Download Data and Observations for Part B: Parallel Circuits

Series and Parallel Circuits Lab (Guided)
PSI Physics: Current and DC Circuits
Name____________________________________
An Experiment to Investigate Series and Parallel Circuits Using Ohm’s Law
Problem: What are the relationships between current, voltage, and resistance in parallel
circuits?
For reference, see: http://njc.tl/182
Theory:
When resistors are connected in series in a circuit, the current must flow through
each resistor. Therefore, the total resistance of a series circuit is the sum of the
resistances of the individual resistors in the circuit.
When resistors are connected in parallel in a circuit, each resistor provides a
different path for the electrons to flow, therefore, reduces the total resistance on the
current. When resistors are added in parallel to the junction points, it adds another path
the current may flow through so there is less total resistance between the junction
points. Each time a resistor is added in parallel with another resistor, the total resistance
decreases. The total resistance can be found mathematically by applying the equation:
1 = 1 + 1 + 1 +
RT R1
R2
R3
etc…
.
During this investigation, you will use two resistors determine how these resistors
combine when they are connected in series and a parallel. You will move the ammeter
and voltmeter in each trial on each circuit to determine current and voltage at different
points on the circuit.
Materials:
Battery
Ammeter
Part A: Series Circuit
Procedure:
Connecting wires
Voltmeter
Two resistors
Knife switch
1. Arrange two resistors in series with each other with the ammeter in series before
the resistors and the voltmeter across the two resistors as seen in figure 1.
Record the Current as It and the Voltage as Vt on the data table. This is the
current leaving the battery and the voltage across the resistors.
2. Repeat for the setup in figure 2 and record the Current as I1 and the Voltage as
V1 on the data table. This is the current left after the first resistor (R1) and the
voltage across R1.
3. Repeat the setup in figure 3 and record the Current as I2 and the Voltage as V2
on the data table. This is the current left after the second resistor (R2) and the
voltage across R2.
Series Circuits Data Table
Trial 1
It
Vt
Trial 2
I1
Trial 3
V1
I2
V2
Part B: Parallel Circuits
Procedure:
1. Arrange two resistors in parallel with each other with the ammeter in series
before the junction point a and the voltmeter across the two junction points as
seen in figure 1. Record the Current as It and the Voltage as Vt on the data
table. This is the current leaving the battery and the voltage across the resistors.
2. Repeat for the setup in figure 2 and record the Current as I1 and the Voltage as
V1 on the data table. This is the current flowing through the first resistor (R1) and
the voltage across R1.
3. Repeat the setup in figure 3 and record the Current as I2 and the Voltage as V2
on the data table. This is the flowing through the second resistor (R2) and the
voltage across R2.
Parallel Circuit Data Table
Trial 1
It
Trial 2
Vt
I1
Trial 3
V1
I2
V2
Data and Observations for Part A: Series Circuits
1. The voltage across the resistors is ____________ volts.
2. The Current flowing through the two resistors is _____________ amperes.
3. The resistance of the two resistors is ______________ ohms.
Conclusion for Part A: Series Circuits
Discuss your major results and answer the following questions:
1. When a circuit consists of resistors in series, the total resistance of the circuit is
equal to ____________________________
2. When a circuit consists of resistors in series, the sum of the voltage drops across the
individual resistors is equal to______________________
3. Write the equation for the current flowing through each resistor._________________
4. How do the terminal voltage and the voltages across each resistor
relate?____________________
5. What can we say about the current through a series circuit?____________________
Data and Observations for Part B: Parallel Circuits
1. The voltage across the resistors is ________________ volts.
2. The Current flowing through the parallel circuit is _______________ amperes.
3. The resistance of the two resistors in parallel is ___________________ ohms.
Conclusion for Part B: Parallel Circuits
Discuss your major results and answer the following questions:
1. When a circuit consists of resistors in parallel, the total resistance of the circuit is
equal to ______________________
.
2. When a circuit consists of resistors in series, the sum of the current flow through
each branch is equal to ________________________
.
3. Write the equation for the voltage across the circuit consisting of resistors in parallel.
4. How do the current leaving the battery and the current across each resistor relate?
5. What can we say about the voltage in a parallel circuit?
6. How can a resistance of 20 ohms be reduced to 5 ohms?
7. List three resistances that can be obtained by combining 100-ohm resistors in all
possible ways.