A positively charged electroscope has its leaves widely separated
PHYSICS · Single correct · AP · Physics C: Electricity and Magnetism · Conductors and Capacitors · Conductors and Capacitors
Problem
A positively charged electroscope has its leaves widely separated. A neutral metal rod is slowly brought near (but does not touch) the electroscope’s knob. The leaves are observed to move closer together. Which of the following best explains this observation?
(a) Bringing the conductor close increases the electroscope’s capacitance; with the same amount of charge it now has a lower potential difference, so the leaves no longer repel each other strongly.
(b) Positive charges flow from the leaves up to the knob, neutralizing the leaves so they no longer repel each other.
(c) Electrons in the electroscope are attracted toward the knob, reducing the positive charge on the leaves and decreasing their repulsion.
(d) The nearby rod effectively grounds the electroscope through the air, letting its excess positive charge leak away and causing the leaves to collapse.