The direction of an electric field is the direction of the force that it would exert on?1. a neutron2. an electron3. a protonExplain

A large charge +Q and a small charge q are a short distance apart. How do the electric forces on each charge compare? Is this comparison described by another physical law? (Hint: See Chapter 3.4.)

In the Millikan oil-drop experiment illustrated in Figure 15.21, an atomizer (a sprayer with a fine nozzle) is used to introduce many tiny droplets of oil between two oppositely charged parallel metal plates. Some of the droplets pick up one or more excess electrons. The charge on the plates is adjusted so that the electric force on the excess electrons exactly balances the weight of the droplet. The idea is to look for a droplet dial has the smallest electric force and assume it has only one excess electron. This strategy lets the observer measure the charge on the electron. Suppose we are using an electric field of 3 104 N/C. The charge on one electron is about 1.6 1019 C. Estimate the radius of an oil drop of density 858 kg/m5 for which its weight could be balanced by the electric force of this field on one electron. (Problem 42 is courtesy of E.F. Redish. For more problems of this type, visit www.physics.umd.cdu/pcrg/.)

What is the magnitude and direction of the force exerted on a 3.50 /C charge by a 250 N/C electric field that points due east?

(a) Common transparent tape becomes charged when pulled from a dispenser. If one piece is placed above another, the repulsive force can be great enough to support the top piece’s weight. Assuming equal point charges (only an approximation), calculate the magnitude of the charge if electrostatic force is great enough to support the weight of a mg piece of tape held 1.00 cm above another. (b) Discuss whether the magnitude of this charge is consistent with what is typical of static electricity.

Integrated Concepts (a) In Figure 18.59, four equal charges q lie on the corners of a square. A fifth charge Q is on a mass m directly above the center of the square, at a height equal to the length d of one side of the square. Determine the magnitude of q in terms of Q. m, and d, if the Coulomb force is to equal the weight of m. (b) Is this equilibrium stable or unstable? Discuss.

Calculate the electric field of an infinite line charge, throughout space.

What is the magnitude and direction of an electric field that exerts a 2.0010-5 N upward force on a -1.75 C charge?

Compare and contrast the Coulomb force field and the electric field. To do this, make a list of five properties for the Coulomb force field analogous to the five properties listed for electric field lines. Compare each item in your list of Coulomb force field properties with those of the electric field—are they the same or different? (For example, electric field lines cannot cross. Is the same true for Coulomb field lines?)

Suppose someone tells you that rubbing quartz with cotton cloth produces a third kind of charge on the quartz. Describe what you might do to test this claim.