Day 106

Charging by Conduction

  • Requires two conductors to come into direct contact with each other
  • The two objects acquire exactly the same charge after conduction occurs

Example #1: if the first object has a zero charge and the second object has a -10 C charge, the two bodies will each have a -5C charge after conduction. [(-10 + 0)/2 = -5C] Since the -10 C body had a surplus of electrons, some moved to the neutral body. (Remember, positive charges do not move!)

Example #2: Object #1 has a +5C charge; Object #2 has a -5C charge. After conduction, both acquire a net charge of zero! The electrons from the -5C object moved over to the +5C object, thereby canceling the charge on both objects!

Example #3: Object #1 has a +4C charge; Object #2 has a +6C charge. The charge of each after conduction is………+5C. Which object had more electrons to begin with? The +4C object had more electrons, so -1C of charge moved from the +4C object to the +6C object. or (4 + 6)/2 = 5.

Charging by Induction

  • Step 1: Bring a negatively-charged rod near a neutral spherical object. The charges on the neutral object redistribute to bring the positive charges near the negative rod. Electrons in the sphere are repelled from the electrons in the rod.
  • Step 2: Add a grounding wire to the sphere and some electrons will leave the sphere and travel to the Earth

When is something “grounded”? When a conductor has been connected to the Earth by means of a conducting wire such as a copper pipe (The Earth is an infinite reservoir of electrons)

  • Step 3: Remove the grounding wire and the sphere has a positive charge remaining.
  • Step 4: Remove the negative rod and the positive charge redistributes itself on the surface of the sphere since the positive charges are repelled from each other and try to get as far away as possible.

In summary, induction requires two conductors that are brought near each other.   The resulting charge is opposite from that object which produced the charge.