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COURSE TITLE : Physical Science
AUTHOR : Kim Febres
TOPIC : Ohm's Law; Introductory Physics standards 5.4, 5.5
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ESSENTIAL QUESTION: How do static charges build up?
CULMINATING TASK: Students will create in writing a piece that describes, discusses, and relates the phenomenon of static electricity in their own home.
PERFORMANCE OBJECTIVES:
The student will be able to:
1. define the appropriate vocabulary regarding ohm's law.
2. calculate current.
3. calculate voltage.
4. calculate resistance.
5. identify the units used to measure the properties of ohm's law.
ACTIVITY # 1:
The complete expression called Ohm's Law identifies the relationship among current, voltage, and resistance. When a wire is connected to the terminals of a source, a complete path called a circuit is formed. Charge can flow through a circuit. A flow of charge is called an electric current. The higher the electric current in a wire, the more electric charges that are passing through. The symbol for current is the letter (I). The unit in which current is measuredis the amphere (A). The amphere, or amp for short, is the amount of charge that flows past a point per second.
The amount of work required to move a charge between two points, or the work per unit charge, is called the electric potential difference between the two points. The unit used to measure electric potential is called the volt or voltage (V).
Ohm's Law states that the current in a wire (I) is equal to the voltage (V) divided by the resistance (R). As an equation Ohm's Law is written like this:
Current = Voltage
I = V
Amperes = Volts
Resistance
R
Ohms
If the resistance in a wire is 75 ohms and the voltage is 12 volts, the current is 12/75 , or 0.16ampere. You can rearrange the equation in order to calculate resistance or voltage. The equations for resistance and voltage are as follows:
Resistance =
Voltage
R = V
ohms = volts
Current
I
amperes
Voltage = Current x Resistance V = I x R volts = amperes x ohms
ACTIVITY # 2
1. What is electric current? _____________________________________________________
2. What is resistance? _________________________________________________________
3. What is voltage? ___________________________________________________________
4. How is electric current related to voltage? _________________________________________
ACTIVITY # 3
Calculate the following problems using the formulas above.
Calculating Current
1. What is the current produced with a 9-volt battery through a resistance of 100 ohms?
2. Find the current when a 12-volt battery is connected through a resistance of 25 ohms.
3. If the potential difference is 120 volts and the resistance is 50 ohms, what is the current?
4. What would be the current in Problem 3 if the potential difference were doubled?
5. What would be the current in Problem 3 if the resistance were doubled?
Calculating Voltage
6. What voltage produces a current of 50 amps with a resistance of 20 ohms?
7. What voltage produces a current of 500 amps with a resistance of 50 ohms?
Calculating Resistance
8. What resistance would produce a current of 200 amperes with a potential difference of 200 volts?
9. A 12-volt battery produces a current of 25 amperes. What is the resistance?
10. A 9-volt battery produces a current of 2.0 amperes. What is the resistance?
11. An overhead wire has a potential difference of 2000 volts. If the current flowing through the wire is one million amperes, what is the resistance of the wire?
12. What is the resistance of a light bulb if a 120-volt potential difference produces a current of 0.8 amperes?
Now read information about static electricity.