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Honors Physics: Unit 9
Names: ________________________________
Circuit Lab
Record your responses to the following on the answer sheet provided. One sheet per lab group.
1.
2.
3.
In the circuits to the right, the batteries and bulbs are identical, and
conventional current flows clockwise as shown. The unknown
elements “X” (another bulb perhaps) are identical to each other.
Explain your answers to the following in terms of our scientific
model of circuits.
A)
How would the brightness of the two bulbs compare?
B)
How does the current in the bulb compare to the current in
element X in each case?
X
X
In the circuits to the right, the batteries and bulbs are identical, and
conventional current flows clockwise as shown. The unknown
elements X and Y are different. It is observed that the bulb on the
left is brighter than the bulb on the right. Explain your answers to
the following in terms of our scientific model of circuits.
A)
How does the resistance of X compare to the resistance of Y?
B)
How does the current in the battery on the left compare to the
current in the battery on the right?
Predict the relative brightness of
bulbs B1, B2, and B3, in the circuits
shown to the right. Explain your
ranking based on your answer to
question 2 above. (Hint: In each of
the three circuits, the combination
of bulbs on the right side is like the
unknown elements X and Y in the
circuits in question 2. How do their
resistances compare?)
X
Y
B
B
B
1
2
3
Notes for the remainder of the lab:
You will be asked to make predictions about some circuits, and then set them up and make measurements of
current and voltage. Be careful to observe the polarity of the ammeter and the voltmeter, and not to overload
either meter. It is good practice to very briefly touch a contact to complete the circuit while observing the meter
needle. If the needle starts advancing to the left, its polarity is reversed.
None of these circuits should be left on for longer than it takes to make measurements. When you’re not making
observations or measurements, open the circuit.
Instead of a battery as a source of emf, you will use a DC power plug, but we will still refer to it as “the battery”.
Use the C-clamp to clamp the circuit board to the edge of the table. Connect the white wire from the DC power
plug to the spring labeled “–” and the black wire to the spring labeled “+”. Then plug the other end into the floor
outlet.
A
4.
Set up the single-bulb circuit as shown to the right. Measure the potential difference
across the battery and the potential difference across the bulb. Measure the current
at points A and B. As always, record your measurements with the proper units.
B
5.
Set up the two-bulb series circuit as shown to the right.
C
A)
B)
C)
D)
6.
Predict the ranking of the currents IC, ID, IE, and IA (from the previous circuit),
from largest to smallest. Explain your ranking based on our scientific model.
Measure the potential difference across the battery and each bulb, and measure the
currents IC, ID, and IE,.
D
2
How does the potential difference across the battery in this circuit compare to the
potential difference across the battery in the circuit from #4?
E
Predict what the voltmeter would read if it were connected to measure the potential difference across the
two series bulbs together. Explain your answer in terms of what you observed in #4.
Set up the two-bulb parallel circuit as shown to the right. A)
1
F
Predict the ranking of the currents IF, IG, IH, IJ, and IA (from the circuit in
#4), from largest to smallest. Explain your ranking based on our scientific
model.
G
1
2
J
7.
H
B)
Measure the potential difference across the battery and each bulb, and
measure the currents IF, IG, IH and IJ,.
C)
How does the potential difference across the battery in this circuit compare to the potential difference across
the battery in the circuit from #4?
D)
How does the current through the battery in this circuit compare to the current in the battery in the circuit
from #4?
Set up the three-bulb circuit as shown to the right. K
A) Predict the ranking of the potential differences across the battery and each bulb.
Explain your prediction.
B)
C)
8.
Predict the ranking of the currents IK, IL, IM, and IA from the circuit in #4, from
largest to smallest. Explain your prediction.
L
2
Measure the potential difference across the battery and each of the three bulbs,
and measure the currents.
Set up the three-bulb circuit as shown to the right. A)
1
Predict the ranking of the potential differences across the battery and each
bulb. Explain your prediction.
B)
Predict the ranking of the currents IN, IO, IP, and IA from the circuit in #4,
from largest to smallest. Explain your prediction.
C)
Measure the potential difference across the battery and the three bulbs, and
measure the currents.
3
M
N
1
O
2
3
P
9.
Consider the circuit to the right, but do not set up the circuit until #12.
A)
1
Predict the ranking of the brightness of the four bulbs. Explain your reasoning.
2
3
DO NOT MOVE ON UNTIL YOU MAKE YOUR PREDICTION
B)
If the resistance of each bulb is R, calculate the total resistance of the circuit in
terms of R.
Show your work on the answer sheet.
4
10. A wire is now added to the circuit from #9 as shown to the right. A)
Calculate the total resistance of the circuit in terms of R, the resistance of each
bulb, showing your work on the answer sheet.
B)
Predict how the brightness of each bulb will change (brighter, dimmer or the
same) when the wire is added, as compared to the bulbs in the circuit in #9.
Check the appropriate box, and explain your reasoning, showing any
calculations you make.
1
2
3
4
DO NOT MOVE ON UNTIL YOU MAKE YOUR PREDICTION
11. The wire is now removed to restore the circuit in #9. Then bulb 3 is unscrewed as
shown to the right. A)
B)
Calculate the total resistance of the circuit in terms of R, the resistance of each
bulb.
Predict how the brightness of each bulb will change (brighter, dimmer or the
same as compared to the bulbs in the circuit in #9) when the bulb is unscrewed.
Check the appropriate box, and explain your reasoning, showing any calculations
you make.
1
2
4
DO NOT MOVE ON UNTIL YOU MAKE YOUR PREDICTION
12.
A)
Set up the circuit from #9 now and record the actual ranking of the brightness of the bulbs.
B)
Connect a wire across bulb 3 and record the new ranking of the brightness of the bulbs.
C)
Disconnect the wire and unscrew bulb 3. Record the new ranking of brightness of the bulbs.
D)
Record the actual change in brightness of each bulb (compared with circuit #9) when the wire is added
across bulb 3.
E)
Record the actual change in brightness of each bulb (compared with circuit #9) when bulb 3 is removed.
In completing this lab, ensure that you have carefully written your predictions and your explanations. You will not
be counted off for inaccurate predictions unless your explanations for your predictions are incomplete.
If your prediction is correct, leave it as it is. If it is incorrect, please correct it WITHOUT ERASING and
indicate where your group was wrong in your explanation.