Question

A positively charged ball is brought close to an electrically neutral isolated conductor. The conductor is then grounded while the ball is kept close. Is the conductor charged positively, charged negatively, or neutral if (a) the ball is first taken away and then the ground connection is removed and (b) the ground connection is first removed and then the ball is taken away?

Short answer

a) The conductor is neutral that is not charged if the ball is first taken away and then the ground connection is removed.

b) The conductor is charged if the ground connection is removed first and then the ball is taken away.

Step-by-step solution

Step 1: Stating the given data 

A positively charged ball is brought close to a neutral isolated conductor, and then the conductor is grounded while the ball is kept close.

Understanding the concept of charge by induction

If a charged body is made to come close to an uncharged body, then the uncharged body will acquire charges opposite to the polarity of the charged one due to induction. In a grounded connection, the charges on a body constantly flow from the charged one to the ground to obtain the desired neutral charge condition of the body.

a) Calculation of the polarity of the conductor if ball is taken away then ground connection is removed 

Initially, a neutral conductor is brought close to the positively charged conductor; thus, by induction, the charges will induce at the neutral conductor. Since, a positively charged body is brought near, the induced charge on the neutral conductor will be negative.

Now, if the ball is first taken away and then the ground connection is removed, then the conductor becomes neutral as there will be no charge left when the ball is taken away.

Hence, it will be neutral.

b) Calculation of the polarity of the conductor

From the above part discussion, we get that the neutral conductor is now negatively charged due to the induction charging process.

Now, if the ground connection is first removed and then the ball is taken away, the conductor becomes negatively charged as all the positive charges will be neutralized by grounding.