Download Resistance and Ohms Law Investigation Period/Names

Resistance and Ohms Law Investigation
Period/Names__________________
______________________________
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Objectives:
1. Discover what parameters affects the resistance, R, in a circuit
2. Investigate Ohm’s Law and discover what conditions maximize current flow.
I. Resistance Sim
1. Goto http://phet-web.colorado.edu
2. Click HTML 5 Simulations at the top
3. Select Resistance in a Wire
A. Manipulate each button separately and in your own words what does each variable represent(look at what
changes)
1. P(Greek letter rho)
2.
L
3.
A
B. Discuss these variables with another Group. Do you agree with what each represents? Make any
corrections if needed.
C. In this simulation what factor(s) increase resistance?
D. What other factor(s) not shown in this simulation might also increase resistance? (Think about reading and
class discussion).

Imagine blowing through a drinking straw. You cut the drinking straw in half and blow through a halfstraw. Describe the effect of length on ease to blow air through the straw.

Imagine cutting the halves again in half. With the four pieces, imagine blowing through one, then blow
through all four made into a larger, square-shaped straw. Describe the effect of straw size (diameter) on
ease to blow air through the straw.
Now, open the PhET Simulation Resistance in a Wire
As wire length (cm) increases, the resistance (Ω) _________________
As wire area (cm2) increases, the resistance (Ω) __________________
As wire density (Ωcm) increases, the resistance (Ω) _______________
II. Ohms Law Sim
1. Close the Resistance in a Wire Sim
2. Open the Ohm’s Law Sim
A. From this Sim explain what each variable represents and give its units
1. V
2.
I
3.
R
B. Manipulate the buttons. What conditions maximize current?
C. What conditions minimize current?
D. Close the program and log out.
Questions:
1. Predict what will happen to the current in a circuit if the voltage is kept constant but the wire diameter is
increased.
2. Predict what will happen to the current in a circuit if the voltage is kept constant but the wire length is
increased.
3. Predict what will happen to the current if the resistance is unchanged but
a. the voltage is increased?
b. the voltage is decreased?
4.
Predict what will happen to the resistance if you change from a copper wire, which is a good
conductor, to an iron wire, which does not conduct as well.
Procedure Part II: Ohm’s Law: Electricity, Magnets, and Circuits  Ohm’s Law
mA is milliamps, and _________ milliamps equals one Ampere.

Move the potential (volts) and resistance (ohms) sliders and observe the current (amps)
As voltage increases, current __________________.
As resistance increases, current ________________.
Fill out the tables below and check your work in the simulation. ( ½ pt each )
 Remember, the simulation shows milliamps.
 You should show Amperes
V
8.0 V
=
I
*
A
2.0 V
R
800 Ω
Ω
.044 A
V
.0058 A
430 Ω
V
.069 A
100 Ω
6.4 V
A
300 Ω
Conclusion Questions: ( ½ pt each)
1.
Incandescent light bulbs have a very thin filament that glows when hot. Thin filaments have very high /
low resistance.
2.
The 12V battery in your car operates a 25 amp car stereo. What is the resistance of this stereo system?
___________
3.
A “2D” Maglite flashlight runs on 3.0V. What is the current through the bulb if resistance is 15 Ω ?
____________
4.
How many volts must an iPod charger provide to charge an iPOD using .85 Amps at 35 Ω?
_____________
5.
You need to buy a long extension cord to power a stereo at your spring break BBQ. You need 200feet.
You have a 50 ft cord that will work. You rationalize that four such 50 ft cords will do the job. Is this a
good idea? Why or Why not?
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