Download PHYSICS 212–FALL 2016 PROBLEMS IN ELECTROSTATICS Do

PHYSICS 212–FALL 2016
PROBLEMS IN ELECTROSTATICS
Do not use back sides of papers to write on (neither for homework, nor for classwork), since it takes longer
for me to grade the assignment, if I have to turn the pages.
1. A charge of + 2.5 × 10-7 C acts on a charge of + 4.0 x 10-7 C at a distance of 5.0 cm. Find the force acting
on the larger charge. Draw a sketch which shows the vector representing this force.
2. Three charges, A, B, and C, are located on a straight line; B lying between A and C. B is 10 cm from A
and 20 cm from C. Their charges are: A = + 10 x 10 -6 C; B = -20x 10-6 C and C= + 5.0 x 10-6C. Find the
force acting on B due to the charges at A and C. Draw a sketch which shows the charges and show the
directions of the individual forces acting on the charge at B and also the net force acting on B along with its
direction.
3. A right triangle has sides of 30, 40 and 50 cm. A charge of -10 x 10-6 C is placed at the right angle; a
charge of + 10 x 10-6C at the smaller acute angle and a charge of + 5.0x10-6 C at the larger acute angle.
Draw a diagram showing the individual forces and the resultant force acting on the charge at the right
angle. Find the force on the charge at the right angle, and find the angle this force makes with one of the
legs.
4. A hydrogen atom consists of a proton of mass 1.67 × 10 -27 kg and an electron of mass 9.11 × 10-31 kg
which revolves in a circular orbit about the proton. The charge on each is 1.60 × 10 -19C, and they have
opposite signs. Find the speed of the electron if it revolves in an orbit of radius 5.3 x 10 -9cm. (In such an
orbit, the centripetal force is provided by the force of electrostatic attraction between the electron and the
proton.)
5. Find the magnitude of the electric field which will just support a water droplet of mass 10 -6 gm, if the
droplet carries a charge of 10-7 C.
6. A charge of -0.50 µC is situated in an electric field of magnitude 9.0 × 10 4 N/C, directed horizontally to
the right. Find the magnitude and direction of the force on it.
7. Three points, A, B and C, are on the corners of an equilateral triangle. At A there is a point charge of
0.10 µC . A) Find the magnitude and direction of the electric field at a point midway between B and C if
the triangle is 10 cm on a side. B) Repeat the calculation if there is also a charge of 0.10 µC at B. Draw a
sketch in each case showing the magnitude and direction of all fields.
8. Two charges are 36 cm apart. One charge is + 125µC and the other is + 500µC. Find the point along the
line joining them at which the electric field is zero. Draw a diagram, and show each electric field at the
point.
9. Two equally charged spheres, each having mass m, are hanging from a ceiling as shown . The length of
the chord connecting them to the ceiling is L. Find the charge on each of the spheres.
10. At the vertices of a square are located four identical positive point charges. A negative point charge
of 1.15 nC is placed at the center of the square. If the net force on each charge is to be zero, what is the
charge on one of the positive point charges. (Let the length of one of the sides of the square be l.)
DUE: WED. Aug. 31, 2016