A student sets up the apparatus shown below in a physics laboratory. A neutral metal cylinder is supported by an insulating stand. The student brings a negatively charged plastic strip close to, but not touching, the left-hand end of the cylinder.
While holding the strip in place, the student briefly connects the opposite end of the metal cylinder to the ground using a grounding wire.
Explain why the metal cylinder is left with an overall positive charge after the ground connection is broken and the plastic strip is removed.