1. Electrical Systems

2. Types of Circuits
Series Circuit: a circuit where current only follows only one path
Parallel Circuit: a circuit where current “branches off” in different directions

3. Types of Circuits
Short Circuit: a circuit made with a parallel branch using only a wire

4. Series & Parallel Circuits
Series Circuit
Current is the same at all points
All voltage drops add up to voltage of battery
Total resistance increases with more resistors
Parallel Circuit
All currents add up to the total current of battery
Voltage is the same at all points
Total resistance decreases with more resistors

5. Series Circuit Series Circuit: current can only follow one path.
All voltage drops add up to the voltage of the battery.
The current in a series circuit is the same at any point.
The total resistance increases as more resistors are added. R I V
1 Ω
0.25 A
0.25 V
2 Ω
0.50 V
3 Ω
0.75 V
Total = 6 Ω
Total = 0.25 A
Total = 1.5 V

6. R I V
Total =

7. R I V
Total =

8. R I V
Total =

9. Parallel Circuits
Parallel Circuits: a circuit where current ‘branches off’ in different directions.
All voltage drops are the same
The current across each load adds up to the current supplied by the battery.
Resistance decreases as more resistors are added. R I V
1 Ω
3 A
3 V
2 Ω
1.5 A
3 Ω
1 A
Total = 6/11 Ω
Total = A
Total = 3 V

10. R I V
Total =

11. R I V
Total =

12. R I V
Total =

13. Combination Circuits A combination of series and parallel.
Simplify resistors just in series or just in parallel
Redraw simplified circuits until there is a single resistor

14. Determine the total resistance

15. Find the Total Resistance

16. Find the Total Resistance

17. Find the Total Resistance

18. Short Circuits
Short Circuit (Short): a circuit made with a parallel branch using only a wire
Bypasses a part of the circuit
Increases the current through a circuit (less resistance)
Electricity always follows the path of least resistance.
Short circuits in homes can
Waste energy
Heat wires (melt the insulation or cause fires)

19. Which circuit below has a short in it?

20. Fuses A fuse prevents too much current from flowing through a circuit
It “breaks” if the current is too high.

21. What Is Power?

22. Power
Power: the amount of energy (work done) each second by a circuit.
Measured in watts

23. Determine the amount of power the circuit below has.

24. How much current flows through a 70 watt guitar amp that runs on a voltage of 120 volts?

25. Additional Problems
Determine the power used by a hair dryer that draws a current of 8 amps and runs on 120 volts of electricity.
Determine the current used by an iPod that runs on a 3.7 V battery and has a power of 2 watts.
Convert 200 cV to kV
Convert 4.5 in/min to m/hr

26. Electrical Power at Home
Electric meters measure kilowatt hours (kW·hr)
A 1 kW appliance ran for 1 hour = 1 kW·hr
Energy = P·t

27. An electric stove uses 3,000 watts of power
An electric stove uses 3,000 watts of power. It is used to bake for 30 minutes.
How many kilowatts of power does it use?
How many kilowatt hours does it use while baking?
If electricity costs $0.15 per kilowatt hour, how much does this cost?

28. A 100 watts light bulb is left on for 5.5 hours.
How many kilowatts of power does it use?
How many kilowatt hours does it use?
If electricity costs $0.15 per kilowatt hour, how much does this cost?

30. DC and AC DC current AC current Direct current
Current or voltage keeps the same direction
AC current
Alternating current
Current or voltage reverses (60 times / sec in US)

31. DC and AC DC current is good for short distances
AC can be converted to lower voltages or DC
AC current can travel over large distances (from power plant)
Transformers convert high voltage to lower voltage

32. Capacitors
Capacitors: devices that store electrical energy by separating charges
Can supply power for a short amount of time
Measured in farads (F)
1 F = 1 coulomb of charge stored using 1 V

33. Capacitors Capacitance depends on 3 things
Surface area of plates
Type of insulator
Distance between the plates
Smaller distance = greater capacitance
Capacitors discharge over time

34. Capacitors
Defibrillators
Subwoofers
Crosswalk lights