24. Electric Force & Field; Gauss' Law

A charge Q is transferred from an initially uncharged plastic ball to an identical ball 21 cm away. The force of attraction is then 17 mN. How many electrons were transferred from one ball to the other?

Estimate the net force between the CO group and the HN group shown in Fig. 21–72. The C and O have charges ± 0.40e, and the H and N have charges ±0.20e, where e = 1.6 x 10⁻¹⁹ C. [Hint: Do not include the “internal” forces between C and O, or between H and N.]

A large electroscope is made with “leaves” that are 66-cm-long wires with tiny 21-g spheres at the ends. When charged, nearly all the charge resides on the spheres. If the wires each make a 26° angle with the vertical (Fig. 21–58), what total charge Q must have been applied to the electroscope? Ignore the mass of the wires.

3.5×10¹⁰ electrons are added to a plastic rod by rubbing it with wool. What is the charge on the rod?

A point charge ( m = 1.5 gram) at the end of an insulating cord of length 55 cm is observed to be in equilibrium in a uniform horizontal electric field of 9500 N/C, when the pendulum’s position is as shown in Fig. 21–79, with the charge 12 cm above the lowest (vertical) position. If the field points to the right in Fig. 21–79, determine the magnitude and sign of the point charge.