1. Discuss pros and cons of a lightning rod being grounded versus simply being attached to a building.
2. Using the symmetry of the arrangement, show that the net Coulomb force on the charge qq at the center
of the square below (Figure 1) is zero if the charges on the four corners are exactly equal.
3. (a) Using the symmetry of the arrangement, show that the electric field at the center of the square
in Figure 1 is zero if the charges on the four corners are exactly equal. (b) Show that this is also true for any
combination of charges in which qa=qbqa=qb and qb=qcqb=qc
4. (a) What is the direction of the total Coulomb force on qq in Figure 1 if qq is negative, qa=qcqa=qc and
both are negative, and qb=qcqb=qc and both are positive? (b) What is the direction of the electric field at the
center of the square in this situation?
5. Considering Figure 1, suppose that qa=qdqa=qd and qb=qcqb=qc. First show that qq is in static
equilibrium. (You may neglect the gravitational force.) Then discuss whether the equilibrium is stable or
unstable, noting that this may depend on the signs of the charges and the direction of displacement
of qq from the center of the square.
6. If qa=0qa=0 in Figure 1, under what conditions will there be no net Coulomb force on qq?
7. In regions of low humidity, one develops a special “grip” when opening car doors, or touching metal door
knobs. This involves placing as much of the hand on the device as possible, not just the ends of one's fingers.
Discuss the induced charge and explain why this is done.
8. Discuss what would happen if a
the capacitor plates.
9. Discuss how the energy stored in an empty but charged capacitor changes when a dielectric is inserted if
(a) the capacitor is isolated so that its charge does not change; (b) the capacitor remains connected to a
battery so that the potential difference between its plates does not change.
10. Voltage is the common word for potential difference. Which term is more descriptive, voltage or potential
difference?
11. If the voltage between two points is zero, can a test charge be moved between them with zero net work
being done? Can this necessarily be done without exerting a force? Explain.
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