Question

A balloon is initially electrostatically neutral. It is then rubbed on against a sweater. The balloon now has a large net negative charge.
How did the balloon obtain a large net negative charge affect the mass and volume?

• A. The mass would increase slightly while the volume would stay the same.
• B. The volume would increase slightly while the mass would stay the same.
• C. Both the mass and volume would increase slightly.
• D. Neither the mass or the volume would increase slightly.

Answer 1

Answer: (C)

Both the mass and volume would increase slightly.

in order gain a negative charge. the balloon would have to gain electrons. the protons are not going to move. Even though the mass of a single electron is small $(9.11\times {10}^{-}31kg)$, a balloon could pick up millions of them, and this would lead to a slight increase in mass.

the electrons also repel each other according to coulomb's law, this would increase the force expanding the balloon leading to a slight increase in volume. Both of these changes would be quite small and you would need special equipment to measure it.