Download Circuit Building Lab

Name ___________________________________
Date ____________
Lab Partners __________________________ ______________________________________
Circuit Building Lab
Purpose:
Up until this point in our electricity unit we have learned both how to calculate the
different values that correspond to circuits, and how to build various series and parallel
circuits. Our next step, and the purpose of this lab will be to join these two skills together.
We will build circuits and using our knowledge of Ohm’s Law and the different circuit
rules, will also find the resistance of various resistors and test our rules. Also, we will
learn to use voltmeters and ammeters.
Materials:
CPO Circuit kit
Voltmeter w/ Wires
DC power supply
Ammeter W/ Wires
Procedure Part 1- Simple Circuit:
1. With your powers supply OFF, turn both voltage knobs all the way down, and turn the
current knob all the way up.
2. Plug in the power supply and turn it on. Adjust the voltage so that it reads 3.0 volts.
Do not touch this setting or the current setting again unless you are told to do so.
3. To refresh your memory of using these circuits and to practice with the power supply, construct a simple
circuit containing a 3-volt power source, a switch, and a light bulb.
4. Draw a circuit diagram of the circuit you have constructed in the space provided below: (Neatness Counts!!)
The first thing that you need to learn how to use is the ammeter. Ammeters, just like wires, have extremely small
resistances. In other words, they allow current to flow through them very easily. For that reason, an ammeter is
connected “in series” with the component of the circuit that you are trying to measure. If instead, you connect an
ammeter in its own path, the circuit will not work. This is called a “short” in the system.
To visualize this, below are some examples of ammeters connected correctly and some that are connected
incorrectly. Notice that the ones that are connected correctly are connected “in series” with the rest of the circuit:
For this circuit:
Correct:
Incorrect:
Procedure Part 2- Ammeter:
1. Construct the same circuit that you built earlier (power source, bulb 1, and switch) but also connect the
ammeter into the circuit.
2. Record the reading from the ammeter on the line: Current through Bulb 1 bulb: _____________
3. Draw a circuit diagram of the circuit you just built (with the ammeter) in the space provided:
Page 1 of 8
Name ___________________________________
Date ____________
Lab Partners __________________________ ______________________________________
4. Replace the bulb 1 bulb in your circuit with the different bulb and record your new current on the line
provided: Current through the second bulb: ___________
Describe the physical differences in the bulbs (they will be referred to as bulb one and bulb 2 for the rest of the
lab.)
Next you need to learn how to use the voltmeter. Voltmeters have almost 100% resistance. In other words they
don’t allow current to flow through them. For that reason, a voltmeter is connected “in parallel” with the
component of the circuit that we are trying to measure. It needs to have its own individual path otherwise it will
block electricity from flowing.
Not only that, but a voltmeter needs to be connected across a “difference of potentials.” To visualize
this, below are some examples of voltmeters connected correctly and some that are connected incorrectly. Notice
that the ones that are connected correctly are connected “in parallel” and “across” components.
For this circuit:
Correct
Incorrect
Procedure Part 3- Voltmeter:
1. Construct the same circuit that you built earlier (power source, bulb 1 bulb, and switch) but also connect the
voltmeter across the bulb.
2. Record the reading from the voltmeter on the line: ________________
3. Draw a circuit diagram of the circuit you just built (with the voltmeter) in the space provided:
4. Now move the voltmeter so it is connected across the power source.
5. Record the reading from the voltmeter on the line: ________________
6. Draw a circuit diagram of the circuit you just built (with the voltmeter) in the space provided:
7. Compare the two voltage readings you just made. Are they basically the same? _______________
8. If the voltage measured across the power source is the total voltage, what does this mean about the voltage
used by the bulb in this circuit?
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Name ___________________________________
Date ____________
Lab Partners __________________________ ______________________________________
Now you have measured the current through each bulb and the voltage in the circuit.
Using the currents, the voltage you measured, and ohm’s law, calculate the resistance of each bulb (show all your
work):
Resistance of bulb 1: _______
Resistance of bulb 2: _______
Procedure Part 4- Series Circuit:
1. Deconstruct any circuit you still have built.
2. Draw a circuit diagram of a 3 volt power supply, a switch, bulb 1, and bulb 2 all IN SERIES. Be sure to
label all the values on the diagram (remember that you found he different resistances earlier in the lab):
3. Complete a VIRP chart for all of the values for this series circuit:
Element
Voltage (V)
Current (A)
Resistance (Ohms)
Power (Watts)
Bulb 1
Bulb 2
Total
4. Redraw the circuit diagram of the series circuit but with the ammeter in the circuit:
5.
6.
7.
8.
Build this circuit.
What was the reading on the ammeter? _____________
Does this match the currents that you calculated in your VIRP chart? ________
If you move the ammeter to different parts of the circuit, what do you think will happen to the reading on
the ammeter?
Page 3 of 8
Name ___________________________________
Date ____________
Lab Partners __________________________ ______________________________________
9. Try reconstructing this circuit with the ammeter at different parts of the circuit. Explain why you were
correct or incorrect in the question before this:
10. Deconstruct the circuit.
11. Redraw the series circuit diagram but with the voltmeter across bulb 1:
12.
13.
14.
15.
Build this circuit.
What does the reading on the voltmeter say the voltage drop in the bulb 1 bulb is? __________
Does this match the voltage drop you calculated for bulb 1 in your VIRP chart? _____
Redraw the series circuit diagram but with the voltmeter across bulb 2:
16. Build this circuit.
17. What does the reading on the voltmeter say the voltage drop in bulb 2 is? __________
18. Does this match the voltage drop you calculated for bulb 2 in your VIRP chart? _____
19. Redraw the series circuit diagram but with the voltmeter across both bulbs:
20. What does the reading on the voltmeter say the voltage drop across both bulbs is? _________
21. Which voltage in your VIRP chart does this reading match up with?
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Name ___________________________________
Date ____________
Lab Partners __________________________ ______________________________________
22. In a series circuit, the sum of the voltage drops across each bulb is equal to the total voltage in the circuit.
Using the data you measured with the voltmeter and the values you calculated in your VIRP chart, verify
this law:
Procedure Part 5- Parallel Circuit:
1. Deconstruct any circuit you still have built.
2. Draw a circuit diagram of your 3 volt power supply, a switch, one bulb 1 bulb, and bulb 2 all IN
PARALLEL. Be sure to label all the values on the diagram (remember that you found he different
resistances earlier in the lab):
3. Construct and complete a VIRP chart for all of the values for this parallel circuit:
4. Redraw the circuit diagram of the parallel circuit but with the ammeter in the circuit BEFORE THE
WIRE SPLITS INTO THE TWO BRANCHES:
5. Build this circuit.
6. What is the reading on the ammeter? ________
7. Which current from your VIRP chart does this reading match?
8. Redraw the parallel circuit diagram but with the ammeter in the branch with BULB 1:
9. Build this circuit.
10. What is the reading on the ammeter? __________
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Name ___________________________________
Date ____________
Lab Partners __________________________ ______________________________________
11. Which current from your VIRP chart does this reading match?
12. Redraw the parallel circuit diagram but with the ammeter in the branch with BULB 2:
13. Build this circuit.
14. What is the reading on the ammeter? __________
15. Which current from your VIRP chart does this reading match?
16. In a parallel circuit, the sum of the currents through each bulb branch is equal to the total current in the
circuit. Using the data you measured with the ammeter and the values you calculated in your VIRP chart,
verify this law:
17. Deconstruct the circuit.
18. Redraw the parallel circuit diagram but with the voltmeter across bulb 1:
19. Build this circuit.
20. What does the reading on the voltmeter say the voltage drop in bulb 1 is? __________
21. Does this match the voltage drop you calculated for bulb 1 in your VIRP chart? _____
22. Redraw the parallel circuit diagram but with the voltmeter across bulb 2:
23.
24.
25.
26.
Build this circuit.
What does the reading on the voltmeter say the voltage drop in bulb 2 is? __________
Does this match the voltage drop you calculated for bulb 2 in your VIRP chart? _____
In a parallel circuit, the voltage drop across each bulb is equal to the total voltage in the circuit. Using the
data you measured with the voltmeter and the values you calculated in your VIRP chart, verify this law:
Page 6 of 8
Name ___________________________________
Date ____________
Lab Partners __________________________ ______________________________________
Extra Stuff:
1. Build a series circuit with two identical bulbs and have your voltage source set at 3 volts.
2. If you add another bulb into this circuit, what do you think will happen to the brightness of the bulbs?
3. Add a third bulb in series into this circuit. What happened to the brightness of the bulbs?
4. Why do you think this happened?
5. Using the resistance of bulb 1 that you found earlier in the lab, and your 3 volt total resistance, complete a
VIRP chart for each of the 2 bulb circuit and the 3 bulb circuits. (2 VIRP Charts)
6. Explain what happened to the bulbs in terms of the current and resistances you just calculated:
7. Deconstruct the circuit.
8. Build a parallel circuit with two bulbs and have your voltage source set at 3 volts.
9. If you add another bulb to this circuit in parallel, what do you think will happen to the brightness of the bulbs?
10. Why do you think this happened? Explain what you think is happening to the current and resistance
throughout the circuit:
Challenge: Determine the resistance of the three resistors.
Red - _____________
Green - ______________________
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Blue - _____________________
Name ___________________________________
Date ____________
Lab Partners __________________________ ______________________________________
Questions:
Remember our new equation for power: P  IV
1. Draw a series circuit with one bulb 1, one bulb 2 and a 3 volt battery (use the resistances from your
observations).
2. Complete a VIRP chart for this circuit but now also calculate the power of each light bulb and the total
power of the circuit.
3. How does the power (wattage) of bulb 1 and bulb 2 compare to bulbs you might use in your house?
4. Draw a parallel circuit with one bulb 1, one bulb 2 and a 3 volt battery (use the resistances from above).
5. Complete a VIRP chart for this circuit and calculate the power of each light bulb and the total power of
the circuit.
6. Do the powers of each individual bulb change?
7. Does the total power of the circuit change?
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