Question

 

A conducting ball is neutralized and then electrically isolated.  A + 3.0 μ C charge is then placed near the conducting ball without touching it.

After the charge is brought in, the net charge on the conducting ball will be                            [ Select ]                       ["zero", "positive", "negative"]         .  The surface charge density will be                            [ Select ]                       ["zero", "positive", "negative"]         at points on the conducting ball nearest to the + 3.0 μ C charge, and will be                            [ Select ]                       ["zero", "positive", "negative"]         at points on the conducting ball farthest from the + 3.0 μ C charge.  The net electrical force acting on the + 3.0 μ C charge will be                            [ Select ]                       ["zero", "directed towards the ball", "directed away from the ball"]         .

                           [ Select ]                       ["None", "One", "Two", "Three", "All four"]         of the correct answers above will remain true if the conducting ball were replaced by a non-conducting ball of the same radius and distance to the + 3.0 μ C charge.  The surface charge density of the non-conducting ball will be
Choose one:                            [ Select ]                       ["(A)", "(B)", "(C)", "(D)"]      

(A)	zero everywhere.
(B)	not zero, but smaller in magnitude than the surface charge density of the conducting ball.
(C)	equal to the surface charge density of the conducting ball.
(D)	larger in magnitude than the surface charge density of the conducting ball.

Answer 1

Due to electrostatic induction negative charges will be accumulated near the points on the surface which are closer to the +3 uC charge and positive charges will be accumulated in the farther region of the sphere (as the point charge has positive sign it will attract the negative charges and repel the positive charges)

But the net charge of the sphere will always be zero(as no charge have left or entered the sphere so there is no net increase or decrease of charges )

Since negative charges are closer to the positive charge 3 uC the net force will be directed towards the center , (they will attract each other)

So the answer of the first 3 parts

Answer

After the charge is brought in, the net charge on the conducting ball will be ["zero"]         .  The surface charge density["negative"]         at points on the conducting ball nearest to the + 3.0 μ C charge, and will be ["positive"]         at points on the conducting ball farthest from the + 3.0 μ C charge.  The net electrical force acting on the + 3.0 μ C charge will be ["directed towards the ball"]         .

Now if the conducting sphere is replaced then also the same effect will be produced charges will be accumulated (opposite charges near the point charge and like charges away from it) but this time the effect will be lesser.Therefore

.["All four"]         of the correct answers above will remain true if the conducting ball were replaced by a non-conducting ball of the same radius and distance to the + 3.0 μ C charge

The surface charge density of the non-conducting ball will be

(B)	not zero, but smaller in magnitude than the surface charge density of the conducting ball.

This is so because in conducting sphere the charges accumulated due to the actual movement of charges in the sphere but in non conducting sphere the net surface charge density is produced due to phenomena called as "Electrostatic Polaristion"