Download Wire Resistance and Ohm`s Law

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Wire Resistance and Ohm’s Law PhET Lab
Introduction: When an electrical potential exists in a circuit, a current may flow. Current is the flow of electrons in a circuit.
Resistance in the circuit slows the flow of the electrons, reducing the current in the circuit. We will use the mathematical form of
Ohm’s Law frequently when we investigate electric current and circuits later in this unit.
You will need to get online and go to tinyurl.com/marentette-wiki (the wiki website for the class). From there go to Honors
Physics and click on the link for today.
Procedure Part I:
1. mA is milliamps, and _________ milliamps equals one Ampere.
2.
Move the potential (volts) and resistance (ohms) sliders and observe the current (amps)
As voltage increases, current __________________.
As resistance increases, current ________________.
3.
Fill out the tables below and check your work in the simulation.
a. Remember, the simulation shows milliamps.
b. You should show Amperes
V
=
I
*
R
1/R
8.0 V
800 Ω
A
2.0 V
Ω
.044 A
V
.0058 A
430 Ω
V
.069 A
100 Ω
4. Compute the 1/ R value and enter it into the last column.
5. Construct a graph of Current (y-axis) versus 1/Resistance (x-axis). Include a title for the graph,
properly label both the X and Y axis, find the slope of a best fit linear line. (5pts)
6.
What Physics quantity (physics word we studied) is the slope of the graph?
Voltage/Resistance/Current
7. Now go to the ‘Resistance in a Wire’ simulation and answer the following questions.
8. Increase the resistivity to .75Ω.
a. What happens to the resistance? Increases/decreases/doesn’t change
9. Return the resistivity to .5Ω cm and increase length to 12cm.
a. What happens to resistance and the wire? Increase/decrease/doesn’t change
10. Return the length to 10cm and increase area to 6.98cm². What happens to resistance?
Increase/decrease/doesn’t change
11. What is the relationship between
a. A and R? direct/inverse/none
b. ρ and R? direct/inverse/none
c. L and R? direct/inverse/none
12. Incandescent light bulbs have a very thin filament that glows when hot. Thin filaments have very high /
low resistance.
Scroll down to the next simulation. This one you click on the picture to run it. Wouldn’t it be great to see inside wires and electrical
devices, to actually watch the electrons flow? This simulation allows us to do this. In this simulation, you will build simple and
compound circuits and measure their potential (voltage), current, and resistance.
Procedure:

Click on Schematic Visual

To add elements to your circuits, simply drag an item into the work area.




To remove an item or change it, right-click the item you wish to change.
To uncouple two circuit elements, right click on the circular junction and choose “split junction.”
To measure voltage and current, click on the boxes to the right.
Remember, voltage is read in parallel (outside of the circuit), while current is
read in series (in the circuit)
Part I: DC Circuits in Series

Build a simple circuit made of one battery and one light in a single loop.
1.
Use a voltmeter to find the voltage across the light.
Light: ________________ Volts
2.
Use an ammeter to find the current through the lightbulb
Light: ________________ Amps
3.
Use Ohm’s Law V  IR to find the resistance of the light
4.
Set both of the voltmeter’s probes on the same side of a light. What is the voltage? _____ Why? ________________
5.
Reverse the battery (right click on it and choose reverse). What happens to the flow of electrons?
Light: ________________ Ohms
______________________________________________
6.
Build a circuit with a battery and three lights in series.
What are the voltages across each item in the circuit? (.5 pts each)
Light 1: ________________ Volts
Light 2: ________________ Volts
Light 3: ________________ Volts
Battery: ________________ Volts
.
7.
What is the current in each part of the circuit? (.5 pts each)
Between Battery and Light 1: _____________ Amps
Use Ohm’s Law to find the resistance of the lights
Between Lights 1-2: __________________ Amps
Light 1: ________________ Ohms
Between Lights 2-3: __________________ Amps
Light 2: ________________ Ohms
Light 3: ________________ Ohms
8.
Are all the lights the same brightness? _______
9.
Add additional batteries in series with the first battery. (making sure you connect the positive of one battery to the negative
of the next battery).
What happens to the brightness? _________________the voltages? _________________the currents? _________________
10. Add a resistor to your series circuit.
What effect did the resistor have on the lights in the circuit? _________________________________________________
11. Create a wire path in your circuit that bypasses all the lights. This is a short circuit.
What happens to the battery in short circuit? _________________________ The lights? ___________________________
What happens to electrons that are not slowed by the resistance of lights? ________________________________________
Part II: DC Circuits in Parallel
12. Build a circuit with a battery and three lights in parallel with the
battery
What are the voltages across each item in the circuit? (.5 pts each)
Light 1: ________________ Volts
Light 2: ________________ Volts
Light 3: ________________ Volts
Battery: ________________ Volts
What is the current in each part of the circuit?
Light 1’s path: __________________ Amps
Use Ohm’s Law to find the resistance of the lights
Light 2’s path: __________________ Amps
Light 1: ________________ Ohms
Light 3’s path: __________________ Amps
Light 2: ________________ Ohms
Battery: ________________________Amps
Light 3: ________________ Ohms
13. Add additional batteries in series with the first battery.
What happens to the brightness? _________________the voltages? _________________the currents? _________________
14. Add a resistor to one path in your parallel circuit.
What effect did the resistor have on the light in its path? _____________________________________________________
What effect did the resistor have on the lights in the other two paths? ___________________________________________
Part III: Compound Circuits
15. Build the circuit illustrated below. Use two batteries in series.
A
B
C
Which light is the brightest? _______________ (.5 pts each)
What is the voltage across?
What is the current through?
What is the resistance of?
Light A: ______________ Volts
Light A: _____________ Amps
Light A_____________ Ohms
Light B: ______________ Volts
Light B: _____________ Amps
Light B_____________ Ohms
Light C: ______________ Volts
Light C: _____________ Amps
Light C_____________ Ohms
Battery: ______________ Volts
Battery: _____________ Amps
Battery_____________ Ohms
Conclusion Questions and Calculations:
1.
To assure the same voltage is available to all devices; my house is wired in series / parallel.
2.
My TI calculator uses four 1.5 V AAA batteries. The effectual voltage needed by the calculator must be___________.
3.
A flashlight bulb with a potential difference of 6.0 V across it has a resistance of 8.5 . How much current is in the bulb filament?
______________
For Extra Credit: 1 pt per “ohmisim” for up to 3 pts extra credit. Please do not use ohmisims from class.
Create your own “ohmisim”. Draw a picture and label it.
For example
“Ohm” sweet “ohm”