Learning Goals: Students will be able to

• Discuss basic electricity relationships

• Build circuits from schematic drawings

• Use an ammeter and voltmeter to take readings in circuits.

• Provide reasoning to explain the measurements and relationships in circuits.

Before this activity: New terminology

1.  Voltage - the electric potential energy per unit charge.  You can think of voltage as an "electric pressure".  A difference in voltage is needed for charge to move.  Batteries are a source of voltage that makes charges move.

2.  Voltmeter - device to measure voltage.  Touch the two leads to the points that you want to measure the voltage between.

3.  Current - the rate of flow of charge.

4.  Ampere - the unit of electric current. 1 Ampere = 1 Coulomb per second

5.  Ammeter - device to measure electric current.  An ammeter must be inserted into the circuit so that the charges pass through it to measure current.

6.  Resistance - a measure of the resistance to charge flow.

7.  Ohm - the unit of resistance, equal to 1 volt per ampere.

I. Observing voltage relationships

Go to the PHeT web site and use the Circuit Construction Kit simulation (CCK). Drag out three batteries. Measure the voltage of each using the voltmeter and record the voltage in a table like the one shown. Then move the batteries end to end as below to measure combined voltage.

Battery Voltage (V) 1 9  2 9  3 9  1+2 18  1+2+3 27

1. Describe the relationship between the number of batteries and the voltage and explain what you think might be happening.  The Voltage of the entire system is equal to the sum of the voltages of each battery.

2. What could you vary to test your description about the relationship? (Right click on the batteries to change characteristics ) Run several tests recording your data in an organized table. We changed the voltage of the idividual batterys.

   Battery	Voltage (V)
   1	9
   2	15
   3	20
   1+2	24
   1+2+3	44

3. Talk to another group about their description, tests and results. Rewrite your description to include the more broad tests.  The other group did the same tests as us, but with different numbers. They reached the same conclusion.

II. Using voltage

Use the Circuit Construction Kit simulation to build a circuit with a battery and a light bulb in the Lifelike visual mode.

1. Draw what your circuit looks like or upload an .jpg image.          

2. How does the voltage of the battery compare to the light bulb voltage? Explain what you think is happening.          The voltage of the battery is 9, but eh lightbulb has no voltage of it's own.  When the voltage is transferred to the light bulb, the charges make it light up.

3. Vary the voltage of the battery and write observations about how the brightness is affected by voltage.          When the voltage increases, the brightness increases and the charges move more quickly through the circut.  The light also reaches farther.

4. Think about a real light bulb and battery; explain what you think is happening that causes the changes in brightness.          More electrical currents are running through the lightbulb in the same amount of time, which creates more energy to be transferred into light energy.

III. Using voltage in series circuits

Use CCK to build the circuits below with a battery at about 12 volts and light bulbs. Turn on the voltmeter and ammeter to measure voltage of the battery and current into it. Record bulb brightness with descriptive language.

# of bulbs Battery voltage (v) Current into battery (A) Brightness of bulbs 1 12  1.2  burns with a soft, warm glow  2 12  .6  a dying candle  3 12  .4  like the last rays of sunlight through a dusty window

1. Summarize the relationships you observed and explain what you think is happening.          The current emitted from the battery is being divided between the different lightbulb, causing the brightness of the bulbs to fall with each addition.

2. Test to see if changing the battery voltage causes you to modify any of your conclusions. Explain what you measured and any conclusions you draw from your tests.          We measured the current on the same systems with a battery of 50 V and came to the same conclusions.

3. What happens when you take a wire out of a circuit? Explain what you think is happening          Nothing changes, because the wire doesn't have its own voltage and merely serves as transportation for a charge.

4. Test using the voltmeter or ammeter in different ways. For example: Does it matter if you take the reading on the left or right of the battery? Switch the meter ends? Describe your tests and results.          The voltage and the current are consistent through out the system, no matter where we test it.  All of our tests were consistent.

IV. Using voltage in parallel circuits

# of bulbs Battery voltage (v) Current into battery (A) Brightness of bulbs 1 15  1.5  Like a flashlight with new batteries  2 15  1.5  With the same intensity as its predecessor   3 15  4.5 Still with the same intesity

1. Summarize the relationships you observed and explain what you think is happening. The lightbulb brightness was not affected by the number of bulbs attached to the system.

2. Test to see if changing the battery voltage causes you to modify any of your conclusions. Explain what you measured and any conclusions you draw from your tests.  It does not change our conclusion, it only bolsters it because all of the lightbulbs make the same adjustments.

3. What happens when you take a wire out of a circuit? Explain what you think is happening Part of the circut breaks and the lightbulb conected to the break shuts off. The others continue shining.

4. Test using the voltmeter or ammeter in different ways. For example: Does it matter if you take the reading on the left or right of the battery? Switch the meter ends? Describe your tests and results.           It changes throuhg the circut because some of the energy from the battery is given to each light bulb.  However, since each bulb is given the same amount, they glow in unison. 

V. Observing voltage and current relationships with resistors

Use CCK to build the circuit below. Vary the voltage of the battery (use five different values). Record the battery voltage and the current in the circuit in a table.

Battery Voltage Circuit Current 10  1  20  2  30  3  40  4  100  10

1. Explain what might be happening to cause the change in current.          The increase in the voltage of the battery, releasing more charges.

2. Create a graph to determine the relationship between current and voltage.  Upload an image of  your graph (use Google Spreadsheets or Excel).  How are current and battery voltage related? What is the shape of the graph? 

    The current and the voltage have a direct relationship.

3. Describe how you could use the simulation to verify the relationship. Test your ideas and make modifications to your original answers if necessary. Be sure to explain your reasoning. We could change the voltage and measure te change.

VI. Observing voltage and current relationships for variable resistors.

Build the circuit below. Vary the value of resistor at least ten times. Record in a data table: resistance, current and voltage for each trial.

Resistance(Ohm) Current(a) Voltage(V) 1 9  9 2 4.5 9 3  3 9 4 2.25 9 5 1.8 9 6 1.5 9 7  1.29 9 8 1.12  9 9 1 9 10 .9 9

1. Graph current vs resistance and determine the algebraic relationship for resistance and current.  Upload an image of the graph you created (use Google Spreadsheets or Excel) with a best-fit line or curve.  Record the equation of the best-fit line or curve.  

2. Graph voltage vs. resistance and determine the algebraic relationship for resistance and voltage.  Upload an image of the graph you created (use Google Spreadsheets or Excel) with a best-fit line or curve.  Record the equation of the best-fit line or curve.

3. Explain the relationships in terms what you think is happening in the circuit. Include how this experiment is like the one where you added light bulbs. The current matches the the voltage. Just like in the other experiments.