Please help to clearly explain the solution to this problem on a separate paper.

Question

Please help to clearly explain the solution to this problem on a separate paper. Thank you very much :)

An uncharged piece of cork is hung from a string. When a positively charged rod is brought near but not touching the cork, the rod attracts the cork and the cork hangs as shown. On the diagram at right, sketch how the piece of cork would hang if the north end of a magnet were brought near the cork. Explain. On the diagram at right, sketch how the piece of cork would hang if the south end of a magnet were brought near the cork. Explain.

Explanation / Answer

Well, first you need to know that the fact that a charged object (rod) is attracting a neutral object(cork) is an electrostatic situation. This is what is happening:

** The charged rod is negatively charged.

** The cork is neutral : same amount of electrons orbiting the nucleus as same amount of protons inside the nuclei.

When you put a charged object near a neutral object this charged object will induced (in this case negative charge) charge on the neutral object. By induce I mean that since the rod is negatively charged, when is it brought near the cork, the electrons in the cork atom will be pushed away (from electrostatics: like charges repel) and the protons that reside in the nuclei of the cork atoms will be attracted (again from electrostatics: opposite charges attract). Hence inside the cork you will have one side negative and one side positive (this one being attracted to the negative end of the rod). Now as a whole, the fact that the protons and electrons rearrange inside the cork in a positive side and a negative side is called induced polarization. Why? because this polarization (formation of poles inside a body (positive and negative/ north and south ) was induced by the charged rod.

So in summary what is happening is: "This is an example of electrostatics situation in which induced polarization occurs. The induced polarization is caused due to the induced negative charge of the charged rod on the cork" Keep in mind that induction only occurs when the bodies do not touch. And also that in macroscopic situations charged objects will attract neutral objects.

Hope this answers your questions and helps you understand the concept better. Here is a link that might help too it has nice graphs. http://demoweb.physics.ucla.edu/node/108

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