Capacitance and Combinations
Capacitance C = Q/V measures charge stored per unit potential difference; a parallel-plate capacitor has C = e0 A/d and stores energy CV2/2.
What is Capacitance and Combinations?
Capacitance C = Q/V measures charge stored per unit potential difference; a parallel-plate capacitor has C = e0 A/d and stores energy CV2/2.
Key formula / rule: C = e0 A/d for a parallel-plate capacitor.
Key points
- Compute equivalent capacitance for networks.
- Analyse energy change when a capacitor is modified with the source connected or disconnected.
Common exam trap
Swapping the series and parallel rules with those of resistors.
Definitions
- Term
Capacitance and Combinations
- Meaning
Capacitance C = Q/V measures charge stored per unit potential difference; a parallel-plate capacitor has C = e0 A/d and stores energy CV2/2.
- Term
Capacitance and Combinations — explanation
- Meaning
Series and parallel combinations behave oppositely to resistors: capacitances add in parallel and reciprocals add in series.
Learning objectives
Compute equivalent capacitance for networks.
Analyse energy change when a capacitor is modified with the source connected or disconnected.
Formulae
- Key point
C = e0 A/d for a parallel-plate capacitor.
- Key point
Parallel: C = C1 + C2. Series: 1/C = 1/C1 + 1/C2.
- Key point
Energy stored U = CV2/2 = Q2/2C.
Prerequisites
PHY-U5-ELS-T2-S1-C1
Common mistakes
Swapping the series and parallel rules with those of resistors.
Assuming charge stays constant when the source remains connected.
Keywords
Capacitance
Combinations
Practice preview
The capacitance of a parallel plate capacitor with plate area A and separation d is given by C = e0 A/d. If the plate separation is doubled and the plate area is halved, what happens to the capacitance?…
easy
A 10 microF capacitor is charged to a potential difference of 200 V. What is the energy stored in the capacitor?…
medium
A parallel plate capacitor has capacitance C0. If a dielectric slab of dielectric constant k is inserted to completely fill the space between the plates, which of the following statements is INCORRECT?…
medium