المسائل التالية تغطى الفصل الأول من المقرر (قانون
كولوم)
المسائل باللون الأحمر لطلبة كلية العلوم

(1) Two protons in a
molecule are separated by a distance of 3.8´10^{10}m.
Find the electrostatic force exerted by one proton on the other.
(2) A 6.7mC
charge is located 5m from a 8.4mC
charge. Find the electrostatic force exerted by one on the other.
(3) Two fixed charges, +1.0´10^{6}C
and 3.0´10^{6}C, are 10cm
apart. (a) Where may a third charge be located so that no force acts on it?
(b) Is the equilibrium of this third charge stable or unstable?
(4) Each of two small spheres is charged
positively, the combined charge being 5.0´10^{5}C.
If each sphere is repelled from the other by a force of 1.0N when the
spheres are 2.0m apart, how is the total charge distributed between the
spheres?
(5) A certain charge Q is to be divided
into two parts, q and Qq. What is the relationship of
Q to q if the two parts, placed a given distance apart, are to
have a maximum Coulomb repulsion?
(6) A 1.3mC
charge is located on the xaxis at x=0.5m, 3.2mC
charge is located on the xaxis at x=1.5m, and 2.5mC
charge is located at the origin. Find the net force on the 2.5mC
charge.
(7) A point charge q_{1}=
4.3mC is
located on the yaxis at y=0.18m, a charge q_{2}=1.6mC
is located at the origin, and a charge q_{3}=3.7mC
is located on the xaxis at x= 0.18m. Find the resultant force on
the charge q_{1}.
(8) Three point charges of 2mC,
7mC, and –4mC
are located at the corners of an equilateral triangle as shown in the figure
2.9. Calculate the net electric force on 7mC
charge.
Figure 2.9
(9) Two free point charges +q and +4q
are a distance 1cm apart. A third charge is so placed that the entire
system is in equilibrium. Find the location, magnitude and sign of the
third charge. Is the equilibrium stable?
(10) Four point charges are situated at the
corners of a square of sides a as shown in the figure 2.10. Find the
resultant force on the positive charge +q.
Figure 2.10
(11) Three point charges lie along the yaxis.
A charge q_{1}=9mC
is at y=6.0m, and a charge q_{2}=8mC
is at y=4.0m. Where must a third positive charge, q_{3}, be
placed such that the resultant force on it is zero?
(12) A charge q_{1}
of +3.4mC
is located at x=+2m, y=+2m and a second charge q_{2}=+2.7mC
is located at x=4m, y=4m. Where must a third charge (q_{3}>0)
be placed such that the resultant force on q_{3} will be
zero?
(13) Two similar conducting balls of mass m
are hung from silk threads of length l and carry similar charges q
as shown in the figure 2.11. Assume that
q is so small that tanq can
be replaced by sinq. Show that
where
x is the separation between the balls (b) If l=120cm, m=10g
and x=5cm, what is q?
