Capacitors & Capacitance — A/L Physics

What must I remember about Capacitors & Capacitance?

• Capacitance Definition: Ability of a conductor or system of conductors to store electric charge per unit potential difference: C = Q / V (scalar quantity, units Farad = C/V).
• Parallel Plate Capacitor: Consisting of two parallel conducting plates of area A separated by distance d with dielectric medium ε_r: C = (ε_r ε0 A) / d; inserting dielectric increases capacitance by factor ε_r.
• Combinations of Capacitors: In Parallel: Equivalent capacitance C_eq = C1 + C2 + C3 (same voltage across each, charges add); In Series: 1 / C_eq = 1/C1 + 1/C2 + 1/C3 (same charge on each, voltages add).
• Energy Stored in a Charged Capacitor: U = (1/2) Q V = (1/2) C V² = Q² / (2C); stored in the electrostatic field between plates; Energy Density u_e = (1/2) ε0 E² (J/m³).

Test yourself (1 minute)

1. Dielectric insertion under Battery Connected vs Disconnected

   Battery Connected (V constant): C increases (×ε_r), Q increases (×ε_r), E remains constant (V/d), U increases (×ε_r); Battery Disconnected (Q constant): C increases (×ε_r), V drops (/ε_r), E drops (/ε_r), U decreases (/ε_r, mechanical work done by field pulling dielectric in).

2. Energy loss during capacitor sharing

   When charged capacitor C1 at V1 is connected to uncharged C2, common voltage V = (C1 V1)/(C1 + C2); Energy lost as heat/radiation: ΔU = (1/2) [ (C1 C2) / (C1 + C2) ] V1².

3. Dielectric Breakdown

   Maximum electric field a dielectric material can withstand without electrical discharge / sparking is its dielectric strength (Air ≈ 3 × 10⁶ V/m).

Practise Capacitors & Capacitance questions today

Source: NIE G.C.E. (A/L) Physics Resource Book - Unit 6: Electrostatic Field

What should I study first?

Next in the syllabus

Where does Capacitors & Capacitance fit in the syllabus?

Unit 6.5 · Year 1 · Term 3