Resistivity, drift speed and charge carriers
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 1 worked example, 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
- One wire, many questions
- The toolkit
Read the transcript of the teaching part
Last time
Before we start: last time, in Charge, current and drift speed, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
One wire, many questions
A single wire in a circuit lets an examiner ask a whole chain of questions. Find the current. Find the resistivity. Find the drift speed. Find how many charge carriers there are. The same four equations connect everything, and this lesson ties them together.
The toolkit
Ohm's law form of resistance: R equals V over I. Resistivity: R equals rho L over A, so rho equals R A over L. Charge: Q equals I t. Drift speed: I equals n A v q, with q equal to e for electrons. Always convert to metres, seconds and coulombs first, and keep track of significant figures.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Drift speed.
The whole chapter: Electricity, Electricity.
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.