# KS5 Capacitance

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# Capacitance Learning Objectives Content

• Definition of capacitance: C = Q V
• Dielectric action in a capacitor C = AƐ0Ɛr/d
• Relative permittivity and dielectric constant.
• Students should be able to describe the action of a simple polar molecule that rotates in the presence of an electric field.
• Interpretation of the area under a graph of charge against pd.
E = ½ QV = ½ CV2 = ½ Q2/C
• Graphical representation of charging and discharging of capacitors through resistors. Corresponding graphs for Q, V and I against time for charging and discharging.
• Interpretation of gradients and areas under graphs where appropriate.
• Time constant RC.
• Calculation of time constants including their determination from graphical data.
• Time to halve, T ½ = 0.69RC
• Quantitative treatment of capacitor discharge, Q = Q0e− t/RC
• Use of the corresponding equations for V and I.
• Quantitative treatment of capacitor charge, Q = Q0 (1 − e− t/RC) Back to Teaching Rota