Charging by Induction

Two neutral insulated metal spheres

1. Place the two spheres onto insulating stands and touching each other
2. Bring a negatively charged polythene strip near to one sphere
   • Electrons on the sphere closer to the strip is repelled away and moves into the other sphere, leaving behind excess positive charges close to the strip
3. Seperate the two spheres while keeping the polythene strip in position
4. Remove the polythene strip
   • Sphere closer to the polythene strip becomes positively-charged
   • The other sphere becomes negatively-charged
   • The charges are redistrubuted throughout the two spheres evenly since they are conductors

A single insulated metal sphere

1. Bring a positively-charged acetate strip near to a neutral, insulated conductor
   • Electrons are attracted to the positively charged strip on the side closer to the strip. leaving behind positively charges at the other side of the sphere
2. Earth the conductor by touching it with a finger
   • Electrons from the Earth flows up to neutralize the positive charges further away from the strip
3. Finger is then removed from the conductor
4. Acetate strip is removed and the sphere will be negatively-charged

Questions

1. What is the advantage of charging by induction?

The net charge of the original charged object remains unchanged no matter how many times we charge by induction

2. Can we charge a conductor by rubbing?

No. If we are connecting to the ground, excess charges on the conductor in our hands would be able to flow and the conductor becomes neutralized.

3. Can we charge a insulator by induction?

Not really. As only the surface electrons could move by a small distance, an insulator would remain overall neutral as its negative charges cannot leave its surface.