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1.Two point charges are initially 8.00 cm apart, and are then moved so that they are 2.00cm apart. If the initial force between these point charges were F, what is the new force in terms of the initial force?

2. Two identical conducting spheres have charges - 4.50 x 10-5 C and 5.50 x 10-5C and are in fixed positions, 11.5 cm apart

a) Calculate the electrostatic force acting on the two charges

b) The spheres are touched together and returned to their original positions. Calculate the new electrostatic force acting on them?

3. Consider two pith balls each have a mass of 22.5 g. One pith ball is suspended by an insulating thread. The other is brought near the suspended ball. Both the balls have equal and opposite charges. The suspended ball is now hanging forming an angle 27 0  to the vertical. The distance between the balls is 5.0 cm. The ball is in equilibrium with Fe, mg and T adding vectorially to yield zero. Calculate mg, Fe and charge on each ball.

4. Three charges A, B and C of + 7.5, - 6.5  and + 5.5 respectively are arranged at the corners of a right triangle. Find the magnitude of the force on charge C.

                                                               A

                                                           4.5 cm

                                                            B          5.0C                       C

                                                                         7.0 cm               

5. A single neutral 5.00 g pith ball is touched by a charged rubber rod which had a charge of 4.3 x 10-8 C. The pith ball then comes into contact with another pith ball of equal size and shape. If the two pith balls are hung by two pieces of 5.00 cm thread from a single point and they make an angle of 22.00 between the two, what is the charge remaining on the original charged rod

PHYSICS 30

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6. Three particles with chargesq1 = 2Q , q2 = -2Q, q3 = 4Q are placed at the same distance d from a test charge placed at the origin. Find the electric field at the origin in terms of k, Q and d 

7.  Three charges of +6.00 , 4.5  and 7.5  are placed at the vertices of an equilateral triangle with sides 6.00 cm. Determine the net electric field midway between Q1 and Q2?

                                                                           Q1

                                                             Q2                     Q3

8. Three charges are located at the vertices of an equilateral triangle of side 16 cm. Find the electric field at the center of the triangle?

                                                                                                   6.5microC

                                                     -7.5microC                                 -5.5microC

9. Three charged spheres are depicted below. Assume

     Q1 = 4.25 micro coulomb

     Q2 = 6.55 micro coulomb

     Q3 = - 5.55 micro coulomb

Q1 is located   - 4.00 cm along the y- axis, Q2 is located – 6.0 cm along the x -axis and Q3 is located 8.0 cm along the x- axis.

a)      Find the magnitude and direction of the electric field at the origin

b)      If you now place a - 0.100 micro coulomb charge at the origin what is the magnitude and direction of force on this charge