1. Voltage and Current
Whenever positive and negative charges are separated,
Voltage is the energy per unit charge created by the separation.
Where v = the voltage in volts
w = the energy in joules
q = the charge in coulombs
ECE 201 Circuit Theory I

2. Voltage and Current (continued)
The rate of charge flow is electric current
Where i = the current in amperes
q = the charge in coulombs
t = the time in seconds
ECE 201 Circuit Theory I

3. Power and Energy
Power is the time rate of expending or absorbing energy.
Where p = the power in watts
w = the energy in joules
t = the time in seconds
1 Watt = 1 Joule/second
ECE 201 Circuit Theory I

4. Power Associated with the flow of charge
Using the definitions of Voltage and Current
Where p = the power in Watts
v = the voltage in volts
i = the current in amperes
ECE 201 Circuit Theory I

5. The Basic Ideal Circuit Element
The ideal basic circuit element
has only two terminals
is described mathematically in terms of current and/or voltage
Cannot be subdivided into other elements
ECE 201 Circuit Theory I

6. Passive Sign Convention
If the power is positive (p>0), power is being delivered to the circuit inside the box. If the power is negative (p<0), power is being extracted from the circuit inside the box.
ECE 201 Circuit Theory I

7. Circuit Theory What is an electric circuit?
A mathematical model that approximates the behavior of an actual electrical system.
Example: Automobile Headlights
Here the headlights are OFF and draw no current from the battery because the switch is open.
ECE 201 Circuit Theory I

8. Automobile Headlights (continued)
Turn the headlights ON by closing the switch.
The headlights are ON. They draw a current of Amperes from the battery.
ECE 201 Circuit Theory I

9. Jump Starting Example The current is measured to be 40 Amperes.
Which car has the dead battery?
ECE 201 Circuit Theory I

10. The current is flowing into the + terminal of the battery in car A.
p = vi = (12V)(40A) = 480W
Since the power is positive, the battery in car A is absorbing power. Car A has the dead battery.
ECE 201 Circuit Theory I

11. Additional Calculation
If this connection is maintained for 1.5 minutes, how much energy is transferred to the dead battery?
ECE 201 Circuit Theory I