Edexcel A-Level Physics Electric Current

Practise Edexcel A-Level Physics electric current with charge flow, electron counts, average current and circuit calculations.

Exam points

calculate circuit current from total electron charge using Q = Ne and I = Q/t
use circuit resistance and p.d. to find current before converting charge into electron number
determine average current from charge or changing-current data over a time interval

[Maximum number: 3]

The circuit contains three identical resistors and switches X and Y. Each resistor is wire of diameter $0.181\,\mathrm{mm}$ and length $55.0\,\mathrm{cm}$ , with resistivity $1.10\times10^{-6}\,\Omega\,\mathrm{m}$ at room temperature.

Figure for Question 2.4.64 - Electric current question 1 — Edexcel A-Level Physics AS

Switch X was open and switch Y was closed.

Calculate the number of conduction electrons passing through the resistor each second immediately after switch Y is closed.

Number of electrons =

Immediately after closing Y, $I=V/R=12.0/23.5=0.511\,\mathrm{A}$ . In one second $Q=It=0.511\,\mathrm{C}$ , so
$N=Q/e=0.511/(1.60\times10^{-19})=3.2\times10^{18}.$

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2.4.64 - Electric current question 1