Name: _____________________Score________/55pts (1pt per question unless marked otherwise)

Wire Resistance and Ohm’s Law PhET LabIntroduction: 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/R8.0 V A 800 Ω

2.0 V .044 A Ω

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/noneb. ρ and R? direct/inverse/nonec. 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 to find the resistance of the light Light: ________________ Ohms

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?

______________________________________________

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.

Which light is the brightest? _______________ (.5 pts each)

A

CB

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”