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Charging by Induction:
Charging by induction is a charging process that involves charging an object without touching the object to a charged object. The charged object is brought near to the object to be charged (a neutral object). The charged object's presence induces a movement of electrons within the neutral object, causing it to become polarized. Then the neutral object is touched to a ground, causing a transfer of electrons between ground the neutral object. The ground is pulled away, the charged object is pulled away and the neutral object has been charged. When the process is complete, both objects are charged with the opposite type of charge.
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The role of the balloon in this induction charging process is to polarize the two can system by inducing a movement of electrons from one can to the other can. A negatively charged balloon would repel electrons and cause many of them to move from can X to can Y. A positively charged balloon would attract electrons and cause many of them to move from can Y to can X. This movement of electrons leaves one can with a negative charge and the other with a positive charge. The two-can system is then said to be polarized.
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Many students have the misconception that the presence of the charged balloon will attract or repel protons in the pop cans and move the protons closer or farther away. But don't be fooled! Protons are indeed positively charged and attracted to negatively charged objects and repelled by positively charged objects. But protons are present in the nucleus of atoms and as such are tightly bound in that location. The charging of objects always occurs by means of a movement of electrons - either off an object or onto an object. Protons never move.
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