Edexcel A-Level Physics Capacitance

Practise Edexcel A-Level Physics capacitance by calculating stored charge, interpreting capacitor combinations and using farad units.

Exam points

use Q equals CV to calculate charge, capacitance or potential difference for capacitors
compare charge stored when capacitors are placed in parallel or series arrangements
determine capacitance from discharge-graph data using the RC time constant

[Maximum number: 3]

A student built the circuit shown. The capacitor was initially uncharged.

Figure for Question 4.4.100 - Capacitance question 1 — Edexcel A-Level Physics A2

She closed the switch and plotted a graph of current on ammeter $\mathrm{A}_{1}$ against time.

Determine the capacitance of the capacitor.

Capacitance =

Use $I=I_0e^{-t/(RC)}$ with two corresponding graph values, or use the time constant $\tau=RC$ . For example, $0.04=0.15e^{-10/(33\,000C)}$ , giving $C=2.27\times10^{-4}\,\mathrm{F}$ . Accept $2.0\times10^{-4}$ to $2.3\times10^{-4}\,\mathrm{F}$ .

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4.4.100 - Capacitance question 1