1. ECE 201 Circuit Theory I1 Voltage and Current Whenever positive and negative charges are separated, –Voltage is the energy per unit charge created by the separation. Wherev = the voltage in volts w = the energy in joules q = the charge in coulombs

2. ECE 201 Circuit Theory I2 Voltage and Current (continued) The rate of charge flow is electric current Wherei = the current in amperes q = the charge in coulombs t = the time in seconds

3. ECE 201 Circuit Theory I3 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

4. ECE 201 Circuit Theory I4 Power Associated with the flow of charge Using the definitions of Voltage and Current Wherep = the power in Watts v = the voltage in volts i = the current in amperes

5. ECE 201 Circuit Theory I5 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

6. ECE 201 Circuit Theory I6 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.

7. ECE 201 Circuit Theory I7 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.

8. ECE 201 Circuit Theory I8 Automobile Headlights (continued) –Turn the headlights ON by closing the switch. The headlights are ON. They draw a current of 4.138 Amperes from the battery.

9. ECE 201 Circuit Theory I9 Jump Starting Example Problem #1.15 The current is measured to be 30 Amperes. Which car has the dead battery?

10. ECE 201 Circuit Theory I10 The current is flowing into the + terminal of the battery in car A. p = vi = (12V)(30A) = 360W Since the power is positive, the battery in car A is absorbing power. Car A has the dead battery.

11. ECE 201 Circuit Theory I11 Problem # 1.15 part (b) If this connection is maintained for 1minute, how much energy is transferred to the dead battery?