3) A very small ball of mass 0.60 g has a charge of 8.0 uC. The ball is suspended from a vertical string in an electric field of 300 N/C in a downward direction. What is the tension in the string if the charge on the ball is (a) positive (b) negative    Answer key (a) 8.3 mN; (b) 3.5 mN

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= 32.2 nC. The figure below shows a small, hollow, plastic sphere hanging vertically from a thin, lightweight thread. The sphere has a mass of 7.10 g and a uniformly distributed charge of 91 Directly below it is a second sphere with the same mass, but a charge of 92 = -58.0 nC. (Assume this second sphere is fixed in place.) The centers of the two plastic spheres are a distance d = 2.00 cm apart. 91 92 (a) What is the tension (in N) in the thread? 0.11154376 N (b) The thread will break if the tension in it exceeds 0.180 N. What is the smallest possible value of d (in cm) before the thread breaks? The analysis is the same as in part (a), including the magnitude and direction of the gravitational and electric forces. Note that Coulomb's law depends on the square of the distance d. Use the threshold value of the tension to solve for d. cm

I 145⁰ I L I I 2m, q E 5) A point charge with known mass 2m and unknown positive charge q is suspended on a massless string in a uniform horizontal electric field of known magnitude E. The string makes a stationary angle = 45° with the vertical. What is a correct expression for the charge q? (HINT: draw a free-body diagram.)

1. Figure below shows an arrangement of four charged particles with 0 = 30.0°and the distance d= 2.00 cm. Particle 2 has charge q2 =+ 8.00x10 -19C; particle 3 and 4 have charges q3=q4=- 1.60 x 10 -19 C. y (a) What is distance D between the origin and particle 2 if the net electrostatic force on particle 1 due to the other particles is zero? (b) If particles 3 and 4 were moved closer to the x axis but maintained their symmetry about that axis, would the required value of D be greater than, less than, or same as part (a)? d D 2 1 4

Two positive point charges, each 15 μC, lie along the x-axis at x = –0.15 m and x = +0.15 m. Find the electric field at (a) the origin (0,0) and (b) the point (0, 0.20 m) on the y-axis. Include a diagram.

A small plastic ball of mass m = 3.00 g is suspended by a string of length L = 17.0 cm in a uniform electric field, as shown in the figure below. If the ball is in equilibrium when the string makes a e = 13.5° angle with the vertical as indicated, what is the net charge on the ball? E = 1.00 × 10³ N/C L