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Electricity and Magnetism

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Isolated Sphere of Unknown Material

EANDM-NIT4XG

As shown in figure (a) below, you touch a neutral (uncharged), isolated sphere of an unknown material with a positively charged rod. Then you remove the rod and bring another positively charged rod, suspended by a string near the left side of the sphere. You observe that the suspended rod is repelled by the sphere figure (b). When you bring the suspended rod near the right side of the sphere, it is not repelled or attracted figure (b).

Which of the following is the best explanation for your observations?

A

The sphere is made of a conductor. When you touch the positively charged rod to the sphere, negative charge is transferred from the sphere to the rod. Since the sphere is a conductor, the net positive charge stays at the point of contact. As such, when you bring the suspended rod to the left side, it is repelled. However, because the charge is isolated to the left side, there is no reaction when you bring it to the right side.

B

The sphere is made of a conductor. When you touch the positively charged rod to the sphere, positive charge is transferred from the rod to the sphere. Since the sphere is a conductor, the net positive charge stays at the point of contact. As such, when you bring the suspended rod to the left side, it is repelled. However, because the charge is isolated to the left side, there is no reaction when you bring it to the right side.

C

The sphere is made of an insulator. When you touch the positively charged rod to the sphere, negative charge is transferred from the sphere to the rod. Since the sphere is an insulator, the net positive charge stays at the point of contact. As such, when you bring the suspended rod to the left side, it is repelled. However, because the charge is isolated to the left side, there is no reaction when you bring it to the right side.

D

The sphere is made of an insulator. When you touch the positively charged rod to the sphere, positive charge is transferred from the rod to the sphere. Since the sphere is an insulator, the net positive charge stays at the point of contact. As such, when you bring the suspended rod to the left side, it is repelled. However, because the charge is isolated to the left side, there is no reaction when you bring it to the right side.