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HW_2_solutions

# HW_2_solutions - Physics 21 Solutions for HW 2 due online 1...

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Physics 21, Solutions for HW 2: due online 1 AM, Friday, January 21, 2011 Chapter 22, Problem 4 Two particles are fixed to an x axis: particle 1 of charge -6.76 x 10 -7 C is at the origin and particle 2 of charge +6.76 x 10 -7 C is at x = 21.8 cm. Midway between the particles, what is the magnitude of the net electric field? Solutions:. With x 1 = 6.00 cm and x 2 = 21.00 cm, the point midway between the two charges is located at x = 13.5 cm. The values of the charge are q 1 = q 2 = 2.00 10 7 C, and the magnitudes and directions of the individual fields are given by: 9 2 2 7 5 1 1 2 2 0 1 9 2 2 7 5 2 2 2 2 0 2 | | (8.99 10 N m C )| 2.00 10 C| ˆ ˆ ˆ i i (3.196 10 N C)i 4 ( ) 0.135 m 0.060 m (8.99 10 N m C )(2.00 10 C) ˆ ˆ ˆ i i (3.196 10 N C)i 4 ( ) 0.135 m 0.210 m q E x x q E x x Thus, the net electric field is 5 net 1 2 ˆ (6.39 10 N C)i E E E Chapter 22, Problem 10 Part (a) of Fig. 22-33 shows two charged particles fixed in place on an x axis with separation L . The ratio q 1 / q 2 of their charge magnitudes is 4.05. Part (b) of the figure shows the x component E net,x of their net electric field along the x axis just to the right of particle 2. The x axis scale is set by x s = 30.3 cm. (a) At what value of x > 0 is E net,x maximum? (b) If particle 2 has charge -5 e , what is the value of that maximum? Assume e = 1.602 × 10 -19 C.

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