1. U3e-L3
February 25, 2010
DRILL
Why are the + and – symbols unnecessary when drawing the power source in an electric schematic?
A ______ circuit occurs when the positive terminal is connected directly to the negative terminal by a conductor, with no resistance.
Short
1. The length of the lines tell you which is positive and which is negative

2. What is the difference between an open circuit and a closed circuit?
A closed circuit is one in which the pathway of the electrical current is complete and unbroken.
An open circuit is one in which the pathway of the electrical current is broken. A switch is a device in the circuit in which the circuit can be closed (turned on) or open (turned off).

3. Which of the following is a schematic?
U3e-L3
Electric Schematics
What is a schematic?
Which of the following is a schematic?
A schematic is a diagram that represents the elements of a system without using realistic pictures

4. Circuit Schematics Series connection Parallel connection
Resistors connected in series
Resistors connected in parallel
Series connection
Connected along a single path
Same current
Parallel connection
Split and merge
Same voltage

5. Complete problem #5 on your worksheet
U3e-L3
Problems – Joule’s Law
Complete problem #5 on your worksheet

6. U3e-L3
Problems – Joule’s Law
A Honda Insight (hybrid) has a 144 Volt battery system in its trunk. The electric motor that the batteries power can generate 20,000 Watts of power. Sketch a schematic diagram of this circuit. What is the current traveling through this high voltage circuit?
Write the given information:
V = 144 volts
P = 20,000 watts
I = ?
A schematic is a diagram that represents the elements of a system without using realistic pictures

7. Problem #5 – Joule’s Law Write the given information: V = 144 Volts
U3e-L3
Problem #5 – Joule’s Law
Write the given information:
V = 144 Volts
P = 20,000 Watts I = ?
Sketch a schematic diagram of the circuit:
Start with power source
Add conductors
Add load
Add current +
P = 20,000 W
V = 144V -
I = ?

8. Problem #5 – Joule’s Law Write the given information: V = 144 Volts
U3e-L3
Problem #5 – Joule’s Law
Write the given
information:
V = 144 Volts
P = 20,000 Watts I = ?
Rearrange, Substitute, and Solve
Sketch a schematic diagram of the circuit:
R = ? 5V
.7A
P = V x I
I = 20,000W / 144V
R = A
I = P / V

9. Homework Problems #2 and 3 Review
U3e-L3
Problems – Joule’s Law
Homework Problems #2 and 3 Review

10. Homework Problem #2 Write the given information: V = 9 Volts
U3e-L3
Homework Problem #2
Write the given
information:
V = 9 Volts
I = .02 Amps
R = ?
Rearrange, Substitute, and Solve
Sketch a schematic diagram of the circuit:
R = ? 9V
.02A
V = I x R
R = 9V / .02A
R = 450 W
R = V / I

11. U3e-L3
Homework Problem #3
Write the given
information:
V = 120 Volts
I = 5 Amps
R = ?
Rearrange, Substitute, and Solve
Sketch a schematic diagram of the circuit:
R = ?
120V 5A
V = I x R
R = 120V / 5A
R = 20 W
R = V / I
This is how alternating current (AC) power sources are represented schematically

12. Electric Circuits What is a circuit?
A closed path through which an electric current may flow
Closed loop network of electrical elements
through metal objects, outlet plugs, travel in circles

13. Direct Current The unidirectional flow of electrons.
U3e-L1
Direct Current
The unidirectional flow of electrons.
Direct current is current travelling in 1 direction – from the negative terminal to the positive terminal.
Direct current is used in almost all electronic systems as the power supply.
Batteries are a sign of direct current.
one I

14. Direct Current Measuring the voltage of a direct current power supply:
U3e-L3
Direct Current
Measuring the voltage of a direct current power supply:
The voltage is constant.
1.5 V

15. U3e-L3
Direct Current
If voltage is constantly 1.5 V, what does its graph over time look like?
1.5 V
Voltage (volts)
Time (seconds)

16. U3e-L3
Alternating Current
Electrons flow back and forth through an electric circuit.
Most artifacts you plug in.
R = ?
120V
120 V + -

17. U3e-L3
Alternating Current
If voltage is alternating 120 V to -120 V, what does its graph over time look like?
+/-120 V
Voltage (volts)
Time (seconds)

18. What are batteries?
Batteries are composed of a chemical substance which can generate voltage which can be used in a circuit.
There are two kinds of batteries: dry cell and wet cell batteries. Below is an example of a dry cell.
The zinc container of the dry cell contains a moist chemical paste surrounding a carbon rod suspended in the middle.

19. Wet cell batteries are most commonly associated with automobile batteries.
A wet cell contains two connected plates made of different metals or metal compounds in a conducting solution. Most car batteries have a series of six cells, each containing lead and lead oxide in a sulfuric acid solution.

20. What are electric circuits?
Circuits typically contain a voltage source, a wire conductor, and one or more devices which use the electrical energy.
What is a series circuit?
A series circuit is one which provides a single pathway for the current to flow. If the circuit breaks, all devices using the circuit will fail.

21. Resistance Calculations
U3e-L3
Resistance Calculations
Resistors in series are added: R1 R2 R3
Total Resistance:
R = R1 + R2 + R3 T

22. What is a parallel circuit?
A parallel circuit has multiple pathways for the current to flow. If the circuit is broken the current may pass through other pathways and other devices will continue to work.

23. Resistance Calculations
U3e-L3
Resistance Calculations
Resistors in parallel: add their reciprocals R1 R2 R3
Total Resistance: =
R R1 + R2 + R3 T

24. Resistance Calculations
U3e-L3
Resistance Calculations
Calculate the resistance in the following circuit:
100 W
100 W
100 W
Total Resistance:
R = R1 + R2 + R3 T
R = 100 W W W T
R = 300 W T

25. Resistance Calculations
U3e-L3
Resistance Calculations
Calculate the resistance in the following circuit:
100 W
100 W
100 W
Total Resistance: =
R R1 + R2 + R3 T

26. Resistance Calculations
U3e-L3
Resistance Calculations = = + +
R R1 + R2 + R3 T 1 = R T 1 =
.03
(Multiply both sides by Rt) R T
1 = .03 x Rt
Rt = 33.3 W

27. Solve for V, I, R, and P for each of the six problems.
U3e-L3
CLASSWORK/HOMEWORK
Complete the worksheet on electrical problems using Joule’s and Ohm’s Laws.
Solve for V, I, R, and P for each of the six problems.