Electric Currents and Circuits:
Experiment 1: Measuring Current in a Circuit
Pre Lab: Points to Remember:
1. The number of electrons or the amount of electrical charge that passes through a point in the circuit
every second is called current.
2. Electrical current is measured in units called amperes or amps, for short.
3. An ammeter is an instrument that measures the amount of current flowing at a specific position in a
circuit
4. In order for an ammeter to measure the current flowing in the circuit, it must be connected in such a way
so that all of the current passes through the ammeter. In other words, ammeters must be connected in
series in the circuit. Ammeters pose little or no resistance to the flow of current in the circuit.
Symbols to Know:
Dry Cell -
Switch –
Ammeter -
Resistor -
wire –
Light Bulb -
Voltmeter –
Procedure - Part A
1. Set up the circuit as shown in the diagram on the board with R1 in the circuit and the
ammeter at position A1.
2. Close the switch and record the ammeter reading. Open the switch.
3. Repeat the experiment with the ammeter in position A2. Record the ammeter reading.
4. Repeat the experiment with the ammeter in position A3. Record the ammeter reading.
Procedure - Part B:
1. Replace R1 in the Circuit with R2 and repeat the three recordings with the ammeter in the three different
positions.
Data:
R1 Ammeter Readings
(Part A)
R2 Ammeter Readings
(Part B)
Position A1
__________________
__________________
Position A2
__________________
__________________
Position A3
__________________
__________________
Conclusion Questions:
1. Compare the ammeter readings in Part A. What do you conclude?
2. Does it matter where you place the ammeter in this circuit? Why or why not?
3. Compare the amount of current flowing through R1 with the current flowing through R2.
What do you conclude?
4. Which resistor has more resistance, R1 or R2? Give a reason for your answer.
Experiment 2: Current in Series and Parallel Circuits
Pre-Lab: Points to Remember1.
2.
3.
4.
Circuits that have only one possible pathway for the current to flow are called series circuits.
Circuits that have more than one pathway are called parallel circuits.
In series circuits, all of the current must flow through every component.
In parallel circuits, the current may split into two or more pathways so there are places where different
amounts of current will flow.
Procedure - Part A:
1.
2.
3.
4.
5.
Set up the circuit as shown on the board with R1 and R2 arranged in series.
Close the switch and record the ammeter reading. Open the switch.
Repeat the experiment with the ammeter in position A2. Record the ammeter reading.
Repeat the experiment with the ammeter in position A3. Record the ammeter reading.
Repeat the experiment with the ammeter in position A4. Record the ammeter reading.
Procedure - Part B:
1.
2.
3.
4.
Set up the parallel circuit as shown in the diagram above with R1 and R2 arranged in parallel.
With the ammeter at position A1, close the switch and record the ammeter reading.
With the ammeter at position A2, close the switch and record the ammeter reading.
With the ammeter at position A3, close the switch and record the ammeter reading.
Data:
Ammeter Readings
(Part A)
Ammeter Readings
(Part B)
Position A1
__________________
__________________
Position A2
__________________
__________________
Position A3
__________________
__________________
Position A4
_________________
Conclusion Questions: Part A (resistors in series)
1. Compare the four ammeter readings in Part A. What do you conclude?
2. How does the amount of current flowing through R1 and R2 in series compare with the
amount of current flowing through R1 and R2 separately from Experiment 1?
3. What will happen to the amount of current flowing in a circuit as more resistors are added in
series?
4. What happens to the resistance in the circuit as more resistors are added in series?
Conclusion Questions: Part B (resistors in parallel)
1. Look at your circuit diagram for Part B. Which ammeter position would correctly
measure the total amount of current flowing through the entire circuit?
2. What was the total current flowing through your parallel circuit? (A1)
3. Add your current flows through each separate resistor (A2 + A3).
4. Compare your answers from the previous two questions. What do you conclude?
5. Compare the amount of current flowing through R1 (A2) in this experiment with the amount
of current that flowed through R1 in Experiment 1 (Exp. 1, Part A). What do you conclude?
6. Compare the amount of current flowing through R2 (A3) in this experiment with the amount
of current that flowed through R2 in Experiment 1 (Exp. 1, Part B). What do you conclude?
7. What will happen to the total amount of current flowing in a circuit as more resistors are
added in a parallel arrangement?
8. What will happen to the resistance in a circuit as more resistors are added in parallel?
Experiment 3: Voltage Drops in a Circuit
Pre-Lab: Points to Remember:
1.
2.
3.
4.
5.
Voltage is the difference in the electrical charge or potential between two points.
Voltage provides the force that drives electrons through a circuit.
A voltmeter measures the difference in electrical potential in units called volts.
Voltage is also described as: potential difference and electromotive force.
Voltmeters have high resistance and are always connected in parallel in the circuit. No
current flows through the voltmeter when connected in this arrangement.
Procedure - Part A: Voltage of a Dry Cell:
1. Connect the terminals of a voltmeter to the terminals of dry cell with 2 connecting
wires in the arrangement shown on the board. Record the voltmeter reading in the space
provided on the data table.
Procedure - Part B: Voltage Drops Across Circuit Components
1. Set up the circuit as shown on the board.
2. Connect the negative wire from the voltmeter to point A and the positive one to point B.
Close the switch and record the voltage drop at AB on your data table. Open the switch.
3. Connect the negative voltmeter wire to point D and the positive wire to point C. Close the
switch and record the voltage drop at CD on your data table. Open the switch.
4. Connect the negative voltmeter wire to point F and the positive wire to point E. Close the
switch and record the voltage drop at EF on your data table. Open the switch.
5. Connect the negative voltmeter wire to point A and the positive wire to point F.
Close the switch and record the voltage drop at FA on your data table. Open the switch.
6. Connect the negative voltmeter wire to point C and the positive wire to point B. Close the
switch and record the voltage drop at BC on your data table. Open the switch.
Data: Part A
1. Voltage of Dry Cell: __________
Data: Part B
1. Voltage Drop AB:
__________
4. Voltage Drop FA:
__________
2. Voltage Drop CD:
__________
5. Voltage Drop BC:
__________
3. Voltage Drop EF:
__________
Conclusion Questions:
1. Compare the voltage of the dry cell the total voltage drop through the circuit as measured
at position AB. How does the voltage of the dry cell compare to the total voltage drop in
the circuit?
2. Compare the voltage drop through the entire circuit at AB with the voltage drop through the
resistor at position EF. What device causes most of the voltage drop in this circuit?
3. How can you account for the voltage drops at BC, CD, and FA?
Experiment 4: Voltage Drops in a Series Circuit
Pre-Lab: Points to Remember:
1. The greater the resistance of a component, the greater the voltage drop will be through it.
2. The total voltage drop in a circuit must equal the sum of all of the individual voltage drops
through each component in the circuit.
Procedure - Part A: First Arrangement:
1. Set up the circuit as shown on the board with both resistors (R1 and R2) connected in
series. Note the relative positions of the resistors in the circuit.
2. With your voltmeter, measure the voltage drops between the following points: AB, CD, DE,
and CE.
Procedure - Part B: Second Arrangement:
1. To set up the arrangement shown in the diagram above, merely switch the positions of R1
and R2 relative to each other.
2. With your voltmeter, measure the voltage drops between the following points: AB, CD, DE,
and CE.
Data Table:
Part A
Part B
Voltage Drop at AB
__________
__________
Voltage Drop at CD
__________
__________
Voltage Drop at DE
__________
__________
Voltage Drop at CE
__________
__________
Conclusion Questions: Part A:
1. Compare the voltage drop through both resistors at position CE with the sum of the voltage drops of the
two resistors at positions CD and DE. What do you conclude?
2. Compare the voltage through the entire circuit at AB with the voltage drop through
the two resistors at CE. What causes most of the voltage drop in this circuit?
3. Predict what the voltage drop would be at BC:
Conclusion Questions: Part B:
1. Does the order in which resistors are placed in a series circuit affect the voltage drops at different places
in the circuit? Explain.
Experiment 5: Voltage Drops in a Parallel Circuit
Procedure
1. Set up the circuit as shown on the board with both resistors (R1 and R2) connected in parallel.
Note the relative positions of the resistors in the circuit.
2. With your voltmeter, measure the voltage drops between the following points: AB, CD, EF,
and GH.
Data Table:
Voltage Drop at AB:
__________
Voltage Drop at CD:
__________
Voltage Drop at EF:
__________
Voltage Drop at GH:
__________
Conclusion Questions:
1. What do you conclude about the voltage drops across different resistors in a parallel
circuit?
2. How do you account for the values that you obtained in this experiment?
Experiment 6: The Relationship Between Current Flow and Voltage Drop in a Resistor
Pre-Lab: Points to Remember:
1. In this experiment you will measure the voltage drop and current flow through each of your resistors, R1
and R2 that flows in your circuits using different batteries or dry cells.
3. Notice that the ammeter is not installed in the circuit next to the fixed resistor. Since in this circuit there is
only one path for the current to flow, the ammeter readings will be the same no matter where the ammeter is
positioned.
Procedure: Part A:
1. Arrange the circuit as shown on the board with the voltmeter connected in parallel across the fixed
resistor R1 with the battery voltage set at Setting #1. Close the switch and record the ammeter and
voltmeter readings on your data table.
2. Change the battery voltage to Setting #2. Again, close the switch and record the ammeter and
voltmeter readings on your data table.
3. Follow the above procedure changing the battery to voltage settings #3, #4, and #5.
Data Table: Part A (R1)
Battery Voltage Setting:
Voltage
Current
Voltage/Current
1. (minimum)
_______
_______
_____________
2.
_______
_______
_____________
3.
_______
_______
_____________
4.
_______
_______
_____________
5. (maximum)
_______
_______
_____________
Procedure: Part B:
1. Remove R1 from the circuit and replace it with R2.
2. Repeat steps 1-3 from the procedure for Part A.
Data Table: Part B (R2)
Battery Voltage Setting:
Voltage
Current
Voltage/Current
1. (minimum)
_______
_______
_____________
2.
_______
_______
_____________
3.
_______
_______
_____________
4.
_______
_______
_____________
5. (maximum)
_______
_______
_____________
Graph: Construct a graph of your data plotting voltages on the vertical (y) axis and current readings on the
horizontal (x) axis for each resistor, R1 and R2. Connect the data points of each resistor with a straight
line. (you should have two lines on your graph.)
Voltage Drop (Volts)
Current Flow (Amps)
Conclusion Questions:
1. Why are R1 and R2 called fixed resistors?
2. Using your graph, predict what the voltage drop across R2 would be if the current flow was 0.5 amps.
3. Using your graph, predict how much current would flow through R1 if the voltage drop was 17 volts.
4. Ohm’s Law defines the relationship between voltage drop, current flow, and resistance in a circuit.
a. Write a statement that describes Ohm’s Law:
b. Write a formula to calculate the resistance in a circuit when voltage drop and current flow are
given:
c. Write a formula to calculate the voltage drop in a circuit when the resistance and current flow are
given:
d. Write a formula to calculate the current flowing in a circuit when the voltage drop and resistance
are given:
Problems:
Show your work in 3 steps:
1. A 6.0 volt flashlight bulb draws .05 amps of current. Calculate the resistance of the bulb.
2. A microwave oven operates on a 110 volt system and has 22 ohms of resistance.
Calculate the current that the microwave oven draws:
3. A car radio has 10 ohms of resistance and requires 1.2 amps of current. What voltage is required
to operate the radio?
Experiment 7: The Resistance of Two Resistors in Series and in Parallel
Procedure: Part A
1. Arrange the circuit as shown in the diagram above with your voltmeter connected in parallel
across resistor R1.
2. Close the switch and record the ammeter and voltmeter readings on the data table.
3. Replace resistor R1 with Resistor R2 in the circuit.
4. Close the switch and record the ammeter and voltmeter readings on the data table.
5. Calculate the resistance of R1 and R2 seperately and report your answers on the data table
Procedure: Part B
1. Arrange the circuit as shown in the diagram above with your voltmeter connected in parallel
across both resistors, R1 and R2 arranged in series.
2. Close the switch and record the ammeter and voltmeter readings on your data table.
3. Calculate the resistance of R1 and R2 in series and report your answer on the data table.
Procedure: Part C
1. Arrange the circuit as shown in the diagram above with you voltmeter connected in parallel
across both resistors, R1 and R2 arranged in parallel.
2. Close the switch and record the ammeter and voltmeter readings on you data table.
3. Calculate the resistance of R1 and R2 in parallel and report your answer on the data table
Data Table:
Trial:
Voltage
Current
Resistance
Part A
R1
______
______
________
Part A
R2
______
______
________
Part B
R1 & R2 - Series
______
______
________
Part C
R1 & R2 - Parallel
______
______
________
Conclusion Questions:
1. Write a general equation to show how to calculate the resistance of 2 or more resistors
arranged in series.
2. Compare the resistance of resistors in parallel with that of resistors in series.
3. Explain why the resistance calculated for R1 and R2 in parallel was the lowest of all
of your values.
Critical Thinking and Problem Solving:
Use the diagram below to answer the following questions and solve the problems. Show your work appropriately
and label all measurements. You will need to draw this in below.
Ammeter and Voltmeter Readings:
1.
What type of circuit is shown?
2.
What is the voltage of a dry cell?
3.
How much current would be flowing at point F?
4.
Calculate the resistance of the light bulb:
5.
Calculate the resistance of the rheostat:
6.
Predict the voltage drop across E-F:
7.
Calculate the resistance of the fixed resistor:
8.
What is the total resistance in the circuit?
Ammeter Reading:
Voltage Drop A-B:
Voltage Drop G-H
Voltage Drop I-J:
0.5 amps
6.0 volts
3.5 volts
1.5 volts