A metal plate is connected by a conductor to a ground through a switch. The switch is initially closed. A charge of +Q is brought close to the plate without touching it, and then the switch is opened. After the switch is opened, the charge +Q is removed. What is the charge on the plate then?

Question

A metal plate is connected by a conductor to a ground through a switch.  The switch is initially closed.  A charge of +Q is brought close to the plate without touching it, and then the switch is opened.  After the switch is opened, the charge +Q is removed.  What is the charge on the plate then?

anonymous · Answer

A.) negative, B.)positive, C.) unchanged, D.) Could be either positive or negative, depending on the charge it had before +Q was brought near

jamesj · Answer

This is completely analogous to one of your earlier questions.  And this idea is almost explicitly demonstrated in the lecture I linked to earlier.

anonymous · Answer

right i'm watchign now

anonymous · Answer

i wanna try and figure this one out myself

anonymous · Answer

soon as the baby stops crying :)

radar · Answer

Negative.  The positive charge will attract electrons from earth to the plate.  The switch is then opened thus no return path.  the charge is removed from the vicinity.  The excess electrons are trapped on the plate.  The plate will be negative with respect to both earth and the charge.