PHYSICS 3B Study Guide - Midterm Guide: Electric Field, Net Force, Dielectric

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23 Nov 2015

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Find the electric force on the point charge q and express it as a vector. (4 pts) Assume q = 1. 50 c, q = 2. 25 c, d = 3. 00 cm, and d= 4. 00 cm. Since q is negative, the +q charge will attract it, and the q charge will repel it. From the symmetry of the problem, the x components of the two forces will cancel out, leaving only a net force in the +y direction. Fy = (kq|q|/r2)sin + (kq|q|/r2) sin = (2kq|q|/r2) sin where r2 = d2 + d2 and sin = d/(d2 + d2)1/2 . F = (14. 6 n) j: a non-conducting sphere of radius 2a = 50. 0 cm has a uniform charge density = 75. 0 c/m3. A smaller sphere of radius a = 25. 0 cm is removed from it, leaving an empty cavity, as shown. Gauss"s law and the superposition principle to find the electric field at a point (x,y) inside the cavity.

Related Questions

1.Two uncharged, conducting spheres, A and B, are held at rest oninsulating stands and are in contact. A positively charged rod isbrought near sphere A. While the rod is in place, the two spheresare separated. How will the spheres be charged, if at all, afterthey are separated?
Sphere A Sphere B
(a) positive positive
(b) positive negative
(c) negative positive
(d) negative negative
(e) zero zero

2. A charged conductor is brought near an uncharged insulator.Which one of the following statements is true?
(a) Both objects will repel each other.
(b) Both objects will attract each other.
(c) Neither object exerts an electrical force on the other.
(d) The objects will repel each other only if the conductor has anegative charge.
(e) The objects will attract each other only if the conductor has apositive charge.

3. An electron is moved from point A, where the electric potentialis VA = â240 V, to point B, where the electric potential is VB =â360 V. What is the change in the electric
potential energy?
(a) 1.92Ã10â17 J (b) 2.04Ã10â17 J (c) 5.75Ã10â17 J (d) 8.98Ã10â17 J(e) 1.05Ã10â16 J

4. A -2q charge is located a distance d to the right of a +4qcharge, along the x
axis. At which point (or points) along the axis does the electricfield go to zero? To
solve this problem, consider an observer at point P, which is anarbitrary distance x from the +4q charge. Find the value (orvalues) for x (in terms of the separation distance d) where thetotal electric field vanishes.
(a) The electric field is never zero in the vicinity of thesecharges.
(b) The electric field is zero at x = -0.328d.
(c) The electric field is zero at x = +4.22d.
(d) The electric field is zero at both x = -2.26d and x =+2.26d.
(e) The electric field is zero at x = +3.41d.

5. point A is a distance L away from a point charge Q. Point B is adistance 4L away from Q. What is the ratio of the electrostaticpotential at B to that at A, i.e., what is VB/VA?
(a) 1/16
(b) 1/9
(c) 1/4
(d) 1/3
(e) can not be determined without specifying Q and L

6. Which one of the following statements best explains why it ispossible to define an electric potential
in a region of space that contains an electric field?
(a) Work must be done to bring two positive charges closertogether.
(b) Like charges repel one another and unlike charges attract oneanother.
(c) A positive charge will gain kinetic energy as it approaches anegative charge.
(d) The work required to bring two charges together is independentof the path taken.
(e) A negative charge will gain kinetic energy as it moves awayfrom another negative charge.

a)The figure below shows a test charge q betweenthetwo positive charges. Find the force (in newtons) on thetestcharge for q = 2 ÂµC. Give a positive answer iftheforce is to the right and a negative answer if the force is totheleft.

b) For the previous question, find the electric field(innewtons/coulomb) at the position of test charge. Again, supplyapositive value if the electric field points to the right andanegative value if it points to the left.

c) How much work (in joules) is done in moving a charge of 2.5Î¼Cadistance of 53 cm along an equipotential at 10~V?

d) The field lines associated with a uniform electric fieldina region of space are shown in the figure below. Imaginedrawingtwo equipotentials in the plane of the figure, one passingthroughpoint A and and one passing through point B. If the electricfieldis 450 N/C, how much does the potential change in going from AtoB? Provide your answer in volts and use a positive value ifitincreases and a negative value if it decreases.

Please help and you will get a lifesaver rating!! Thankssomuch

a) The electric field at a distance of 2 mm from the center of acharged conducting sphere of

radius 1 mm is 480 N/C. What is the electric field at a distance of6 mm from the center of the sphere?

Find the electric flux through the spherical Gaussian surfaces ofradius 2 mm and 6 mm

whose centers coincide with that of the charged sphere.

(b) At a distance of 2 mm from the axis of a very long conductingcylinder with radius 1 mm,

the electric field is 480 N/C. What is the electric field 6 mm fromthe axis of the

cylinder?

(c) What is the electric field 0.5 mm from the axis of thecylinder?

(d) Assume that the cylinder is now shrunk along its radius so thatit becomes a straight line

that coincides with its axis, and carries the same total charge.What will be the electric

field 0.5 mm from this charged line? Is it different from theresult in the last step? Justify

your answer.

(e) At a distance of 2 mm from a very large uniform sheet ofcharge, the electric field is 480N/C. What is the electric field1.2 cm from the sheet? What is the charge density on the sheet?What is the force on a proton when it is 1.2 cm from the sheet? Aproton carries a charge of -e.

PHYSICS 3B Study Guide - Midterm Guide: Electric Field, Net Force, Dielectric

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