Choose all that are correct from the following. a) If a conductor is positively

Question

Choose all that are correct from the following.

a) If a conductor is positively charged by conduction, some positively charged electrons must have transferred to the conductor from another material.

b) Charge polarization is not possible on an insulator because the electrons in an insulator are not mobile.

c) If one end of a metal rod is brought near (but not touching) a negatively charged object and the metal rod is charge-polarized, the charge polarization in the metal is mainly because the positively charged ions within the metal have moved.

d) When an isolated metal rod (with no electrical connection to anywhere) is charge-polarized by induction, the net electrical charge on the whole metal is still neutral.

e) If a piece of positively charged copper is brought in contact with an initially charge neutral brass sphere, some electrons will move out of the brass sphere.

Explanation / Answer

a) False

It is positively charged due to deficiency of electrons. As otherwise in a neutral conductor positive and negative charges are equal in magnitude. It is only the negative charges i.e. electrons are mobile whereas positive charges are fixed in their locations. So the correct statement is, "If a conductor is positively charged by conduction, some negatively charged electrons must have transferred from conductor to another material."

b) False

Charge polarization is possible on an insulator. It is due to displatement of positive and negative charges within the molecule. When placee in some electric field, positive charges experience force in the direction of electric field and neagive charges opposite to the direction of electric field so their centers get separated within the molecule and induced charges of opposite sigen appear on the opposite surfaces. So the correct statement is, "Charge polarization is possible in an insulator although the electrons in insulator are not mobile, but positive and negative charges may get displaced within the molecules of the insulator under the effect of external electric field,"

c) False

It is the elctrons only which are mobile whereas the positive charges are fixed in their locations, so they cannot leave their place.The correct statement is, "Charge polarization in metal is due to moving away of electrons in the metal rod from the end facing the negatively charge object."

d) True

The statement is true because there is only movement of electrons within the metal rod when it is polarized. Total magnitude of negative and positive charges is still equal, so the net charge on whole metal is still neutral.

e) True

The statement is true, because both brass and copper are conductors, whereas the positively charged copper has deficiency of free electrons and so is at higher potential. The brass sphere is charge neutral and hence is at lower potential compared to copper sphere. As electrons move from lower to higher potential, so they will flow from brass to copper sphere until their potentials become equal.

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