Methods of Charging

Review of previous concepts:
- Types of charges: positive, negative, and neutral.
- Polarization: Redistribution of charge within a neutral object when a charged object is nearby. The object remains neutral overall.

Process: A charged object touches a neutral object.
Charge transfer: Charge moves from the charged object to the neutral object.
Result: The neutral object acquires the same charge as the charged object.
Example:
- A negatively charged rod touches a neutral metal sphere. Electrons transfer to the sphere, making it negatively charged.
- A positively charged object touches a neutral object, the neutral object also becomes positive. (loses electrons)
Protons do not move: Movement of protons would change the mass of the object.
Equilibrium: After contact, both objects have the same amount of charge.
- If one object has a charge of $2$ coulombs after contact, the other also has $2$ coulombs.

Process: Two insulators are rubbed together.
Charge transfer: Electrons transfer from one material to the other.
Result: The objects acquire opposite charges.
- Rubber rod rubbed with fur: The rubber rod becomes negatively Y charged, and the fur becomes positively charged.
- PVC pipe rubbed with fur: Similar to rubber rod, becomes negatively charged.
- Glass rubbed with silk: The glass becomes positively charged, and the silk becomes negatively charged.
Charge conservation: The magnitude of charge is equal but opposite.
- If the rubber rod has a charge of $-2$ coulombs, the fur has a charge of $+2$ coulombs.
- If the glass has a charge of $+3$ coulombs, the silk has a charge of $-3$ coulombs.

Process: Connecting a charged object to the earth (ground) via a conductor.
Charge flow: Charge flows either from the earth to the object or from the object to the earth.
Result: The object becomes neutral.
- Touching a positively charged sphere: Electrons flow from the person (ground) into the sphere to neutralize it.
- Touching a negatively charged sphere: Electrons flow from the sphere into the person and down to the earth.
Real-life example: Lightning rods
- A rod connected to a wire that goes into the ground, directing lightning charge into the earth.

Two-step process:
- Polarization: A charged object is brought near a neutral object, causing charge redistribution within the neutral object.
- Grounding: The polarized object is grounded, allowing charge to flow to or from the ground.
Scenario 1: Negatively charged rod near a neutral sphere:
- Electrons in the sphere move away from the rod (polarization).
- The sphere is grounded on the side opposite the rod.
- Electrons leave the sphere through the ground.
- The sphere becomes positively charged.
Scenario 2: Positively charged rod near a neutral sphere:
- Electrons in the sphere move toward the rod (polarization).
- The sphere is grounded on the side opposite the rod.
- Electrons flow from the ground into the sphere.
- The sphere becomes negatively charged.
Rule of thumb:
- A negatively charged rod induces the opposite charge (positive) in the neutral object.
- A positively charged rod induces the opposite charge (negative) in the neutral object.

Tuna cans taped to plastic bottles (insulated):
- Charging by induction: A positively charged glass tube polarizes the cans. One can becomes negatively charged (gains electrons), and the other becomes positively charged (loses electrons).
- Charging by contact: Touching the cans with a charged object transfers the charge.
Franklin Bell (Benjamin Franklin):
- Van de Graaff generator (positively charged) attracts a neutral soda can.
- The can touches the generator, loses its charge, and becomes neutral.
- A person can act as a ground: When the can hits a grounded person (touching a metal sink), the charge is removed from the can.
Induction and Grounding Demonstration:
- Two objects are charged by induction (negative and positive).
- The objects are grounded, becoming neutral.