This only happens when you touch it before lifting it. Let s figure out how the electrophorus works. The cutting board charges up negatively. Think of the soda can. When you touch the rim, the charges from the rim jump on your hand.
Charges are like little balls.
They can be pushed around, transferred from one place to another, selected according to sign or mixed all together. We can give the neutral pie pan a positive charge by removing negative charges by removing the negative charges repelled by the cutting board. You already know a few ways you can test whether an object is charged or neutral. There is, however, a physical device called electroscope built for this. Let s get familiar with it.