Resistivity of wires and LDR circuits
Watch the whole lecture free
Make a free account to watch every lecture to the end: 3 practice questions, 4 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
That was the teaching part. The rest of this lecture is free with an account: 3 practice questions, 4 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
No password needed now: we email you a link to set one. Already have an account? Sign in, then come back to this page.
The teaching part (1 min) is free to watch. A free account opens the whole lecture: 3 practice questions, 4 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- A wire that keeps stretching
- Definitions first
Read the transcript of the teaching part
Last time
Before we start: last time, in Resistivity and temperature, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
A wire that keeps stretching
Pull a metal wire, and it gets longer. It also gets thinner, because the metal has to go somewhere. Both changes raise the resistance. So the resistance rises faster than the length, and we can prove exactly how fast.
Definitions first
The ohm is the resistance of a component when a potential difference of one volt gives a current of one ampere: volt per ampere. Potential difference is the energy transferred from electrical to other forms per unit charge. Resistance is the potential difference across the component per unit current in it: R equals V over I. These three definitions appear in the first part of many long questions. Learn them word for word.
Chapter 9.4: Resistance and resistivity
- Resistivity and temperature 6 min
- Resistivity of wires and LDR circuits 6 min
- Resistivity, drift speed and charge carriers 7 min
Also for A Level Physics 9702
Which topics come up most in A Level Physics 9702 past papers, counted from every paper since 2004: Paper 1 topic frequency, Paper 2 topic frequency.