CALC Self-Energy of a Sphere of Charge . A solid sphere of radius R contains a total charge Q distributed uniformly throughout its volume. Find the energy needed to assemble this charge by bringing infinitesimal charges from far away. This energy is called the “self-energy” of the charge distribution. (Hint: After you have assembled a charge q in a sphere of radius r , how much energy would it take to add a spherical shell of thickness dr having charge dq ? Then integrate to get the total energy.)
CALC Self-Energy of a Sphere of Charge . A solid sphere of radius R contains a total charge Q distributed uniformly throughout its volume. Find the energy needed to assemble this charge by bringing infinitesimal charges from far away. This energy is called the “self-energy” of the charge distribution. (Hint: After you have assembled a charge q in a sphere of radius r , how much energy would it take to add a spherical shell of thickness dr having charge dq ? Then integrate to get the total energy.)
CALC Self-Energy of a Sphere of Charge. A solid sphere of radius R contains a total charge Q distributed uniformly throughout its volume. Find the energy needed to assemble this charge by bringing infinitesimal charges from far away. This energy is called the “self-energy” of the charge distribution. (Hint: After you have assembled a charge q in a sphere of radius r, how much energy would it take to add a spherical shell of thickness dr having charge dq? Then integrate to get the total energy.)
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A charge of -8.5 nC is uniformly distributed around a thin plastic ring lying in a yz plane with the ring center at the origin. A -5.0 pC point charge is located on the x
axis at x = 3.8 m. For a ring radius of 1.2 m, how much work must an external force do on the point charge to move it to the origin?
Number
0.00000008728
Units
the tolerance is +/-5%
Consider a cube made up of eight charges, each with equal
magnitude q but alternating sign as shown in the figure on
the right. This assembly is called an electric octopole, and
is also the basis for simple cubic crystal lattices formed of
opposite ions, such as NaCl (table salt). At this scale we may
neglect gravity.
a) What's the potential energy Udip required to assemble just
two opposite charges into a single edge of this cube? This
forms an electric dipole. (Hint: It doesn't take any energy to
"assemble" the first charge.)
+9
+9 d
b) What's the potential energy Uquad required to assemble
four charges into a single face of this cube? This forms an electric quadrupole.
+9
-9
+9
c) What's the potential energy Uoet required to assemble all eight charges into the octopole? (Hint: For
a cube there are a lot of pairings between charges, specifically (9) = 28, comprised of the shown edges, as
well as several diagonals. Instead of adding the contribution to the potential for bringing in…
A charge per unit length given byd = 2.40 µC/m is distributed uniformly along the circumference of a circle with a radius of 25.0 cm.
How much external energy is required to bring a charge of 35.0 µC from infinity to the center of the circle? (answer in Joules)
Chapter 23 Solutions
University Physics with Modern Physics, Volume 2 (Chs. 21-37); Mastering Physics with Pearson eText -- ValuePack Access Card (14th Edition)
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