(455) Charging by friction, contact, induction [IB Physics SL/HL]

Charge Transfer Mechanisms

• Charge must be conserved; total charge before equals total charge after.

1. Charging by Friction

• Process Overview:

  • Rubbing two different materials together transfers electrons.

  • Example: Rubbing a balloon on a shirt results in attraction due to charge separation.

  • The balloon gains electrons and becomes negatively charged, while the shirt loses electrons and becomes positively charged.

• Key Points:

  • Opposite charges attract each other (negatively charged balloon attracted to positively charged shirt).

  • Different materials interact differently based on their ability to transfer electrons.

2. Charging by Contact

• Process Overview:

  • When two conductive objects touch, electrons can move between them.

  • Example: If a negatively charged object touches a neutral object, electrons transfer, making both objects negatively charged.

• Key Points:

  • Both materials end up with the same charge (both become negatively charged in the example).

  • Conductors allow easier electron flow compared to insulators, influencing the charge transfer outcome.

3. Grounding (Earthing)

• Process Overview:

  • Connecting an object to the ground provides a pathway for excess electrons to flow away.

  • Example: Using an electrostatic discharge (ESD) bracelet in a lab environment connects to the ground, preventing static build-up.

• Key Points:

  • Grounding effectively neutralizes a positively charged object by allowing electrons to move from the ground to the object, reducing its charge.

  • Common in environments sensitive to static electricity to protect equipment.

4. Charging by Induction

• Process Overview:

  • Necessary components: a charged object (e.g., negatively charged rod) and an uncharged object (e.g., sphere) that do not touch.

  • The charged object repels like charges in the neutral object, causing a redistribution of charges without direct contact.

• Key Points:

  • If the uncharged object is grounded while near the charged object, electrons can flow away, resulting in a charged object (positively charged after grounding) and a negatively charged rod.

  • Similar to charging by friction, induction can also lead to opposite charges.

Summary

• Three Mechanisms of Charge Transfer: Friction, Contact, Induction, with grounding as a method to control charge levels.

• The interactions depend on the materials involved and whether they are conductive or insulative.