(a) J
(b) J
(c) JSection 4 - Electric potential
4.1 (a) Calculate the potential 1.00 m from an isolated proton. (b) Calculate the potential 1.00 m from an isolated electron. (c)
Which potential is greater? (d) Which potential has a greater magnitude?
(a) V
(b) V
(c) i. Near the proton
ii. Near the electron
iii. Potentials are equal
(d) i. Near the proton
ii. Near the electron
iii. Magnitudes are equal
4.2 In a science fiction story, a microscopic black hole is given an enormous positive charge by firing an un-neutralized ion drive
exhaust (consisting of positively charged xenon ions) into it for six months. The idea behind the charging process is to be able
to confine and manipulate this dangerous object with powerful electric fields. Suppose the charge on the black hole is 5740 C.
At what distance from it is the electric potential equal to 1.09e+3 V?
m
4.3 A positively charged, small region in a thundercloud creates an electric potential of 67.6 mV at ground level, 321 m below.
What is the charge of the region?
C
4.4 A nonconducting sphere of radius R = 5.00 cm contains a total charge of 4.25×10í^8 C, uniformly distributed throughout its
volume. What is the potential due to this charge distribution at a point at distance r (measured in meters) from the center of
the sphere, where r > R? Express your answer in terms of r. (Hint: According to a version of the shell theorem, the force
exerted by the sphere on a test charge at any external point is the same as if all the charge of the sphere were concentrated
at its center.)
382/(0.05+r)
382/r
382/(r-0.05)Section 6 - Electric potential difference
6.1 The negative (black) terminal of a 12 V automobile battery is grounded to the frame of a car. If we arbitrarily take the
automobile frame to be at an electric potential of 20 V, what is the electric potential of the positive (red) terminal of the
battery?
VSection 7 - Potential difference, electric potential energy and work
7.1 An electron with charge í1.60×10í^19 C moves a distance of 3.17 mm in the negative x direction in a uniform electric field of
125 N/C that points in the positive x direction. (a) How much work does the field do on the electron? (b) What is the change in
the potential energy of the electron? (c) Through what potential difference does the electron move?
(a) J
(b) J
(c) V
7.2 The electric potential difference across the cell membrane of a human cell is 0.080 V, with the higher potential being outside
the cell. In one cellular process a sodium ion Na+, with charge +e, is "pumped" through a channel in the membrane to be
ejected from the cell. (a) How much work must be done by the cell to eject the ion? (b) A candy bar contains 270 Calories, or
1.13×10^6 J of food energy. How many sodium ions could the cells of your body eject using the energy obtained in one candy
bar?
(a) J
(b) ions
7.3 A planet far, far away was impacted by a one-kilogram ball of pure "protonium" containing 6.00×10^26 protons, and nothing
else. This excess charge eventually distributed itself evenly through the planet, which had previously been electrically neutral.
(a) If the radius of the planet, like Earth's, is 6.37×10^6 m, what is the magnitude of the electric field at the planet's surface?(^454) Copyright 2007 Kinetic Books Co. Chapter 24 Problems