1.3 The electric field in the copper wire of a household circuit is oriented along the wire, so that it pushes electrons through the
circuit. (In alternating current, the direction of this electric field reverses 120 times a second.) A typical value for the field
strength is 0.00850 N/C. The charge of a mobile electron in the wire is í1.60×10í^19 C. What is the magnitude of the force that
the field exerts on the electron?
N
1.4 A hard rubber comb can be given a negative electric charge by rubbing it against a variety of materials, including human hair.
Suppose an atmospheric ion having a charge of +1.60×10í^19 C is resting at a point near the comb where the strength of the
field is 973 N/C. (a) What is the magnitude of the force that the field exerts on the ion? (b) Will the ion move toward the comb
or away from the comb?
(a) N
(b) i. Toward the comb
ii. Away from the comb
1.5 The surface of the drum of a laser printer is negatively charged, except in certain "print black" regions, such as letterforms,
that have been discharged by a laser beam. Negatively charged ink particles carrying a charge of 5.0 mC cling to the "print
black" areas but are repelled by an electric field elsewhere on the drum whose strength at the surface equals 120,000 N/C.
What is the magnitude of the repelling force felt by these particles?
NSection 2 - Electric fields and Coulomb’s law
2.1 Two friends are playing a version of proton golf where the hole is marked by a single proton. The first friend reads his meter,
and declares he has a field strength of 23.5 N/C. The second friend looks at her meter and realizes she is three times as far
away. What field strength does the second friend's meter read?
N/C
2.2 An ion harvester is scouring deep space for isolated xenon (Xe+) ions. A xenon ion is singly ionized, and has a charge of +e.
If the field meter reads 2.93eí7 N/C, how far away is it from the ion?
m
2.3 In a hydrogen atom in its lowest energy state, the single electron and the single proton are separated by a tiny distance called
the Bohr radius, 5.29×10í^11 m. The proton carries a charge e = 1.60×10í^19 C. (a) What is the strength of the electric field
generated by the proton at the Bohr-radius distance? (b) In what direction does the field point?
(a) N/C
(b) i. Towards the proton
ii. Away from the proton
2.4 A solid conducting sphere with a radius of 35.4 cm contains a total charge of 5.46 mC, evenly distributed over its surface. (a)
What is the direction of the electric field at its surface? (b) What is the strength of the electric field at its surface? Hint: use the
shell theorem, which states that when calculating an electrostatic force or field outside a charged sphere, the sphere can be
treated as though all of its charge resides at its center.
(a) i. Tangent to the surface
ii. Radially away from the center
iii. Radially toward the center
(b) N/CSection 5 - Interactive problem: fields and forces
5.1 Use the simulation in the first interactive problem in this section to answer the following questions. (a) Is the force on the test
charge greater where the field lines are closer together, or where they are farther apart? (b) What is the relationship between
the direction of the force and the field lines?
(a) i. Closer together
ii. Farther apart
iii. The force is the same all over
(b) i. The direction of the force is perpendicular to the field lines
ii. The direction of the force is tangent to the field lines
5.2 Use the simulation in the second interactive problem in this section to answer the following questions. (a) At a particular
location, how does the direction of the force exerted by the field on a positive charge differ from the force direction on a
negative charge? (b) How many times larger is the force on the +2q charge than on the +q charge?
(a) i. Directions are the same
ii. Directions are opposite
iii. Directions are perpendicular to each other(^432) Copyright 2007 Kinetic Books Co. Chapter 23 Problems