Download (Electrostatics) Posted 07/15/2005

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Electrostatics
1.) How many electrons are on a charged comb which attracts a 1 g piece of paper from a distance of 5 cm away,
with an acceleration of 1 cm / s 2 ? Assume that the charge on the comb is equal in magnitude (but of opposite
sign!) to that on the paper. Ignore gravity.
2.)Compare the strengths of the electrostatic and gravitational forces between two isolated electrons.
they be electrically repelled from each other or gravitationally attracted ?
Will
3.) The average lightning stroke has a charge of about 30 C. How many electrons does this represent?
4.) Two small positively charged spheres have a combined charge of 5.12x10 −5 C. If each sphere is repelled
by the other by an electrostatic force of 0.571 N when the spheres are 2.86 m apart, what is the charge on each
sphere?
5.)Calculate the acceleration of an electron released from rest in a uniform electric field of magnitude 20000
N/C.
6.) An electron is accelerated eastward at 1.8 x 109 m/s2 by an electric field. Determine the magnitude and
direction of the electric field. Where is it 1.50 s later?
7.) Calculate electric field, E, at point P(0.5,0.5) if a charge q1 = q is placed at (1,0), q2 = 2q is placed at
(0,0),and q3 = q is placed at (0,1).
8.)What is the acceleration of an electron in a uniform electric field of 1.40x10 6 N/C? (b) How long would it
take for the electron, starting from rest to attain one-tenth the speed of light (c) (c = 3 × 10 8 m/s)? (c) How far
would it travel in that time?
9.)A copper penny has a mass of 3 g. The atomic number of copper is Z=29 and the atomic mass is 63.5
g/mole. What is the total charge of all the electrons in the penny?
10.)What must be the charge on each of two 100 kg spherical masses in order for the electrical force to equal
the gravitational force?
11.)A bead of charge +Q and another of charge +4Q are fixed a distance D apart. Is there a point between
them where the electric field is zero? Is there any other point where the electric field is zero?
12.) Two small charged particles separated by a distance of three meters are found to exert an attractive
force of 8 × 10−3 N on each other. If the total charge on the two particles is 6 micro C, what is the charge on each
particle?
13.) Three point charges are in line one after another , q1 = - 4 nC, q2 = 5 nC, and q3 = 3 nC (1nC = 10 −9 C ).
The distance between q1 and q2 is 0.5 m and that between q2 and q3 is 0.8m. We first find the force on q2 due to
q1 and q3.
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14.)The charges in Fig below are, with q1 = 5C = - q2 , form what is called a dipole. Find the electric field a
distance d = 10m along the x -axis. Here take distance a = 5m
FIG. 1: Dipole field
15.)A m = 2 g ball is suspended by a l = 20 cm long string as in Fig. 1.6 in a constant electric field of E
= 1000 N/C. If the string makes an angle of θ = 15◦ with respect to the vertical, what is the net charge on the ball?
16.) The three charges in Fig below, with q1 = 8 nC, q2 = 2 nC, and q3 = - 4 nC, are separated by distances r2
= 3 cm and r3 = 4 cm. How much work is required to move q1 to infinity?
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17.) A constant electric field E = 2000 V/m exists as in the Fig below. A 10 C charge of mass 20 g, initially at
rest at x = - 1 m, is released. What is its speed at x = 5 m?
18.) A proton and an electron form two corners of an equilateral triangle with sides of length 3x10 −6 m. What is
the magnitude of their net electric field at the third corner?
19) See webpage http://www.wellesley.edu/Physics/phyllisflemingphysics/106 p electric.html.
only relevant problems for practice.
Pick
20.)
See webpage http://www.wellesley.edu/Physics/phyllisflemingphysics/n108 p potential.html.
Do problems 1,2,3,4,5,6,9,11,13.