Simple Circuits (answer all questions in your lab book)
Answer questions using complete sentences that reflect the question, remember every line represents a wire.
PROCEDURE (Write answers in lab book. Use complete sentences that refer to the question.)
1. Obtain a bulb, (insulated) wire, and a battery. Find four DIFFERENT ways to light the bulb. Draw sketches
of the four successful ways AND ALSO four Unsuccessful ways to light the bulb. Use only one bulb, one
wire, and one battery. Do not use more than that for #1.
2.
Connect two batteries (3 V total) to a bulb using two wires. Observe its brightness. This is your indicator bulb “A”
which all other brightness will be compared to. Connect another bulb in SERIES using a wire between
bulb A and bulb B. The brightness of the bulb is an indication of the current (symbol for current is I)
through the bulb. Pay attention to LARGE DIFFERENCES in brightness.
A
a. Did the brightness of bulb A change when B was added in series? ( or no change)
b. Did the current through A change when B was added in series? ( or no change)
c. Compare the brightness of A to B with both in series.
d. Based on your observations, what can you conclude about the amount of current through A and
A
B connected in series?
B
Current is actually the amount of charge per second that moves through the battery (in this case) then
out into the circuit and (finally) back to the battery.
e. Can you visually tell the direction of current flow through the circuit? If yes, tell how.
f. Which of the following is/are kept constant in BOTH of these two circuits (one vs. two bulbs in series):
voltage supplied to circuit, current through each bulb, current through the battery.
If the resistance to current flow increases along the path of a bulb, the bulb gets dimmer. If the resistance decreases,
the bulb gets brighter.
g. What happens to the resistance to current flow when B is added in series to A? ( or no change)
h. How does the amount of current through the battery in a single-bulb circuit (A) compare with the current through
the battery in the series circuit (A and B)?
3.
Set up a new circuit, this time connecting two bulbs in PARALLEL. The terminals of the bulbs
should be connected together.
A
B
a. Did the brightness of bulb A change when B was added in parallel? ( or no change)
b. Did the current through A change when B was added in parallel? ( or no change)
c. Compare the brightness of A to B with both in parallel.
d. Based on your observations, what can you infer about the amount of current through each bulb connected in
parallel?
e. Describe the flow around the entire circuit. “Current flows through the battery, at the first junction it. . .” End
with the current flowing back into the battery.
f. Which of the following are kept constant in these two circuits (one vs. two bulbs in parallel):
voltage supplied to circuit, current through each bulb, current through battery.
g. What happens to the resistance to current flow when B is added in parallel to A? ( or no change)
h. What can you infer about the amount of current through the battery in a single-bulb circuit and the current
through the battery in the circuit with two identical bulbs connected in parallel?
i. Does the current through the battery appear to remain constant or to depend on the number of bulbs in a circuit
and how they are connected?
Simple Circuits (answer all questions in your lab book)
4.
Set up a series circuit with two bulbs (see below). Bulb A will be the indicator bulb. Add another bulb (C) in parallel
with bulb B as shown below. BEFORE you complete the circuit, predict the relative brightness of the bulbs. Record
your prediction. Close the connection.
a.
Based on your observations, what can you infer about the amount of current through bulb A (and hence through
the battery) when bulb C is added in parallel with bulb B? ( or no change)
b. What happens to the resistance to current flow through bulb A when bulb C is added parallel with bulb B?
( or no change)
c.
Devise a rule that tells how the current through the battery changes when bulbs are added in parallel.
d. Devise a rule that tells how the current through the battery changes when bulbs are added in series.
e.
Is the rule you devised for bulbs added in parallel consistent with the rule you devised for bulbs added in series?
EXPLAIN
A
A
B
5.
B
C
Consider the following dispute between two students.
A
I
B
C
II
Student #1: The current through the battery in each circuit is the same. In circuit II, the current from the battery is
divided between the bulbs B and C – so each bulb has half the current through it that bulb A in circuit I has
through it.
Student #2: We know the current through B and C in circuit II is the same as through bulb A in circuit I. That’s
because the bulbs are all about the same brightness – and bulbs that are equally bright have the same
current through them. So the flow through the battery in circuit II is more than that through the battery in
circuit I.
Do you agree with Student #1 or Student #2? Explain.
6.
Consider the following dispute between two students.
Student #1: Bulbs are resistors so adding bulbs to a circuit increases the total resistance. There is a bigger obstacle to
the current so less flows.
Student #2: Even though bulbs are considered to be resistors, adding them to a circuit may increase or decrease the
total resistance of the circuit. It all depends on how you add them.
Do you agree with Student #1 or Student #2? Explain.
Simple Circuits (answer all questions in your lab book)
7.
Two students are predicting the brightness of identical bulbs in the circuit below.
A
B
C
D
Student #1: All the current is through A. Then it divides between B and C so they will be equally dim, lots dimmer
than A. Then the current comes together again and it all goes through D. Bulb D will be the same
brightness as bulb A.
Student #2: I think D will be a lot dimmer than A; in fact, maybe it won’t light at all. Some of the current is used up at
A. Even more gets used up as the remaining current splits and goes to B and C. Maybe D will be bright
and A will be dim; it depends on the direction of the flow through the circuit. This would be a good test to
find the direction of the current.
Do you agree with Student #1 or Student #2? Explain.
8.
Identical bulbs are connected to identical batteries in the various circuits below.
a. Use your model and previous observations to rank all the bulbs (A - H) in order by brightness (use <, >, =).
If two bulbs have the same brightness, enclose the symbols in a circle.
b. Rank all the bulbs (A - H) in order of the amount of current flowing through each bulb. (use <, >, =).
If two bulbs have the same brightness, enclose the symbols in a circle.
c. Rank the circuits in order of the amount of current flowing through the battery (use <, >, =). EXPLAIN.
d. Rank the circuits in order of the obstacle to the flow of current presented by the various combinations of bulbs,
that is, rank them in order of the total resistance in each circuit (use <, >, =). EXPLAIN.
B
#1
A
#2
C
G
#3
D
E
#4
F
H