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. 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

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

4. 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

5. 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 = ?

6. 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

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

8. 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

9. 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

10. 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

11. 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

12. 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)

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

14. 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)

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

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

17. 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

18. 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

19. 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

20. 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.