1. CH21-26.Problems Exam 2 Review JH

5. b and c tie, then a (zero)

6. The net force is zero at the origin and zero at the infinity and thus it must have some maximum somewhere in between. The net force is given by: To find the maximum, you must derive this with respect to x then make it equal to zero. ( too long for an exam). The answer is when x = d/Sqrt(2)

21. Using the E field as force is not a good idea The best is to convert the potential energy to kinetic energy: e(V(inf) –V(R)) = -(Kf- Ki ) eV = ½ m v^2  v = Sqrt(2eV/m) = Sqrt(4 e kq/d /m) = 9.4e5 m/s

23. 50.Figure 25-49 shows a parallel-plate capacitor of plate area A= 10.5 cm 2 and plate separation 2d = 7.12 mm. The left half of the gap is filled with material of dielectric constant k 1 = 21.0; the top of the right half is filled with material of dielectric constant k 2 = 42.0; the bottom of the right half is filled with material of dielectric constant k 3 = 58.0.What is the capacitance? Answer: 4.55×10 -11 = 45.5 pF