Capacitance Capacitance occurs whenever electrical conductors are separated by a dielectric, or insulating material. Applying a voltage to the conductors can displace the charge within the dielectric. Current does not actually flow through the dielectric. ECE 201 Circuit Theory I

Capacitance Capacitor Structured as two parallel plates ECE 201 Circuit Theory I

Capacitor Circuit Symbol (a) Component designation (C) Units – Farads Usually μF or pF Reference directions for voltage and current (b) ECE 201 Circuit Theory I

Voltage-Current Relationship ECE 201 Circuit Theory I

Observations The voltage across a capacitor cannot change instantaneously (the current would be infinite). If the voltage across the terminals is constant, the current will be zero. (looks like an open circuit). Only a time-varying voltage can produce a displacement current. ECE 201 Circuit Theory I

Express the voltage across the capacitor as a function of the current ECE 201 Circuit Theory I

Power and Energy for the Capacitor ECE 201 Circuit Theory I

Example 6.4 A voltage pulse described as follows is applied across the terminals of a 0.5μF capacitor: ECE 201 Circuit Theory I

Derive the expressions for the capacitor current, power, and energy. ECE 201 Circuit Theory I

Power ECE 201 Circuit Theory I

Energy ECE 201 Circuit Theory I

Energy is being stored whenever the power is positive. Energy is being delivered by the capacitor whenever the power is negative. ECE 201 Circuit Theory I