Electric Circuits

1
Electric Circuits
2
Power Sources

• Power supplies provide both voltage and current.
• Direct Current (DC)
• Batteries and AC adapters
• Alternating Current (AC)
• Current follows a sine wave.
• Ex. Wall outlet

3
Battery

• A source of electric potential due to a chemical
  reaction.

At the Anode
At the Cathode
4
Power Supply

• Any source of electrical power.
• It supplies both voltage and current

e - Electromotive force r - Internal resistance R
- Load resistance
e
R
r
Power Supply
5
Voltage to Load

• The voltage supplied to a load is given by
• Ex. What is the voltage supplied by a 9 volt
  battery, which has an internal resistance of 15
  W, when a circuit is drawing 250 mA of current?

6
Resistor Combos

• Series - The same current goes through each of
  the resistors.
• Parallel - The same voltage is applied across
  each of the resistors.

7
Kirchoffs Rules

• Sum of the currents entering a junction equals
  the sum of the currents leaving a junction.
• Sum of the changes in potential across all the
  elements in a closed loop is zero.

8
Loop Traversal

• Voltage across a resistor
• Across a resistor with the current, -IR
• Across a resistor against the current, IR
• Voltage across a power source
• Across an emf source from - to , e
• Across an emf source from to -, -e

9
Network Circuit
Node Equation
Loop Equation
10
Bridge Circuit
11
RC Circuits

• At t 0s close a switch on an RC circuit with an
  uncharged capacitor.

Max. Current
Max. Charge
12
Time Constant

• Charging Capacitor
• Time Constant, t

• Ex. What is the time constant for an RC circuit
  with R1.0kW and C500mF?

13
Discharging Capacitor

• At t 0s the capacitor is discharged through
  resistor R.