so long lines are cheaper to hang.
Step 4. (d) Plastic is an insulator, so the wires cannot be touched or short each other.
Answer: low resistivity; steady resistivity; low resistivity and light; an insulator.
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