Chapter 24: Q. 5 (page 682)
The electric field is constant over each face of the cube shown in FIGURE EX24.5. Does the box contain positive charge, negative charge, or no charge? Explain.

Short Answer
The charge of the box is postive
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Chapter 24: Q. 5 (page 682)
The electric field is constant over each face of the cube shown in FIGURE EX24.5. Does the box contain positive charge, negative charge, or no charge? Explain.

The charge of the box is postive
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FIGUREshows three charges. Draw these charges on your paper four times. Then draw two-dimensional cross sections of three-dimensional closed surfaces through which the electric flux is (a) , (b) , (c) , and (d) .

The charged balloon in FIGURE Q24.7 expands as it is blown up, increasing in size from the initial to final diameters shown. Do the electric field strengths at points 1, 2, and 3 increase, decrease, or stay the same? Explain your reasoning for each.

A sphere of radius has total charge . The volume charge Calc density role="math" localid="1648722354966" within the sphere is , where is a constant to be determined.
a. The charge within a small volume is . The integral of over the entire volume of the sphere is the total charge. Use this fact to determine the constant in terms of and .
Hint: Let be a spherical shell of radius and thickness. What is the volume of such a shell?
b. Use Gauss's law to find an expression for the electric field strength inside the sphere, , in terms of and.
c. Does your expression have the expected value at the surface, ? Explain.
The electric field must be zero inside a conductor in electrostatic equilibrium, but not inside an insulator. It turns out that we can still apply Gauss's law to a Gaussian surface that is entirely within an insulator by replacing the right-hand side of Gauss's law, , with , where is the permittivity of the material. (Technically, is called the vacuum permittivity.) Suppose that a point charge is surrounded by a thin, -diameter spherical rubber shell and that the electric field strength inside the rubber shell is . What is the permittivity of rubber
The two spheres in FIGURE Q24.8 on the next page surround equal charges. Three students are discussing the situation.
Student 1: The fluxes through spheres A and B are equal because they enclose equal charges.
Student 2: But the electric field on sphere B is weaker than the electric field on sphere A. The flux depends on the electric field strength, so the flux through A is larger than the flux through B.
Student 3: I thought we learned that flux was about surface area. Sphere B is larger than sphere A, so I think the flux through B is larger than the flux through A.
Which of these students, if any, do you agree with? Explain.

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