A rod made from insulating material carries a net charge, while acopper sphere i

Question

A rod made from insulating material carries a net charge, while acopper sphere is neutral. The rod and the sphere do not touch. Isit possible for the rod and the sphere to

(a) attract one another?
(b) repel one another? Select all that apply.

If thecopper sphere is grounded before the charged rod is brought close,the rod brought close, and then the ground connection removed; therod and the copper sphere will attract each other. The effect ofthe grounding is to allow charge opposite to the charge on the rodto move onto the copper sphere.

In orderfor the charged rod and uncharged copper sphere to repel there mustbe charge on the copper sphere, on the side of the copper sphereclose to the approaching rod, that has the same sign as the chargeon the rod. Without deliberately adding this like charge to thecopper sphere it is not possible to get the rod and the sphere torepel. It ispossible for the rod and sphere to attract. They will attractnaturally if the two are brought close to each other withouttouching. As the rod nears the uncharged copper sphere mobileelectrons on the copper will either move to or away from the sideof the sphere the chraged rod is close to depending on whether therod is positively or negatively charged, respectively. Theresulting unbalanced and unequal charge condition leads toattraction between the rod and the copper sphere. Thecharged rod and the uncharged copper sphere will always repel eachother when the two are brought close to each other withouttouching. Thecharged rod and the uncharged sphere can repel each other if thecharge on the rod, when the rod attracted the neutral coppersphere, is removed and replaced with the opposite charge. Then therod and copper sphere will repel. If thecopper sphere is grounded before the charged rod is brought close,the rod brought close, and then the ground connection removed; therod and the copper sphere will attract each other. The effect ofthe grounding is to allow charge opposite to the charge on the rodto move onto the copper sphere.

In orderfor the charged rod and uncharged copper sphere to repel there mustbe charge on the copper sphere, on the side of the copper sphereclose to the approaching rod, that has the same sign as the chargeon the rod. Without deliberately adding this like charge to thecopper sphere it is not possible to get the rod and the sphere torepel. It ispossible for the rod and sphere to attract. They will attractnaturally if the two are brought close to each other withouttouching. As the rod nears the uncharged copper sphere mobileelectrons on the copper will either move to or away from the sideof the sphere the chraged rod is close to depending on whether therod is positively or negatively charged, respectively. Theresulting unbalanced and unequal charge condition leads toattraction between the rod and the copper sphere. Thecharged rod and the uncharged copper sphere will always repel eachother when the two are brought close to each other withouttouching. Thecharged rod and the uncharged sphere can repel each other if thecharge on the rod, when the rod attracted the neutral coppersphere, is removed and replaced with the opposite charge. Then therod and copper sphere will repel.

Explanation / Answer

When you bring the charged rod close to the sphere it createsa dipole by pushing away(rod negative)/drawing toward you (rodpositive) the electrons in the sphere. This makes one side of thesphere charged, and makes it attracted to the rod.
The only way it will repel is if somehow you can get the samesign charge on the sphere, by charging it or by having some otherstronger charged body induce a dipole on it.
Opposite sign charges repel, same sign chargesattract.

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