# Phet batteries, resistance, current | Physics homework help

NSET 111

Batteries, Resistance and Current

Name: ____________________________________

The fundamental relationship among the three important electrical quantities current, voltage, and resistance was discovered by Georg Simon Ohm. The relationship and the unit of electrical resistance were both named for him to commemorate this contribution to physics. One statement of Ohm’s law is that the current through a resistor is proportional to the voltage across the resistor and inversely proportional to the resistance.

Current and voltage can be difficult to understand, because they cannot be observed directly. To clarify these terms, some people make the comparison between electrical circuits and water flowing in pipes. Here is a chart of the three electrical units we will study in this experiment.

 Electrical Quantity Description Unit Water Analogy Voltage or Potential Difference A measure of the Energy difference per unit charge between two points in a circuit. Volt (V) Water Pressure Current A measure of the flow of charge in a circuit. Ampere (A) Amount of water flowing Resistance A measure of how difficult it is for current to flow in a circuit. Ohm (W) A measure of how difficult it is for water to flow through a pipe.

Batteries are made by the difference in the electronegativity of different metals.  Electrons can flow spontaneously between metals that give off electrons easier to metals that are less likely to give off electrons.  There is a substance between these metals that allow charge to flow (salt bridge) so net charge doesn’t build up and “turn off” the battery.

PRELIMINARY SEtup and QUESTIONS

1. Start up the PhET Simulation at http://phet.colorado.edu/en/simulation/ohms-law. Click on the “Run Now” button. The screen shown in Figure 1 should appear.

2. With the Resistance slider set at its default value, move the potential slider, observing what happens to the current.

If the voltage doubles, what happens to the current?

3. With the Voltage slider set at 4.5 V, move the resistance slider, observing what happens to the current.

“Ohm’s Law”:

In this sim, vary the values of Resistance (R), Current (I) and Voltage (V).

1.  What are three different combinations of I and R which get a voltage of 6.0 Volts?

2.  Describe the relationship between I and R.  Why is this?

3.  What would happen if you could decrease the resistance to 0?  Explain.

PROCEDURE

1. 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.

Data Table 1:

 Current (mA) Potential Current (mA) Potential 5 20 10 25 15 30

Record the slope of the graph below data table 1.  Calculate the resistance value by taking the slope of the graph times 1000.

2. Switch back to the PhET Simulation. Set the Resistance slider to 600 ohms, Use the Voltage slider to adjust the Potential to the values in data table 2, also recording the resulting electric currents.

Data Table 2:

 Current (mA) Potential Current (mA) Potential 2.5 10 5 12.5 7.5 15

Record the slope of the graph below data table 2.  Calculate the resistance value by taking the slope of the graph times 1000.

3. Switch back to the PhET simulation. Return the Voltage Slider to 4.5 V.  Now we will use the Resistance slider to set the Resistor to the values in the table.  Fill in table 3 with your data:

Record the slope of the graph below data table 3.  Calculate the resistance value by taking the slope of the graph times 1000.

ANALYSIS

Do the experimental data confirm that the Electric Current in a resistor is directly proportional to the electric potential provided by the batteries?

Do the experimental data confirm that the electric current is inversely proportional to the Resistance for a fixed electric potential?

CONCLUSION

Write a conclusion that summarizes the results of this experiment.

1.  What are three different combinations of I and R which get a voltage of 6.0 Volts?

2.  Describe the relationship between I and R.  Why is this?

3.  What would happen if you could decrease the resistance to 0?  Explain.

PROCEDURE

1. 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.