**Useful relationships can be
found at ****EQUATIONS.**

**Force problems**

**1. Two charges,
q1 = +50 uC and q2 = +70 uC, are separated by a distance of 60
cm. Determine the force of repulsion for these charges.**

**2. Two identical
copper spheres are .5 m apart. What should be the (equal) charge
on each if the force of repulsion between them is 1 N? How many
electrons must be removed from each to accomplish this? If each
sphere has a mass of 1 gram, what fraction of the atoms present
will lose an electron? What conclusion can you draw from this
calculation.**

**3. Two identical
spheres hold the same amount of negative charge. The spheres are
fixed a permanent distance apart of 1 m, causing a force of repulsion
to be 12 N. A third sphere, identical to the other two but initially
uncharged, is brought close at hand. The third sphere touches
the first sphere, then the second, and is then removed. Determine
the force of repulsion between spheres 1 and 2 now.(Hint: This
is an example of charging by conduction. When sphere 3 touches
sphere 1, the charges redistribute themselves over the surface
of the two spheres in proportion to the area of each.)**

**4. Three charged
bodies lie in a straight line. Body 2 is 1 m to the right of body
1 and both are fixed in place; they cannot move. Body 3 is 1 m
to the right of body 2. It is free to move but does not. How are
charges 1 & 2 related?**

**5. Two pith
balls ( mass = 1 g each) are suspended from strings 1 m long that
are attached to a common point of support. How much (equal) charge
is there on each if the force of repulsion causes the strings
to be separated by 20 degrees?**

**Electric Fields**

**6. Consider
two point charges q1 = +5 x 10^-6 C, q2 = -8 x 10^-6 C, separated
by a distance of 1 m. a) Find E1 at any point 70 cm from q1. Find
E2 at any point 30 cm from q2. What is Enet if these two points
are coincident.**

**7. For the
two charges in problem #11, find the place where Enet = 0. What
is the significance of a place where Enet = 0?**

**8. Three identical
charges, q = +50uC, are located at the corners of a square 25
cm on the side. Determine the magnitude and direction of the E
field at the vacant corner. What is the magnitude and direction
of the electric force exerted on a charge of -40 uC now placed
at the fourth corner?**

**9. Revisit
problem 4. Given your answer for charges 1 & 2, what is Enet
at the site of charge 3?**

**Last edited 12/24/05**