Some questions about ELECTRIC CHARGE ADN ELECTRIC FIELD

[willdefender]

1.If you charge a pocket comb by rubbing it with a silk scarf, how can you determine if the comb is positively or negatively charged?

6.Contrast the net charge on a conductor to the "free charges" in the conductor.

7.A charged rod placed near an unchanged metal object can attract(or repel) electrictrons. There are a great many electrons in the metal, yet only some of them move. Why not all of them?

12. What experimental observations mentioned in the text rule out the possibility that the numerator in Coulomb's law contains the sum (Q1 and Q2)rather than the product Q1Q2?

20.Show, using the three rules for field lines, that the electric field lines starting or ending on a single point charge must be symmetrically spaced around the charge.

THREE RULES:
A.The field lines indicate the direction of the electric field;the field points in the direction tangent to the field line at any point;
B.The lines are drawn so that the magnitude of the electric field, E, is proportional to the number of lines crossing unit area perpendicular to the lines. The closer the lines, the stronger the field;
C.Electric field lines start on positive charges and end on negative charges; and the number starting or ending is proportional to the magnitude of the charge.

23.Consider a small positive test charge located on an electric field line at some point, such as point P. Is the direction of the velocity and/or acceleration of the test charge alone this line? Discuss.

24.We wish to determine the electric field at a point near a positively charged metal sphere(a good conductor).We do so by bringing a small test charge, q0, to this point and measure the force F0 on it. Will F0/q0 be greater than, less than, or equal to, the electric field E as it was at that point before the test charge was present?

 

[zhermes]

Everyone on the forums is happy to help, but they won't simply answer homework problems for you. For each of the above problems please describe your attempts at the solution, or particular points that you are confused about so we can help as efficiently as possible.

 

[willdefender]

1.If you charge a pocket comb by rubbing it with a silk scarf, how can you determine if the comb is positively or negatively charged?
----Our teacher suggest to use the electroscope which has some charged on the leaves originally.And then put the comb near the metal of the electroscope but not touch it.He said in this way we can test it. But I didn't understand the process.

6.Contrast the net charge on a conductor to the "free charges" in the conductor.
----I think, as for the net charge on a conductor, we can consider the conductor as a whole, then, net charge is what the whole shows, positive or negative and how many of them.
As for free charges, I think it is the charge that can move in the conductor freely, such as the valence electrons.

7.A charged rod placed near an unchanged metal object can attract(or repel) electrictrons. There are a great many electrons in the metal, yet only some of them move. Why not all of them?
----I think only some of them move because only the valence electros have larger possibility to move. But our teacher said that some of them move because the electrons have reached a dynamic balance before all of them move.

12. What experimental observations mentioned in the text rule out the possibility that the numerator in Coulomb's law contains the sum (Q1 and Q2)rather than the product Q1Q2?
----I don't make out what this question means.

20.Show, using the three rules for field lines, that the electric field lines starting or ending on a single point charge must be symmetrically spaced around the charge.

THREE RULES:
A.The field lines indicate the direction of the electric field;the field points in the direction tangent to the field line at any point;
B.The lines are drawn so that the magnitude of the electric field, E, is proportional to the number of lines crossing unit area perpendicular to the lines. The closer the lines, the stronger the field;
C.Electric field lines start on positive charges and end on negative charges; and the number starting or ending is proportional to the magnitude of the charge.
----I think A tells us about the direction of the lines, we learn the dirction of the field lines produced by a single point is either towards or outwards the point.

23.Consider a small positive test charge located on an electric field line at some point, such as point P. Is the direction of the velocity and/or acceleration of the test charge alone this line? Discuss.
----I think both of them are not on that line but on the diretion of the line.

24.We wish to determine the electric field at a point near a positively charged metal sphere(a good conductor).We do so by bringing a small test charge, q0, to this point and measure the force F0 on it. Will F0/q0 be greater than, less than, or equal to, the electric field E as it was at that point before the test charge was present?
----It depends. If the point charge is positive(the same with the test charge),it will be less.If it is negative, it will be larger.

 

[willdefender]

Everyone on the forums is happy to help, but they won't simply answer homework problems for you. For each of the above problems please describe your attempts at the solution, or particular points that you are confused about so we can help as efficiently as possible.

Thank you for your suggestions! This is my first time discussing questions here. I hope the ones below will satisfy the requires here!

 

[paranormal]

I would like to provide the following responses to the questions about electric charge and electric field:

1. To determine if the comb is positively or negatively charged, you can use a charged object such as a balloon or another comb to see if it is attracted or repelled by the pocket comb. If it is attracted, then the pocket comb is negatively charged, and if it is repelled, then the pocket comb is positively charged.

6. The net charge on a conductor is zero, meaning that the positive and negative charges are balanced. However, there are free charges present in the conductor that can move within the material. These free charges are not necessarily equal to the net charge on the conductor.

7. The charged rod placed near the unchanged metal object can only attract or repel a certain number of electrons because the metal has a high number of free electrons, but they are still bound to the atoms in the metal. Only the outermost electrons can easily move in response to the charged rod, while the inner electrons are more tightly bound and do not move as easily.

12. The experimental observations that rule out the possibility of the numerator in Coulomb's law containing the sum (Q1 and Q2) instead of the product Q1Q2 are the results of the inverse square law. This law states that the force between two charged objects is inversely proportional to the square of the distance between them. If the numerator contained the sum of the charges, the force would not decrease as the distance between the objects increased, which is not observed in experiments.

20. According to the three rules for field lines, the electric field lines starting or ending on a single point charge must be symmetrically spaced around the charge. This is because the field lines indicate the direction of the electric field, and they are drawn so that the magnitude of the electric field is proportional to the number of lines crossing unit area perpendicular to the lines. Therefore, the closer the lines, the stronger the field, and they must be symmetrically spaced to maintain this relationship.

23. The direction of the velocity and/or acceleration of a small positive test charge located on an electric field line at a point such as point P will depend on the direction of the electric field at that point. If the electric field is pointing towards the positive charge, then the test charge will have a positive velocity and/or acceleration along the field line. If the electric field is pointing away from the positive charge, then the test charge