AP Physics 1 Ch15 – 18 Homework
Ch15 HW#1 p573 4,5,6,7,8,17,22
4. A very small conducting sphere in air carries a charge of 5.0 picocoulombs and is 0.20m from another such sphere carrying
a charge Q. If each sphere experiences a mutual electrical repulsion of 20μN, find Q.
5. Two protons are fired directly at each other in a vacuum chamber. What is the force each expreiences the instant they are 1.0x10-14m
apart? (qproton = +1.6x10-19C)
6. Two point charges of +0.50μC are 0.10m apart. Determine the net electric force they experience in air.
7. Two equally charged small spheres repel each other with an electric force of 1.0N when 0.50m apart.
What is the charge on each sphere?
8. Two small spheres in a vacuum carrying charges of +1.00μC and –1.00μC are 1.00m apart, center-to-center.
What is the electrostatic force each experiences?
17. Three small negatively charged metal spheres in a vacuum are fixed on a horizontal straight line, the x-axis. One (-12.5μC) is at the
origin, another (-5.0μC) is at x=2.0m, and a third (-10.0μC) is 1.0m beyond that at x=3.0m.
Compute the net electric force on the last sphere due to the other two.
Ch15 HW#2 p573 22,23,24,27
22. Point charges of +1.0nC, +3.0nC, and –3.0nC are located, one each,
at the three corners of an equilateral triangle of side-length 30cm.
Find the net electrostatic force exerted on the 1.0-nC charge.
Assume the surrounding medium is a vacuum.
23. Four point charges are fixed at the corners of a rectangle in a vacuum.
Compute the net electric force on q1 .
24. Three very small spheres are located in a plane in air as follows:
q1 = +15μC at point (0,0), q2 = –20μC at (0,2), and q3 = +10μC
at point (2,2). Find the net force on q3.
27. Two 2.0g pith balls hang in air on cotton threads 50cm long
from a common point of support. The balls are then
equally charged and they spring apart, each making an angle of 10⁰
with the vertical. Find the magnitude of the charge on each ball.
Ch15 HW#3 p574+ 30,31,33,35,36,40,49
30. Determine the electric force acting on an electron placed in a uniform north-to-south E-field of 8.0x104 N/C in vacuum.
31. A test charge of +5.0nC placed at the origin of a coordinate system experiences a force of 4.0x10 -6 N in the positive y direction.
What is the electric field at this location? Assume the medium is a vacuum
33. A very small conducting sphere carrying a charge of –20nC is attached to a force gauge and lowered into a uniform electric field.
A force on 2.0nN due east keeps the sphere in equilibrium. Describe the E-field, assuming air is the medium.
35. A –40.0nC test charge is placed in a 2,000.0 N/C electric field pointing due west in a region of space. Describe the electrostatic force
the charge will experience.
36. A small positively charged object is placed, at rest, in a uniform electric field in a vacuum. Write an equation giving its speed v after
a time t in terms of mass m and charge q.
40. Two point charges of +10nC and –20nC lie on the x-axis at points x = 0 and x = +10m, respectively. Find the electric field on the
axis at the point x = +5.0m. Assume a vacuum.
49. An electron is placed in a uniform electric field of 1.5x10 4 N/C. Please determine its acceleration.
Ch15 HW#4 1 – 3
1. What is the strength of the electric field 0.5 m from a +2 C charge?
2. Two +2 C point charges are located 0.5 m from each other. Calculate the electric force between them. Is it attractive or repulsive?
3. Write a brief statement about the relationship between the equations used in #2 and #3.
Ch17 HW#1 p639 1,3,5,7,10,13,19,20
1. The moving nonconducting belt of a Van de Graaff generator carries 10μC of charge up to the metal sphere each
second. Determine the corresponding current.
3. If a quantity of singly sodium ions (Na+) equal to Avogadro’s number streams past a point in 1000 s, what is the current?
5. The starter motor in automobile is a small but powerful electrical device that “turns over” the main gasoline engine,
moving it through a cycle to get it started. Typically, it will draw about 180A from the battery for perhaps 2.0 s.
How much charge flow through the circuit?
7. A synchrotron accelerates protons up to nearly the speed of light, imparting energies to them of 500 MeV.
In the beam current is 1.0 mA, how many protons will hit a target in 0.10 s?
10. A portable tape recorder is powered by six 1.5-V AA-Cell in series. What is the operating voltage?
13. A battery is rated at 10 amp-hours. How much charge does that correspond to?
19. We wish to make up a panel of silicone solar cells that will provide at least 440 mA at 9.0 V when placed in
appropriately illuminated region. Given that each cell has an output of 22 mA at 0.45 V, design the panel.
20. A small cell has an emf of 0.80 V and can supply 10.0 mA under normal operating conditions. How should a battery
be constructed if it is to have an emf of 12.0 V and an operating current of 30.0 mA? How many cells will be needed?
Ch17 HW#2 p640 17,24, 26, 28, 29, 33
17. (Better copy on ppts)
24.
26.
28.
29.
33.
A 6.0-Ω resistor is placed across the terminals of a 12.0-V battery. How much current flows through the resistor?
Three 1.5-V cells are connected in series and the combo attached to a resistor. If 3.0A flows thru the resistor, what is its resistance?
A small high-torque variable-speed dc motor requires an input of 10 mA at 3.0 V. Determine the electrical resistance of the motor.
A 100-V electric heater draws 10 A. What is its resistance?
Six 1.5-V cells are connected in two strings, each of which has three cells in series. These two are then attached to each other
in parallel and put across a 90.0-Ω resistor. How much current flows through the resistor?
Ch17 HW#3 p640 25,31,34,36,38,42,43
25. A length of wire with a resistance of 150Ω is placed across the terminals of a battery
comprised of six 1.5-V cells in a series. How much current will it draw from the battery?
31. A wooden stick in contact with the metal sphere of a 100-kV Van de Graaff generator
carries out a current of 2.0μA down to ground. Calculate the stick’s resistance.
34. Figure P34 shows a variable resistance (total 100 Ω) across which is a voltage drop of 12V
supplied by a battery. What must be the resistance of that portion of the resister between
A and B (namely RAB) if the voltage VAB is to be: a. 12V
b. 6.0V
c. 3.0V
A
B
12V
36. A variable slidewire resistor with a total of 50 Ω is made by wrapping a single layer of 200 turns of varnished copper wire around
an insulating cylindrical core. When it carries a current of 3.0A, what is the voltage drop across each turn of wire?
38. Two 12-V batteries are connected with a positive terminal of one attached to the negative terminal of the other, the two remaining
terminals are then each attached to one of the terminals of a 600-Ω resistor, thereby forming a closed circuit. How much current
passes through each battery?
42. A nichrome wire with a cross-sectional area of 1.5 x 10-6 m2 is to be used as a heater. If the design calls for a 3.0Ω coil,
what length of wire will be needed?
43. A 5.0-m long wire has a cross-sectional area of 2.0 mm2 and a resistance of 40mΩ. Resistivity of the wire material?
CH17 HW#4 p640 64,66,68,69
64. What is the maximum current that should be passed through a 100-Ω, 10-W resistor?
66. A windmill with 6-ft propellers generates dc at 12 V. In a strong wind it will produce up to 200 W of electrical power,
which is fed to a 230-amp-hour battery. What’s the maximum current the windmill will deliver?
68. A light bulb operating at 110 V draws 1.82 A. Determine its resistance and the amount of power it draws.
69. A powerhouse near a waterfall has a large dc generator that produces electricity for a factory 0.50 mile away. The energy is
transmitted over two cables each with a resistance of 0.25 Ω/mile. Given that the factory requires 45 kW at a voltage 110 V
to run its equipment, what must be the output of the powerhouse?
Ch18 HW#1 p668 3,4,6,16,18,19,20
3. A D-cell with an emf of 1.50 V and an internal resistance of 0.05 Ω is placed in a circuit with several resisitors. The cell provides
0.50 A to the circuit. What is the terminal voltage of the cell?
4. A battery with a terminal voltage of 11.95 V when delivering 0.50A, has an internal resistance of 0.10 Ω. What is its emf?
6. A DC source with a terminal voltage of 100 V internally dissipates 40 W
as it delivers 2.0 A. What is its emf?
16. Two 30.0-Ω resistors are attached in series and then placed across the terminals of a 12.0-V battery having a negligible
internal resistance. How much current flows through the circuit?
18. Three 3.0-Ω resistors are connected in parallel and the combination is placed
across a battery that has a terminal voltage of 9.0 V. How much current flows through the battery?
19. Two 2.0-Ω resistors are in parallel. What is their equivalent resistance?
20. Three resistors with values of 2.0 Ω, 3.0 Ω, and 6.0 Ω are connected in parallel. What is the equivalent resistance?
Ch18 HW#2 p669 15,17,21,26,28,31,46
15. What is the current in the circuit of Fig. P15 before and after the wire
is clipped on at C and B? What happens to the 12-Ω bulb after the wire is attached?
17. Each lamp in Fig. P17 has a resistance of 20 Ω. How much current is drawn
from the battery before and after the wire is attached? How does the power
supplied to the circuit change when the wire is attached?
21. A portable generator in a field hospital produces dc at 100V. Five 100-W lamps
are attached in parallel and the string placed across the terminals of the generator.
How much current must the source provide for the lamps to operate as designed?
26. Determine the equivalent resistance of the circuit between points A and B
in Fig. P26.
28. Determine the equivalent resistance of the circuit between points A and B
in Fig. P28.
31. Determine the equivalent resistance of the circuit between points A and B
in Fig. P31.
P31
Ch18 HW#3 1,2, p670 24,46
1. a. Current from battery:____A
b. Current thru 10Ω:_____A
c. Current thru 20Ω: _____A
d. Current thru 30Ω: _____A
e. Current thru 5Ω: _____A
f. Power from battery: _____W
g. Power dissipated by 30Ω: _____W
2. a. Current from battery
b. Current thru 1Ω
c. Current thru 4Ω
d. Current thru 0.2Ω
e. Power from battery
f. Power dissipated by 4Ω
24. If in Fig. P24 the ideal ammeter reads 3.20 A,
what will the ideal voltmeter read?
46. (Modified) The battery in fig P46 has an emf of 9.0V
and internal resistance of 0.50 Ω.
a. What current does it supply?
b. What is the total power dissipated by the entire circuit?
c. What is the terminal voltage of the battery?
Ch18 HW#4 3, p670 33,34
3. a. Current from battery:____A b. Current thru 1Ω:_____A
c. Current thru 3Ω: _____A
d. Current thru 6Ω: _____A
e. Power from battery: _____W
f. Power dissipated by 3Ω: _____W
33. Figure P33 shows a portion of a circuit, the rest of which contains both
voltage sources and resistors. If the ammeter reads 9 A, what current
passes through each resistor shown?
34. Given that the ammeter in Fig. P34 reads 1.0 A, what is the emf
of the ideal DC source as indicated by the voltmeter.
Ch18 HW#5 4
4. What is the current thru R3? How much power is dissipated by R3?
Draw an ammeter symbol in a spot that reads the current through R 3.
Draw a voltmeter symbol in a spot that reads the voltage drop across R 3.
Ch18 HW#6 1 – 4
Ch18 HW#7 p670 71 – 74
Ch15 – 18 Rev
1. Calculate the electrical force between +10μC charge and +1μC test charge at 2m.
2. Calculate the magnitude of the electric field around a single +10μC charge at 2m.
3. A proton placed in a uniform E-field of 2x105 N/C pointing north. Find its acceleration.
4. At which bold, labeled location can a +1μC charge be placed,
such that the net force acting on it = zero.
What are the coordinates of that exact spot?
5. A beam of positrons carries 1.4 C past a point in a space in 2.0 sec.
What current does this correspond to?
6. A 1.0 m long wire of pure silver (ρ = 1.6 x 10-6 .m) has a resistance of 0.10 .
What is the radius of this wire?
7. The terminal voltage of a battery reads 8.9 V when a current of 0.10 A
runs through it. If a battery is rated at 9.0 V,
what is its internal resistance?
8. How much current through each 5  resistor?
How much power from the battery?
9. Point charges of +1.0 nC, +3.0 nC, and -3 nC are located one at each of the 3 corners
of an equilateral triangle of side length 30cm.
Find the net electrostatic force on the 1.0nC charge. Assume in a vacuum.
10. Determine the magnitude of an E-field if an electron placed it in a vacuum,
experiences force that will exactly cancel its weight at the Earth’s surface.
Free Response) A certain light bulb is designed to dissipate 6 watts when it is connected to a 12-volt source.
a) Calculate the resistance of the light bulb.
b) If the light bulb functions as designed and is lit continuously for 30 days, how much energy is used?
Be sure to indicate the unit in your answer.
The 6-watt, 12-volt bulb is connected to a circuit with 1500-watt, 120-volt toaster; an adjustable resistor; and a 120-volt power
supply. The circuit is designed such that the bulb and the toaster operate at the given values and, if the light bulb fails, the toaster
will still function at these values.
c) On the diagram, draw in wires connecting the components shown to make a complete circuit that will function as described above.