Honors Physics
2 Semester Review
Chapter 18 Basic Electric Circuits
nd
Terms
resistors
series
parallel
equivalent resistance
Kirchhoff’s loop theorem
Kirchhoff’s junction theorem
RC circuits
Tau (τ) time constant
concepts
Be able to find the equivalent resistance of a series of resistors
Be able to find the equivalent resistance of several parallel resistors
Be able to find the equivalent resistance of a combination of series and parallel resistors
Be able to state Kirchoff’s circuit rules
Using Kirchhoff’s circuit rules find the current in the conductors of multi-loop circuits.
Be able to explain the charging of capacitors in a RC circuit
o What effect would a larger capacitor have on the time constant in a RC circuit ?
 Explain
o What effect would a larger resistor have on the time constant in a RC circuit ?
 Explain
Problems
Resistances in Series, Parallel, and Series–Parallel Combinations
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9.
MC Which of the following quantities must be the same for resistors in series? (a) voltage, (b) current, (c)
power, (d) energy.
MC Which of the following quantities must be the same for resistors in parallel? (a) voltage, (b) current,
(c) power, (d) energy.
MC Two resistors (A and B) are connected in series to a 12-V battery. Resistor A has 9 V across it. Which
resistor has the least resistance? (a) A, (b) B, (c) both have the same, (d) can’t tell from the data given.
MC Two resistors (A and B) are connected in parallel to a 12-V battery. Resistor A has 2.0 A in it and the
total current in the battery is 3.0 A. Which resistor has the most resistance? (a) A, (b) B, (c) both have the
same, (d) can’t tell from the data given.
MC Two resistors (one with a resistance of 2.0 and the other with 6.0 resistance) are connected in
parallel to a battery. Which one produces the most joule heating? (a) 2.0 , (b) 6.0 , (c) both produce the
same, (d) can’t tell from the data given.
MC Two lightbulbs (bulb A has a rating of 100 W at 120 V and B has a rating of 60 W at 120 V) are
connected in series to a wall socket at 120 V. Which one produces the most light? (a) A, (b) B, (c) both
produce the same, (d) can’t tell from the data given.
CQ Are the voltage drops across resistors in series generally the same? If not, under what circumstance(s)
could they be the same?
CQ Are the currents in resistors in parallel generally the same? If not, under what circumstance(s) could
they be the same?
CQ If a large resistor and a small resistor are connected in series, will the effective resistance be closer in
value to that of the large resistance or the small one? What if they are connected in parallel?
11. CQ Three identical resistors are connected to a battery. Two are wired in parallel, and that combination is
followed in series by the third resistor. Which resistor(s) has (a) the largest current, (b) the largest voltage,
and (c) the largest power output? (a) third (b) third (c) third
13.  Three resistors that have values of 10 , 20 , and 30 , respectively, are to be connected. (a) How
should you connect them to get the maximum equivalent resistance, and what is this maximum value? (b)
How should you connect them to get the minimum equivalent resistance, and what is this minimum
value? (a) in series, 60 (b) in parallel, 5.5
16. IE  (a) In how many different ways can three 4.0- resistors, be wired: (1) three, (2) five, or (3) seven?
(b) Sketch the different ways you found in part (a) and determine the equivalent resistance for each. (a) (3)
seven (b) 1.3 , 2.0 , 2.7 , 4.0 , 6.0 , 8.0 , and 12 ; see ISM
17.  Three resistors with values of 5.0 , 10 , and 15 , respectively, are connected in series in a circuit with
a 9.0-V battery. (a) What is the total equivalent resistance? (b) What is the current in each resistor? (c) At
what rate is energy delivered to the 15- resistor? (a) 30 (b) 0.30 A (c) 1.4 W
26.  What is the equivalent resistance of the resistors in Fig.? 0.80
27.  What is the equivalent resistance between points A and B in Fig. ? 2.7
28.  What is the equivalent resistance of the arrangement of resistors shown in Fig. 18.27? 7.5
Kirchhoff’s Rules
43. MC You have a multiloop circuit with one battery. After leaving the battery, the current encounters a
junction into two wires. One wire carries 1.5 A and the other 1.0 A. What is the current in the battery? (a)
2.5 A, (b) 1.5 A, (c) 1.0 A, (d) 5.0 A, (e) can’t be determined from the given data.
46. MC You have a multiloop circuit with one battery that has a terminal voltage of 12 V. After leaving the
positive terminal of the battery, a short wire takes you to a junction where the current splits into three
wires. From that point until you return to the negative terminal of the battery, what can you say about the
sum of the voltages in each wire: (a) they total 12 V, (b) they total 12 V, (c) their magnitude is less than
12 V, or (d) their magnitude is greater than 12 V.
47. CQ Must the current in a battery (in a complete circuit) always travel from its negative terminal to its
positive terminal? Explain. If not, give an example. no, see ISM
RC Circuits
65. CQ Does charging a capacitor in an RC circuit to 25% its maximum value take longer or shorter than one
time constant? Explain. shorter, see ISM
66. CQ Explain why the current in a charging RC circuit decreases as the capacitor is being charged. charges
on capacitor resist more charges to be transferred
68.  A capacitor in a single-loop RC circuit is charged to 63% of its final voltage in 1.5 s. Find (a) the time
constant for the circuit and (b) the percentage of the circuit’s final voltage after 3.5 s. (a) 1.5 s (b) 90%
69. IE  In a flashing neon sign display, a certain time constant is desired. (a) To increase this time constant,
you should (1) increase the capacitance, (2) decrease the capacitance, or (3) eliminate the capacitor. Why?
(b) If a 2.0-s time constant is desired and you have a 1.0- F capacitor, what resistance should you use in
the circuit? (a) (1) increase the capacitance (b) 2.0 M