Question

What will happen to the negatively charged electrons when the rod touches the foam cup?

Answer 1

When a negatively charged rod touches a foam cup, several things can happen depending on the specific circumstances of the contact.

1. **Charge Transfer**: If the foam cup is a conductor (like a metal cup), electrons from the negatively charged rod can flow into the cup. This happens because the negatively charged rod repels any excess electrons on the foam cup, resulting in a redistribution of charge.

2. **Induced Charge**: If the foam cup is an insulator (like a typical foam cup), the negative charge on the rod may induce a separation of charges within the cup. The electrons in the foam cup will be repelled away from the area in contact with the rod, leading to a temporary polarization of the cup. However, because the cup is an insulator, there won't be a significant flow of electrons.

3. **Neutralization**: If the foam cup was initially uncharged, touching the negatively charged rod directly could cause it to acquire an overall negative charge, depending on whether electron transfer occurs. Conversely, if a positively charged object (or ground) is nearby, the excess electrons may be attracted away, neutralizing the negative charge.

In summary, if the foam cup is conductive and the rod touches it, the electrons may transfer from the rod to the cup, resulting in both objects having a negative charge. If the cup is insulating, charge won't transfer, but it may become polarized in the presence of the negatively charged rod.