A. Electrostatics

Part II – 50 points

15.4 Electric Field

35, 36, 37, 40, 41, 44, 46, 48, 49, 52, 53, 54, 56

37: Remember the field always goes away from the + charge

44: E = kq/r² (since q_o cancels)

52: due to symmetry, the forces on the point by q₁ and q₂ cancel. Therefore, only the force by q₃ has any effect on the point.

54: a) a = F/m = qE/m solve for a.

Next, recall from mechanics that distance x = v_ot + 1/2at² and that v_o = 0m/s since it begins from rest. So, all you have to do is put in a value for a and for t and solve for x.

b) v = v_o + at and again, vo = 0 m/s

c) E = 4pkQ/A solve for Q

56: a) E = 4pkQ/A b) F = qE

15.5 Conductors

59, 60, 62, 63, 64, 65, 66, 67

Answers to Even Problems

36: b

40: no. If you don’t understand why, ask in class – I’ll make something up J.

44: 2.9 x 10⁹ N/C

46: 9.0 x 10⁵ N/C toward the –5.0mC charge.

48: a) (0.080 m, 0) b) yes

52: 1.2 x 10⁶ N/C toward the charge of –4.0mC

54: a) 0.15 m b) 0.60 m/s c) +/- 0.27pC

56: a) 1.1 x 10⁴ N/C b) 1.8 x 10^-15 N

60: yes

62: a

64: a) none b) outward c) none d) outward

66: There are more lines of force at the corners than along the flat lines. Of course the lines of force go IN to negative areas and OUT of positive areas.