Download Series and Parallel Lab Name:

ep3/04
Series and Parallel Lab
Name: ______________________
Partners: _______________________________________
Date: __________
Period: ________
Purpose: Discover some of the behaviors of series and parallel circuits.
At different tables around the room, different circuits are set up, some with light bulbs and some with electronic
resistors. You are to go to each table, rotating every 10 minutes, and, following instructions below, draw
diagrams and record the appropriate data.
Do NOT adjust the power supply to make the bulbs brighter since you might burn them out by accident. If the
bulbs are not lit, check to see that they are screwed in firmly and that the switch in the middle of the power
supply is on. Never connect the wires that come out of a power supply directly to each other. This causes
damage.
On a separate piece of paper, title the paper with the label for the table and draw a large circuit diagram for the
circuit at your table. Use these symbols for the various components making up each circuit. Leave plenty of
room above and below each symbol to write comments. Use this same paper to record other data in a data table
and observations and the answers to the first several questions. Use a new paper to do the diagram and data for
the next table. To see the variety and amount of data you will be recording, read the instructions up to
ANALYSIS before starting.
Power supply or battery, with wires leading in and out.
Resistor, with wires
Light bulb
A
Ammeter
V
Voltmeter
Note that you should simplify the paths of the wires from one object to the next. If the wire bends in a loop, you
don’t have to duplicate this bend on your diagram, unless it helps to simplify the diagram. Your VIR lab has a
sample. Hint: The word “series” implies things lined up one after the other, so draw them that way. The word
“parallel” implies several different things that lie side by side, parallel to each other, so draw them that way.
Don’t be fooled by the way they are sitting. Look at the pathways the current has to follow after it comes out of
the power supply, goes through the circuit, then reenters the power supply. Ignore voltmeters at first, draw your
circuit without them, then add their symbols to the circuit after you are sure of the rest. To make it easier to
interpret later, draw all of the components on vertical and horizontal axis (i.e. square off your diagram).
You will turn in ONE copy of these sheets per team, along with one copy of this lab. EVERYONE on the team
is responsible to see everything is done properly! You should draw at least one of each setup in your lab book.
1.
Label the light bulbs or resistors #1, #2, #3, etc. Your lab grade will be partly based on the CLARITY of
the diagram so neatness counts here.
2.
Record the voltage, resistance (calculated), and current for every resistor and light bulb, as well as the
TOTAL current, resistance (calculated), and voltage. Remember to use the scale on the meter that
corresponds to the post the wire is hooked to. MEASURE THEM! Don’t just calculate what they ‘should’
be (that’s part 3). Do NOT disconnect the circuit in order to measure the total voltage. It will throw off your
values.
3.
Now calculate the total voltage, resistance, and total current. Compare those calculations to the
MEASURED values from part 2. For Parallel Circuits, calculate the % error for Current. For Series
Circuits, calculate the % error for Voltages. For Complex Circuits, calculate the % error for both.
4.
If you have light bulbs, record whether all are all equally bright OR all equally dim OR whether some
are bright and others dim. Label the bulbs in your diagram which are bright or dim, or dimmer, etc. Switch
places between two bulbs of different brightness to see if position has anything to do with brightness.
REMEMBER to move the bulbs back to their original positions ! ! !
5.
IF there are bulbs in a circuit, PARTLY unscrew each bulb, one at a time, and record which bulbs stay on
and which bulbs go out. I will leave it to you to develop a coherent data table to record this in. Make sure
that, after unscrewing a bulb and observing, you screw it back in. Don’t mix which bulbs go with which
sockets. IGNORE minor brightness changes.
6.
If there are resistors instead of bulbs in the circuit, record the resistance value of each resistor next to its
symbol in your diagram. The resistor values are typically between 250 Ω and 1 K Ω (that is 250 ohms and
1000 ohms)
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ANALYSIS: Ammeters measure electrical CURRENT (symbol I ) the rate at which charges move, with units
of AMPS (symbol A ) or milliamps (symbol mA ).
7.
Charges are never created or destroyed. Identify a case (which lab table setup) where current (moving
charges) from different pathways, that went through different light bulbs or resistors, seems to be coming
together. Describe what you think is happening to the current AND Justify with data.
8.
Identify a case (which lab table setup) where the current that goes into a light bulb at some point has
nowhere else to go but some other light bulb. Describe what you think is happening to the moving charges
AND Justify with data. (I am being deliberately vague, you should be more specific.)
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Voltmeters measure VOLTAGE (symbol V ), the change in electric energy per coulomb of charge, with
units of VOLTS (symbol V ).
An individual charge must use some of its energy to get through each part of the circuit it travels through
and the total energy used up must be the sum of each separate energy loss. However, it might be possible,
in some circuits, for a charge to bypass part of the circuit and thus lose no energy in this part. Finally, each
coulomb of charge starts out with the same amount of energy and each loses ALL of its energy by the time
it has finished going through the circuit. Remember, Voltage reading = energy loss per coulomb.
9.
Identify a case where the charges lose some energy in the first light bulb or resistor they go through, some
in the second, etc. and all these losses add up to the total loss for the entire circuit. Describe where you
think the energy is lost by the charges AND Justify with data.
10. Identify a case where a given charge will lose some energy in one light bulb but not in another.
where you think the energy is lost by the charges AND Justify with data.
Describe
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The remaining questions should be answered on this sheet, one copy for each team.
11. In a pure series circuit, the current in the first part of the circuit is
in the second part of the circuit.
the same / different
from the current
12. In a pure series circuit, the voltage drop (∆V) for the entire circuit, measured by the voltmeter that samples
the beginning and end of the circuit, is equal to the sum / difference of the voltage drops for the
separate parts of the circuit.
13. In a pure parallel circuit, the total current, measured where all the parallel branches come together, is equal
to the ____________ of the currents in the separate branches.
14. In a pure parallel circuit, the TOTAL voltage drop for each branch is
total voltage drop for any other branch.
the same as / different from
the
15. In a pure series circuit, when you unscrew a bulb (stopping the current from moving through that bulb),
does this stop the current from moving through the other bulbs? Yes / No
What is your evidence?
Does it matter which bulb you unscrew?
Yes / No
16. In a pure parallel circuit, when you unscrew a bulb (which stops the current from moving through the bulb),
does this stop the current from moving through the other bulbs? Yes / No
What is your evidence?
17. If you attach a voltmeter to each end of a single wire, the voltage reading should be zero. Knowing that
voltmeters measure energy change per charge, why is this reading zero? AND what does this say about
the wire’s Resistance?
18. Find a combo circuit in which the bulbs are not all of equal brightness. Show a data table HERE listing the
current (I), voltage (V), Relative brightness, and the Power for each bulb ( P = IV ). Compare the
brightness with the current, voltage, and power and describe which of these is the best predictor of which
bulb is brightest.