PHYA22H3 Chapter 30: PHYA22 Chapter 30.doc

A Van de Graaff generator (see the figure) can develop a very largepotential difference, even millions of volts. Electrons are pulledoff the belt by the high voltage pointed electrode at A, leavingthe belt positively charged. (Recall Example 23-5 where we saw thatnear sharp points the electric field is high and ionization canoccur.) The belt carries the positive charge up inside thespherical shell where electrons from the large conducting sphereare attracted over to the pointed conductor at B, leaving the outersurface of the conducting sphere positively charged. As more chargeis brought up, the sphere reaches extremely high voltage. Considera Van de Graaff generator with a sphere of radius 0.28 m.


(a) What is the electric potential on the surface of the spherewhen electrical breakdown occurs? (Assume V = 0 at r =infinity.)


(b) What is the charge on the sphere for the potential found inpart (a)?

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 = –240 V, to point B, where the electric potential is VB =–360 V. What is the change in the electric
potential energy?
(a) 1.92×10–17 J (b) 2.04×10–17 J (c) 5.75×10–17 J (d) 8.98×10–17 J(e) 1.05×10–16 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.

Hi I need help to solve this problems it would really help me tostudy, hopefully someone can help me with as much details aspossible. (formuas, explanations, etc) thank you in advance!

1. A 50.0 kΩ resistor is connected with a 30.0 μF capacitor and a15.0 V battery with negligible internal resistance. Find the timefor the capacitor to be charged from 0 to 75% of its maximumcharge.

2. A point charge q₁ =5.00nC is placed at x=4.00cm,and a second point charge q_{2=-3.00 nC is placed at x= 6.00cm.}

a)What is the magnitude and direction of the electric field dueto the charges, at the origin x= 0cm?

b) What is the magnitude of the electrical potential at theorigin?

c) What would be the magnitude and the direction of the electricforce on a Q= 8.0nC charged particle subsequently place at theorigin?

d) How much work would be required to place Q ate the origin?Assume that the electric potential at infinity is 0.

Thank you!