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13 Dec 2019

How does an electroscope work? I have a homework problem that is asking me to sketch an arrangement of excess positive or negative charges in various regions on a picture of an electroscope (that is positiv charged) to show what happens to the charges on the electroscope as a charge rod is brought closer and the deflection of the needle charges.

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Jean Keeling
Jean KeelingLv2
17 Dec 2019
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Related textbook solutions

Physics: Principles with Applications
7th Edition, 2013
Giancoli
ISBN: 9780321625922

Related questions

This is just a conceptual question.

I have an electroscope with a needle inside and a plate on top.When holding a positively charged rod close to it the needle moves,and I understand that this is due to the movement of electrons fromthe neutrally charged needle and up to the plate, leaving theneedle on the bottom more positively charged.

But, what happens when you actually touch the rod to the plate, iknow there must be some sort of exchange or electrons but how doesthis work? does it simply balance the charge between the twoconnecting objects?

Also, how can the net charge be defined in this case. If you don'tactually touch the Rod to the plate is the net charge zero due tono exchange? Basically what is the net charge and how is it definedwhen the rod is touching and when it isnt touching, and when ittouches and is removed. thanks a bunch!

This problem explores the behavior of charge on groundedconductors. We take as an example a long conducting rod suspendedby conducting wires that are connected to ground. Assume that therod is initially electrically neutral. For convenience, we willrefer to the left end of the rod as end A, and the right end of therod as end B . In the answer options for this problem, "stronglyattracted/repelled" means "attracted/repelled with a force ofmagnitude similar to that which would exist between two chargedballs."

A small metal ball is given a negative charge, then brought near(i.e., within about 1/10 the length of the rod) to end A of therod. What happens to end A of the rod when the ball approaches itclosely this first time?

strongly repelled
strongly attracted
weakly attracted
weakly repelled
neither attracted nor repelled

Now consider what happens when the small metal ball is repeatedlygiven a negative charge and then brought into contact with end A ofthe rod.

After a great many contacts with the charged ball, how is anycharge on the rod arranged (when the charged ball is faraway)?

positive charge on end B and negative charge on end A
negative charge spread evenly on both
negative charge on end A with end B remaining neutral
both ends neutral
positive charge spread evenly on both

How does end A of the rod react when the (re)charged ballapproaches it after a great many previous contacts with endA?

strongly repelled
strongly attracted
weakly attracted
weakly repelled
neither attracted nor repelled

How does end B of the rod react when the charged ball approaches itafter a great many previous contacts with end A?

strongly repelled
strongly attracted
weakly attracted
weakly repelled
neither attracted nor repelled



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.

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