Capacitors | OCR A-Level Physics A (H556)

Capacitors

93 questions
8 subtopics
Module 6: Particles and medical physics
Paper 2 and Paper 3

Storing charge and energy: capacitance, combining capacitors, the energy on a charged capacitor, and the exponential curve that governs charging and discharging..

It covers capacitance and charging a capacitor, capacitors in series, capacitors in parallel and combined circuits, energy stored by a capacitor, charging and discharging through a resistor, investigating capacitor discharge, the time constant and iterative modelling, exponential decay and the constant-ratio property.

Sample questions from Capacitors

Answer each one closed book first, then open the answer.

Capacitance and charging a capacitor

In the equation C = Q/V, what does each symbol represent?

Show the answer
C is capacitance (in farads), Q is charge stored (in coulombs), and V is potential difference across the capacitor (in volts).
Capacitors in series

What is true about the charge stored on capacitors connected in series?

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All capacitors in series store the same charge.
Capacitors in parallel and combined circuits

How is charge distributed among capacitors connected in parallel?

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The charge stored is shared between the capacitors.
Energy stored by a capacitor

In the equation W = ½QV, what does each symbol represent?

Show the answer
W is energy stored (in joules), Q is charge (in coulombs), and V is potential difference (in volts)
Charging and discharging through a resistor

At what point does a capacitor stop charging?

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Charging stops when the capacitor voltage equals the supply voltage.
Investigating capacitor discharge

How should readings be taken when manually investigating capacitor charge or discharge?

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Readings should be taken at regular time intervals during charge or discharge.
The time constant

Calculate the time constant when capacitance = 0.0086 F, resistance = 94000 Ω.

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Time constant = 0.0086 × 94000 = 808 s.
Iterative modelling, exponential decay and the constant-ratio property

Why is taking natural logarithms of the discharge equation useful for data analysis?

Show the answer
It transforms the exponential relationship into a linear relationship with time t.

The 8 subtopics

One subtopic is one session. Work down the list.

Subtopic	What it covers	Questions
Capacitance and charging a capacitor	Recall questions on capacitance, the farad and C = Q/V with calculations, and how electrons move onto and off the plates when a capacitor charges and discharges.	14
Capacitors in series	Recall questions on total capacitance in series and calculations, charge and potential difference across series capacitors, and investigating capacitors in series with voltmeters and an ammeter.	10
Capacitors in parallel and combined circuits	Recall questions on total capacitance in parallel and calculations, potential difference and charge for parallel capacitors, Kirchhoff's laws in capacitor circuits, and investigating capacitors in parallel.	10
Energy stored by a capacitor	Recall questions on the p.d.-charge graph, the three expressions for stored energy, and uses of capacitors as energy stores.	18
Charging and discharging through a resistor	Recall questions on how charge, potential difference and current change as a capacitor charges and discharges through a resistor, the charging equation, and the ln(x) against t graph.	14
Investigating capacitor discharge	Recall questions on investigating capacitor discharge manually with a voltmeter and stopwatch or with a data-logger, and the linearised logarithmic form of the discharge equation.	8
The time constant	Recall questions on the time constant CR with calculations, the fractions reached after one time constant during charging and discharging, the exponential discharge equation, and finding CR from a ln(x) against t graph.	8
Iterative modelling, exponential decay and the constant-ratio property	Recall questions on the iterative equation ΔQ/Δt = −Q/CR, modelling capacitor discharge on a spreadsheet, why logarithms help analysis, and the shape and constant-ratio property of exponential decay.	11

Capacitors is 93 of the 1,862 questions in the guide.Get the guide, £8

How the guide is worked

Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.

Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.

Read the full method, the return schedule and the research behind it.