Points: ___ /10
Names__________________
Resistance and Ohms Law Investigation
Materials: Computer, Drinking Straw
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.
Procedure Part I Wire Resistance:
1. Blow through the drinking straw.
2. Cut the drinking straw in half and blow through a half-straw.
3. Describe the effect of length on ease to blow air through the straw.
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4. Cut the halves again in half.
5. With the four pieces, blow through one, then blow through all four made into a larger, square-shaped
straw.
6. Describe the effect of straw size (diameter) on ease to blow air through the straw.
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II. Ohms Law Sim
1. Open the Ohm’s Law Sim: http://phet.colorado.edu/sims/ohms-law/ohms-law_en.html
a. Or google: “ohm’s law simulation university of Colorado”
2. Also refer to Battery-Resistor Circuit: http://phet.colorado.edu/en/simulation/circuit-construction-kit-dc
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?
Questions:
1. If the voltage doubles, what happens to the current?
a. What type of relationship do you believe exists between voltage and current?
2. With the Voltage slider set at 4.5 V, move the resistance slider, observing what happens to the current.
a. If the resistance doubles, what happens to the current?
b. What type of relationship do you believe exists between current and resistance?
3. Predict what will happen to the current in a circuit if the voltage is kept constant but the wire diameter is
increased.
4. Predict what will happen to the current in a circuit if the voltage is kept constant but the wire length is
increased.
5. Predict what will happen to the current if the resistance is unchanged but
a. the voltage is increased?
b. the voltage is decreased?
6. 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.
7. Set the Resistance slider to 300 ohms, Use the Voltage slider to adjust the Potential to the values in data
table 1, also recording the resulting electric currents.
Current (mA)
Potential
1.5
3.0
4.5
Current (mA)
Potential
6.0
7.5
9.0
8. Fill in the missing parts of the following table:
Electrical Quantity
Voltage or Potential
Difference
Current
Resistance
Description
Unit
Water Analogy
Volt (V)
Amount of water flowing