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Home Minds On Static Electricity Mission SE7 Charging by Induction - Electrophorus Plate Help Help 5

Mission SE7 Charging by Induction - Electrophorus Plate

The Question

A positively charged piece of styrofoam is placed on the table. A neutral aluminum plate is brought near as shown below. While held above the styrofoam, the aluminum plate is touched (grounded). At this point, there is a movement of electrons. Electrons move ____ .

Physics Rules

Charging by Induction:
Charging by induction is the 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 the ground and 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.

Think About It

Opposites attract. Likes repel. And only electrons can move. That's the key to understanding charging by induction. When the aluminum plate is brought near the positively charged styrofoam, a movement of electrons is induced within the aluminum plate. Which way do electrons move? Being attracted by the positively charged styrofoam, electrons will tend to move from the rim of the aluminum plate to the bottom in order to get closer to the styrofoam. Charge is now polarized within the aluminum plate, with the top rim having lost electrons and bottom side having gained electrons. When the aluminum plate is touched to the ground, electrons in the ground are attracted to the positively charged styrofoam as well. They enter the aluminum plate from the ground and the aluminum becomes charged. The aluminum plate is said to have been charged by induction using the positively charged styrofoam.

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