A negatively charged rod is brought near a neutral sphere supported
by an insulating stand. What type of charge would you expect to find
on the side of the sphere nearest the rod and on the other side if the
sphere is (a) a conductor and (b) an insulator? Explain.
To determine the type of charge on the sphere and its distribution, we can apply the principles of electrostatics.
(a) If the sphere is a conductor:
- As the negatively charged rod is brought near the neutral conductor (sphere), the negative charges on the rod repel the electrons in the conductor, causing the electrons to move away from the rod.
- The repulsion of electrons leads to an uneven distribution of charges on the conductor. The side of the sphere nearest to the rod will have more positive charge (due to the loss of electrons), while the side farthest from the rod will have more negative charge (as the electrons are repelled to that side).
- Therefore, on the side of the sphere nearest the rod, we would expect a positive charge, and on the other side, a negative charge.
(b) If the sphere is an insulator:
- Insulators do not allow the movement of charged particles freely. Thus, when the negatively charged rod is brought near the neutral insulating sphere, the charges in the sphere are not free to move.
- Due to the electrostatic induction phenomenon, the negative charges in the sphere are repelled by the negative charge on the rod, causing the electrons in the insulator to move further away from the rod.
- This induces a separation of charges across the sphere, with the side nearest to the rod having a slightly positive charge and the other side having a slightly negative charge.
- Therefore, even though the charges in an insulator are not free to move, we would still expect a positive charge on the side of the sphere nearest the rod and a negative charge on the other side due to the effect of induced charges.
In both cases, whether the sphere is a conductor or an insulator, the charge distribution occurs as a result of electrostatic repulsion or electrostatic induction respectively.