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4B PHYSICS Chapter 23 23.3 A small metal sphere, carrying a net charge of q1 = -2.80 C, is held in a stationary position by insulating supports. A second small metal sphere, with a net charge of q2 = -7.80 C and mass 1.50 g, is projected toward q1. When the two spheres are 0.800 m apart, q2 is moving toward q1 with speed 22.0 m/s (Fig. 23.28). Assume that the two spheres can be treated as point charges. You can ignore the force of gravity. a) What is the speed of q2 when the spheres are 0.400 m apart? b) How close does q2 get to q1? Fig. 23.28 23.6 Three equal 1.20-C point charges are placed at the corners of an equilateral triangle whose sides are 0.500 m. What is the potential energy of the system? (Take as zero the potential energy of the three charges when they are infinitely far apart.) 23.16 A particle with a charge of +4.20 nC is in a uniform electric field E directed to the left. It is released from rest and moves to the left; after it has moved 6.00 cm, its kinetic energy is found to be +1.5010-6 J. a) What work was done by the electric field? b) What is the potential of the starting point with respect to the end point? c) What is the magnitude of E? 23.22 Two positive point charges, each of magnitude q, are fixed on the y-axis at the points y = +a and = y -a. Take the potential to be zero at an infinite distance from the charges. a) Show the positions of the charges in a diagram. b) What is the potential V0 at the origin? c) Show that the potential at any point on the x-axis is 1 2q . d) Graph the potential on the x-axis as a function of x over V= 4 0 a 2 + x 2 the range from x = -4a to x = +4a. e) What is the potential when x >> a? Explain why this result is obtained. 23.38 Two large parallel conducting plates carrying opposite charges of equal magnitude are separated by 2.20 cm. a) If the surface charge density for each plate has magnitude 47.0 nC/m2, what is the magnitude of E in the region between the plates? b) What is the potential difference between the two plates? c) If the separation between the plates is doubled while the surface charge density is kept constant at the value in part (a), what happens to the magnitude of the electric field and to the potential difference? 23.43 The potential is given by V = 0 for z < 0, V = Cz for 0 < z < d, and V = Cd for z > d, where C and d are positive constants. The potential does not depend on x or y. a) Find the electric field (magnitude and direction) at all points. b) What charge distribution could be the source of this field? Explain. ... View Full Document