1. April 11, 2008 Get out last night’s homework.
REVIEW
April 11, 2008
Get out last night’s homework.
Find a reliable partner and go over your work together.

2. No Units = Incorrect Answer
REVIEW
1. How much current is there in a 50-ohm lamp bulb connected to a 120-volt wall outlet? Sketch a schematic.
List given information
R = 50 ohms
V = 120 volts
I = ?
Sketch schematic
Write formula and solve
V = I x R
I = V / R
I = 120 / 50
I = 2.4 amps
No Units = Incorrect Answer
R = 50 ohms
120V
I = ?

3. List given information
REVIEW
2. A spot welder produces 150 amperes through a resistance of 0.01 ohms. Sketch a schematic and find the voltage.
List given information
I = 150 amps
R = 0.01 ohms
V = ?
Sketch schematic
Write formula and solve
V = I x R
V = 150 x 0.01
V = 1.5 volts +
R = 0.01 ohms
V = ? -
I = 150 A

4. List given information
REVIEW
3. What is the power available in a house circuit if a 120-volt circuit allows a maximum of 20 amperes?
List given information
V = 120 volts
I = 20 amps
P = ?
Write formula and solve
P = V x I
P = 120 x 20
P = 2400 W
How many kilowatts is this?
2400 / 1000 = 2.4 kW

5. REVIEW
4. Using Ohm’s Law and Joule’s Law, write an equation for power that does not include voltage.

6. Solve either Joule’s or Ohm’s Law for I
REVIEW
5. Using Ohm’s Law and Joule’s Law, write an equation for power that does not include current.
Joule’s Law
P = V x I
Ohm’s Law
V = I x R
Solve either Joule’s or Ohm’s Law for I
V = I x R Ohm’s Law
I = V / R Solve for I
Substitute into other formula:
P = V x I Joule’s Law
P = V x (V / R)
P = V2 x R

7. List given information
REVIEW
6. 3 resistors are in series: 20 ohms, 30 ohms, 40 ohms. What is the total resistance? Sketch a schematic.
List given information
R1 = 20 ohms
R2 = 30 ohms
R3 = 40 ohms
Sketch schematic
Write formula and solve R1 R2 R3
R = R1 + R2 + R3 T
R = T
R = 90 ohms T

8. List given information
REVIEW
7. 4 resistors are in parallel: 20 ohms, 30 ohms, 40 ohms. What is the total resistance? Sketch a schematic.
List given information
R1 = 20 ohms
R2 = 30 ohms
R3 = 40 ohms
Sketch schematic
Write formula and solve R1 R2 R3

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13. Study for Monday’s Test!
REVIEW
CLASSWORK/HOMEWORK
Study for Monday’s Test!