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LAB 5 Homework
Fundamentals of Circuits III: Voltage & Ohm’s Law
Question 1 In Activity 1.1 you observed the brightness of the light bulbs in Fig. 1(a) Fig. 1(c)
below.
(a) What were your observations regarding the brightness of bulbs B and C in Fig. 1(c) as
compared to the brightness of bulb A in Fig. 1(a)?
(b) What do you deduce about the quantitative relationship between the current in the twobulb, two-battery circuit as compared with that in the single-bulb, single-battery circuit?
(c) What happens to the overall resistance of the circuit as more bulbs are added in series?
S
S
S
+
B
B
−
+
+
A
−
−
+
C
C
−
(a)
(b)
(c)
Figure 1: Series circuits with (a) one battery and one bulb, (b) one battery and two bulbs and
(c) two batteries and two bulbs. (All batteries and all bulbs are identical.)
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Homework: Fundamentals of Circuits III: Voltage & Ohm’s Law
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Question 2 Three identical batteries are connected as in Fig. 2 below.
2
+
C
−
+
+
−
−
A
B
1
Figure 2: Three identical batteries. Two batteries (A and B) connected in parallel and a third
(C) connected in series with the combination of the first two.
If the potential difference across each individual battery is 1.5V, what is the difference in
potential between points 1 and 2? Explain your answer based on your observations from
Activity 1-2
Question 3 In Activity 2-1 you connected two light bulbs in parallel according to Fig. 3 below.
S
+
+
+
A
B
−
VP1
VP2
−
−
Figure 3: Voltage probes connected to measure the potential differences across bulbs A and B.
(a) In the axes below sketch your observations of voltage probes VP1 and VP2.
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Voltage 2 (V)
Voltage 1(V)
Homework: Fundamentals of Circuits III: Voltage & Ohm’s Law
Time (s)
(b) According to your observations what can you conclude regarding the difference of potential
between elements of circuits that are connected in parallel? Explain your answers based on
your graphs in (a)
Question 4 In the circuit below, the battery maintains a constant potential difference between
its terminals at points 1 and 2 (i.e., the internal resistance of the battery is considered negligible).
5
A
B
C
4
3
1
2
+
−
The three light bulbs, A, B and C are identical.
(a) How do the brightnesses of the three bulbs compare to each other? Explain your reasoning.
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Homework: Fundamentals of Circuits III: Voltage & Ohm’s Law
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(b) What happens to the brightness of each of the three bulbs when bulb A is unscrewed and
removed from its socket? Explain your reasoning.
(c) When A is unscrewed, what happens to the current through points 3,4 and 5? Explain
your reasoning.
(d) Bulb A is screwed back in. What happens to the brightness of each of the three bulbs when
bulb C is unscrewed and removed from its socket? Explain your reasoning.
(e) When C is unscrewed, what happens to the current through points 3,4 and 5? Explain
your reasoning.
Question 5 (a) State Ohm’s law in words.
(b) Does a resistor have a constant resistance? Explain. Is a resistor ohmic?
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Homework: Fundamentals of Circuits III: Voltage & Ohm’s Law
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Question 6 In the following circuits, tell which resistors are connected in series, which are
connected in parallel and which are neither in series nor parallel.
A
I
A
B
C
II
B
C
D
A
III
A
C
B
B
D
E
IV
C
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