Capacitors and Capacitance

Overview

Introduce capacitance and capacitor combinations in series and parallel. You will define capacitance, use C = Q / V, and then apply the same charge and p.d. ideas to capacitor networks.

What You Need to Know

• Apply capacitance to isolated spherical conductors and parallel plate capacitors.
• Use C = Q / V to connect charge, capacitance, and potential difference.
• A larger capacitance means more charge is stored for the same potential difference.
• For capacitors in parallel, the p.d. across each capacitor is the same and the total charge is shared between branches.
• For capacitors in series, the charge on each capacitor is the same and the total p.d. is shared across the capacitors.
• Use the combined capacitance formulae for capacitors in series and in parallel.
• The farad is a large unit, so practical values are often given in microfarads or nanofarads.
• Charge must be in coulombs and p.d. in volts when using SI units.

How to Work Through It

1. Start by recalling charge, potential difference, and energy transfer in circuits.
2. Define capacitance and link it to the capacitor symbol and physical storage of charge.
3. Practise rearranging C = Q / V with unit conversions.
4. Compare series and parallel capacitor networks by tracking charge and p.d.
5. Calculate combined capacitance and check whether the answer is sensible.

Check Your Understanding

• What does capacitance measure?
• Why does a capacitor with larger capacitance store more charge at the same p.d.?
• What charge is stored on a 220 microfarad capacitor at 6.0 V?
• What stays the same for capacitors in series, and what stays the same for capacitors in parallel?

Common Mistakes

• Treating capacitance as the charge stored rather than charge per unit p.d.
• Forgetting to convert microfarads or nanofarads into farads.
• Confusing charge on one plate with current in the circuit.
• Mixing up the series and parallel capacitor rules by copying resistor rules.

Next Steps

• Keep C = Q / V secure before using capacitor energy equations.
• Keep the network rules available for later circuit comparison questions.
• Bring graph-area ideas into the next lesson on stored energy.