Electric Field & Force Sample Problem

Electric Field & Forces Sample Problems 1. What is the resultant force on the center charge below? Ans: 0.028 N, left q1= +4 C q2= -5 C q3= +6 C d1 to 2= 2 m d2 to 3= 4 m 2. What is the resultant force on the -8 C charge below? Ans: 20.04 N, 97.94 q1= +6 C q2 = +10 C q3 = -8 C d1 to 2 = 30 cm d2 to 3 = 20 cm

3. What is the resultant force on the +4 C charge below? Ans: 18.8 N, 264.5 q1= +4 C q2 = +6 C q3 = -10 C d1 to 2 = 10 cm d1 to 3 = 20 cm  = 60

4. Two pith balls, each with a mass of 0.5 g and carrying charge Q, are hung on strings 35 cm long and suspended from one point. They form a 40 angle between them. What is charge Q? Ans: 0.107 C

5. A proton is placed in a uniform electric field. What must be the magnitude and direction of this field if the electrostatic force acting on the proton just balances its weight? The mass of a proton is 1.67 x 10-27 kg Ans: 1.02 x 10-7 N/C, up. 6. Find the resultant electric field strength at point P as shown below. Ans: 7.20 x 106 N/C, 56 q1= +5.6 C q2 = -3.6 C dpoint P to 5.6 C = 10 cm dpoint P to 3.6 C = 6 cm

7. A +16 C and a +4 C , are separated by a distance of 3 m. How far from the +16 C is the electric field zero? Ans: 2 m 8. Find the resultant force on the +10 C charge. Ans: 18.97 N, -71.6 or 288.4

An example
Four charges are arranged in a square with sides of length 2.5 cm. The two charges in the top right and bottom left corners are +3.0 x 10-6 C. The charges in the other two corners are -3.0 x 10-6 C. What is the net force exerted on the charge in the top right corner by the other three charges? To solve any problem like this, the simplest thing to do is to draw a good diagram showing the forces acting on the charge. You should also let your diagram handle your