A positively charged glass rod attracts an object. The object must be:

While it is intuitive to think that opposite charges attract, electrostatic attraction can also occur between a charged object and a neutral one due to a process called electrostatic induction.

1. Attraction of a Negatively Charged Object

This is the most straightforward case. According to the fundamental law of electrostatics, opposite charges attract each other. Since the glass rod is positively charged, it will exert an attractive force on any negatively charged object.

2. Attraction of a Neutral Object (Induction)

When the positively charged glass rod is brought near a neutral object, the electric field from the rod causes the electrons within the neutral object to shift:

• Polarization: Electrons (negative charges) are pulled toward the side of the object closest to the rod.

• Induced Charges: This creates a concentration of negative charge near the rod and leaves a concentration of positive charge on the far side.

• Net Attraction: Because the negative charges are closer to the rod than the positive charges, the attractive force is stronger than the repulsive force, resulting in a net attraction.

Why "A Magnet" is Incorrect

Magnetism and electrostatics are distinct phenomena in this context. A glass rod (an insulator) does not typically interact with a magnet unless the magnet itself is also carrying a static electric charge or is made of a material that can be polarized.

Important Rule: To confirm if an object is actually charged, repulsion is the only sure test. Attraction can happen with both opposite charges and neutral objects, but repulsion only occurs between two objects with the same charge.