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Quiz 5 (PHYS262, Summer 2001)

August 15, 2001

Figure 1 shows two point charges with charge $q$ at distances $d$ from a midpoint $P$. What is the total electric field at point $P$? ( $k_e = {1\over 4\pi \epsilon_0}$)

(a) $k_e q/d^2$ (b) $2k_e q/d^2$ (c) 0 (d) $k_e q/2d^2$ (e) None of the above

Figure 2 shows the electric field lines of two point charges of magnitude $q$ and opposite sign (dipole). With the same convention, what is the correct configuration of electric field lines of an isolated point charge $q$?

Figure 1: Prob 1
\centerline {\psfig{file=Q5-1.eps,
Figure 2: Prob 2
\centerline {\psfig{file=Q5-2.eps,

Figure 3: Prob 2
\centerline {\psfig{file=Q5-2a.eps,

A cube of size $L\times L\times L$ contains two point charges inside, with equal magnitude but with opposite sign ($q$ and $-q$). What is the net electric field flux through the surface of the cube?

(a) $q/\epsilon_0$ (b) 0 (c) $2q/\epsilon_0$ (d) $-q/\epsilon_0$ (e) Not enough information

Which one of the following statements about conductors in electrostatic equilibrium is FALSE?

The electric field is zero everywhere inside the conductor.
If an isolated conductor carries a charge, the charge resides on its surface.
The electric field just outside a charged conductor is perpendicular to the surface of the conductor and has a magnitude $\sigma /\epsilon_0$, where $\sigma $ is the surface charge density at that point.
On an irregularly shaped conductor, the surface charge density is greatest at locations where the radius of curvature of the surface is smallest.
None of the above.

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Hyok-Jon Kwon