Question

two students are experimenting with two objects – a neutral metal sphere and a negatively-charged aluminum pie plate. they momentarily touch the pie plate to the sphere and pull it away. the metal sphere becomes charged negatively. the pie plate remains negatively-charged, but has less excess negative charge than it previously had. complete the analysis of this situation.

images of before and after states of the sphere and pie plate

for each object (sphere before, pie plate before, sphere after, pie plate after), choose from: #p⁺ = #e⁻, #p⁺ > #e⁻, #p⁺ < #e⁻

how did the metal sphere become charged?
options: electrons were added to it., protons were added to it., electrons were removed from it., protons were removed from it.

Explanation:

• A neutral object has equal number of protons (\(p^+\)) and electrons (\(e^-\)).
• A negatively - charged object has more electrons than protons.
• When the negatively - charged pie plate touches the neutral metal sphere, electrons (since they are mobile in metals) move from the pie plate to the sphere.
• Protons are in the nucleus and are not mobile in this context (unlike in some nuclear reactions which are not relevant here).
• Adding electrons to a neutral object (where initially \(\#p^+=\#e^-\)) will make it negatively charged (\(\#p^+<\#e^-\)).

Answer:

Electrons were added to it.