1. ECE 201 Circuit Theory I1 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.

2. ECE 201 Circuit Theory I2 Capacitance Capacitor –Structured as two parallel plates

3. ECE 201 Circuit Theory I3 Capacitor Circuit Symbol (a) Component designation (C) Units – Farads –Usually μF or pF Reference directions for voltage and current (b)

4. ECE 201 Circuit Theory I4 Voltage-Current Relationship

5. ECE 201 Circuit Theory I5 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.

6. ECE 201 Circuit Theory I6 Express the voltage across the capacitor as a function of the current

7. ECE 201 Circuit Theory I7 Power and Energy for the Capacitor

8. ECE 201 Circuit Theory I8 Example 6.4 A voltage pulse described as follows is applied across the terminals of a 0.5μF capacitor:

9. ECE 201 Circuit Theory I9 Derive the expressions for the capacitor current, power, and energy.

10. ECE 201 Circuit Theory I10 Power

11. ECE 201 Circuit Theory I11 Energy

12. ECE 201 Circuit Theory I12 Energy is being stored whenever the power is positive. Energy is being delivered by the capacitor whenever the power is negative.