Lesson 06
Review
Review the capacitor test and strengthen weak areas.
Objectives
Lesson outcomes
- Correct errors from the capacitor test using clear physics reasoning.
- Identify whether mistakes came from definitions, equation choice, graph interpretation, unit conversion, or exponential modelling.
- Set targeted follow-up practice for the weakest part of capacitance.
Syllabus
CIE 9702 syllabus points
7 linked
- 19.1.1 define capacitance, as applied to both isolated spherical conductors and to parallel plate capacitors
- 19.1.2 recall and use C = Q / V
- 19.2.1 determine the electric potential energy stored in a capacitor from the area under the potential–charge graph 1 1
- 19.2.2 recall and use W = 2 QV = 2 CV 2
- 19.3.1 analyse graphs of the variation with time of potential difference, charge and current for a capacitor discharging through a resistor
- 19.3.2 recall and use τ = RC for the time constant for a capacitor discharging through a resistor
- 19.3.3 use equations of the form x = x0 e –(t / RC) where x could represent current, charge or potential difference for a capacitor discharging through a resistor
Definitions
Required definitions
Capacitance
charge stored per unit potential difference.
Lesson Notes
Student guidance and lesson notes
Overview
This lesson uses the capacitor test to improve your next round of revision. The aim is to understand why errors happened, correct them properly, and decide what needs more practice.
What You Need to Know
- A useful correction explains the capacitor model, not just the final answer.
- Common weak points include unit prefixes, stored energy equations, discharge graph interpretation, and exponential decay equations.
- Capacitor questions often require a clear choice between charge, p.d., current, energy, and time constant models.
- Feedback should lead to a specific practice target.
How to Work Through It
- Sort your test errors by topic and skill: definitions, equations, graphs, units, or algebra.
- Rewrite selected answers with the missing physics included.
- Rework at least one similar question without looking at the original solution.
- Finish with a short target for future capacitor revision.
Check Your Understanding
- Which mistake cost the most marks, and why?
- Was the weak step physics understanding, equation choice, graph reading, units, or exam wording?
- Can you now explain the corrected answer without reading from the mark scheme?
Common Mistakes
- Copying the mark scheme without identifying the original misconception.
- Correcting calculations while leaving the wrong model choice unchanged.
- Treating one weak graph question as isolated when it shows a broader time-constant issue.
- Ignoring unit-conversion errors because the method looked familiar.
Next Steps
- Add the weakest capacitor subtopic to your next independent revision cycle.
- Keep corrected examples available for later circuit and field revision.