Problem Set 3
Due: see website for due date
Chapter 20: Circuits
Questions: A, B, C, 12
Problems: 10, 12, 30, 47, 50, 67, 68, 70
Question A: The wires ae all made of the same material; the length and radius of each
wire is noted. Rank in order, from largest to smallest, the resistances R1 to R5 of these
wires. Explain.
Question B: The circuit has two resistors, with R1 > R2. (a) Which resistor dissipates the
larger amount of power if the resistors are in series? (b) In parallel? Explain.
Question C: The four bulbs shown are identical. Rank the bulbs from
brightest to dimmest. Explain.
Q20.12: In the following three arrangements each resistor has the same
resistance R. Rank the equivalent resistances of the arrangements in descending order
(largest first).
(a) A, B, C; (b) B, A, C; (c) B, C, A; (d) A, C, B; (e) C, B, A
P20.10: The resistance and the magnitude
of the current depend on the path that the
current takes. The drawing shows three
situations in which the current takes
different paths through a piece of material.
Each of the rectangular pieces is made
from a material whose resistivity is ρ =
1.50×10-2 Ω∙m, and the unit of length in the drawing is L0 = 5.00 cm. Each piece of
material is connected to a 3.00-V battery. Find (a) the resistance and (b) the current in
each case. Answer: (0.600, 0.0375, 0.150) Ω; (5.00, 80.0, 20.0) A
P20.12: A cylindrical wire has a length of 2.80 m and a radius of 1.03 mm. It carries a
current of 1.35 A, when a voltage of 0.0320 V is applied across the ends of the wire.
From what material in Table 20.1 (see end of document for table) is the wire made?
Answer: 2.82×10-8 Ω∙m
P20.30: A piece of Nichrome wire has a radius of 6.5 ×10-4 m. It is used in a laboratory
to make a heater that uses 4.00×102 W of power when connected to a voltage source of
120 V. Ignoring the effect of temperature on resistance, estimate the necessary length of
wire. Answer: 50 m
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P20.47: Three resistors are connected in series across a battery. The value of each
resistance and its maximum power rating are as follows: 2.0 Ω and 4.0 W, 12.0 Ω and
10.0 W, and 3.0 Ω and 5.0 W. (a) What is the greatest voltage that the battery can have
without one of the resistors burning up? (b) How much power does the battery deliver to
the circuit in (a)? Answer: 15.5 V, 14.2 W
P20.50: A coffee-maker (14 Ω) and a toaster (19 Ω) are connected in parallel to the
same 120-V outlet in a kitchen. How much total power is supplied to the two appliances
when both are turned on? Answer: 1800 W
P20.67: Find the equivalent resistance between the points
A and B in the drawing.
Answer: 42Ω
P20.68: Each resistor in the three circuits in the
drawing has the same resistance R, and the
batteries have the same voltage V. The values
for R and V are 9.0 Ω and 6.0 V, respectively.
Determine the total power delivered by the
battery in each of the three circuits. Answer:
(4.00, 2.00, 8.00) W
P20.70: Determine the power supplied to each of the resistors in the
drawing. Answer: (11.1, 2.78, 2.78) W
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