Question

two students are experimenting with two objects — a neutral aluminum pie plate and a positively - charged metal sphere. they momentarily touch the metal sphere to the pie plate and pull it away. the pie plate becomes charged positively. the metal sphere remains positively - charged, but has less excess positive charge than it previously had. complete the analysis of this situation.
before
#p⁺ = #e⁻
#p⁺ > #e⁻
#p⁺ < #e⁻
#p⁺ = #e⁻
#p⁺ > #e⁻
#p⁺ < #e⁻
after
#p⁺ = #e⁻
#p⁺ > #e⁻
#p⁺ < #e⁻
#p⁺ = #e⁻
#p⁺ > #e⁻
#p⁺ < #e⁻
how did the pie plate become charged?
electrons were added to it.
protons were added to it.
electrons were removed from it.
protons were removed from it.

Explanation:

Before

• The pie plate is neutral, so the number of protons (\(\#p^{+}\)) equals the number of electrons (\(\#e^{-}\)), i.e., \(\#p^{+}=\#e^{-}\).
• The metal sphere is positively - charged, so \(\#p^{+}>\#e^{-}\).

After

• The pie plate is positively - charged, so \(\#p^{+}>\#e^{-}\).
• The metal sphere still has a positive charge (but less than before), so \(\#p^{+}>\#e^{-}\).

Charge mechanism

• Protons are in the nucleus and are not easily transferred in such a simple contact - charging scenario.
• When the positively - charged metal sphere touches the neutral pie plate, electrons (\(e^{-}\)) are attracted to the sphere (because the sphere has a deficiency of electrons). So electrons are removed from the pie plate, making the pie plate positively charged.

Answer:

Before: Pie plate - \(\#p^{+}=\#e^{-}\), Sphere - \(\#p^{+}>\#e^{-}\)
After: Pie plate - \(\#p^{+}>\#e^{-}\), Sphere - \(\#p^{+}>\#e^{-}\)
Charge mechanism: Electrons were removed from it.