Revision as of 10:35, 22 October 2009

PH5.1 CAPACITANCE

Content

• The parallel plate capacitor.
• Concept of capacitance.
• Factors affecting capacitance.
• Energy stored in a capacitor.
• Capacitors in series and parallel.
• Capacitor discharge.

AMPLIFICATION OF CONTENT Candidates should be able to:

5.1 (a) understand that a simple parallel plate capacitor consists of a pair of equal parallel metal plates separated by vacuum or air,

5.1 (b) understand that the capacitor stores energy by transferring charge from one plate to the other, so that the plates carry equal but opposite charges (the net charge being zero),

5.1 (c) define capacitance as C=Q/V,

5.1 (d) use C=εoA/d for a parallel plate capacitor, with no dielectric,

5.1 (e) know that a dielectric increases the capacitance of a vacuum-spaced capacitor;

5.1 (f) recall that the E field within a parallel plate capacitor is uniform and of value V/d,

5.1 (g) use the equation U=1/2QV for the energy stored in a capacitor,

5.1 (h) use formulae for capacitors in series and in parallel,

5.1 (i) understand the process by which a capacitor discharges through a resistor,

5.1 (j) use the equation Q=Q0e−t/RC where RC is the time constant.