A teacher places a metal can on top of an insulating foam cup and touches the side of the cup with a negatively charged rod. The setup is shown in the picture below.

Question

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

The electrons will transfer from the cup to the metal can, causing both the cup and can to have a negative charge.
The electrons will transfer from the cup to the metal can, causing both the cup and can to have a negative charge.

The electrons will transfer from the cup to the metal can, causing both cup and can to have a positive charge.
The electrons will transfer from the cup to the metal can, causing both cup and can to have a positive charge.

The electrons will transfer to the cup and will remain in a concentrated, negatively charged area on the cup where the rod was placed.
The electrons will transfer to the cup and will remain in a concentrated, negatively charged area on the cup where the rod was placed.

The electrons will transfer to the cup and will remain in a concentrated, positively charged area on the cup where the rod was placed.

Answer 1

When the negatively charged rod touches the foam cup, the excess electrons from the rod will transfer to the foam cup. This occurs because the insulating properties of the foam cup prevent the electrons from moving away freely and instead cause them to localize in the material of the cup.

As a result of this transfer, the foam cup will become negatively charged due to the additional electrons, and the metal can—which is conductive and in contact with the foam cup—will also gain some negative charge from the cup. Therefore, both the cup and the can will end up with a negative charge.

So the correct statement is:

The electrons will transfer from the rod to the cup and will remain in a concentrated, negatively charged area on the cup where the rod was placed.