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



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

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

When the negatively charged rod touches the foam cup, the electrons in the foam cup will be repelled by the negative charge on the rod. As a result, the electrons will move away from the side of the foam cup that is in contact with the rod.