A student is investigating the distribution of charges in insulators. The student will place an aluminum metal can on top of a foam cup and touch the side of the foam cup with a negatively charged rod. The set up for the investigation is shown in the diagram.

What will MOST LIKELY happen to the electrons when the rod touches the foam cup?

A.
The electrons will pass to the foam cup but will remain in a localized, positively charged area on the cup where the rod was placed.

B.
The electrons will pass to the foam cup but will remain in a localized, negatively charged area on the cup where the rod was placed.

C.
The electrons will pass from the foam cup to the aluminum can, and both the foam cup and the aluminum can will become positively charged.

D.
The electrons will pass from the foam cup to the aluminum can, and both the foam cup and the aluminum can will become negatively charged.

1 answer

When the negatively charged rod touches the foam cup, it will transfer some of its excess electrons to the foam cup. This will result in the foam cup becoming negatively charged as it gains electrons. Here’s a breakdown of the options:

A. The electrons will pass to the foam cup but will remain in a localized, positively charged area on the cup where the rod was placed.

  • Incorrect. Electrons will not create a positively charged area; the cup gains negative charge instead.

B. The electrons will pass to the foam cup but will remain in a localized, negatively charged area on the cup where the rod was placed.

  • Correct. The foam cup becomes negatively charged in the area where the rod makes contact.

C. The electrons will pass from the foam cup to the aluminum can, and both the foam cup and the aluminum can will become positively charged.

  • Incorrect. This contradicts the behavior of negatively charged objects; electrons would not leave to make both objects positively charged.

D. The electrons will pass from the foam cup to the aluminum can, and both the foam cup and the aluminum can will become negatively charged.

  • Incorrect. The foam cup gains negative charge, but typically the can would remain neutral unless it is part of a closed conductor system receiving electrons.

Thus, the most accurate answer regarding the behavior of electrons in this scenario is:

B. The electrons will pass to the foam cup but will remain in a localized, negatively charged area on the cup where the rod was placed.