1. 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

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

3. 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

4. Voltage-Current Relationship
ECE 201 Circuit Theory I

5. 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

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

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

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

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

10. Power
ECE 201 Circuit Theory I

11. Energy
ECE 201 Circuit Theory I

12. 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