Using the electroscope to measure the charges by induction and conduction
An electroscope is an instrument for detecting the presence of static electricity. It consists of two thin metal leaves suspended from a metal hook. When the hook is brought near a source of static electricity, some of the electrons in the hook are pushed to the leaves (if the source is negative) or pulled up to the hook from the leaves (if the source is positive).
Either way, the leaves are now charged the same way as each other so they repel each other. The amount they open up is proportional to the charge of the source (if the sources are always held at the same distance from the hook).
Induction charging is a method used to charge an object without actually touching the object to any other charged object. If such a charged rod is brought near to the hook of an electroscope, it will induce the similarly charged electrons to move away from the rod and the leaves. Since both leaves will have the same charge they will repel each other and move apart.
Charging by conduction means that the charging rod actually touches the electroscope’s hook.
Since there is contact, electrons from the knob would flow onto a positive rod or off of a negative rod.
Charging by conduction leaves the electroscope, with a residual charge identical to that of the charging rod. When the electrified rod touches the electroscope, it is possible to observe that the leaves of the instrument move apart one from the other. The negative charge induced by the metallic rod causes a repulsive action that moves them apart. Using the graduated scale we can measure the size of this charge.