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

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