18.2 lesson Electrostatic Forces

Electrostatic Force

  • Description: Stronger than gravitational forces.

  • Nature: Non-contact forces; can be attractive or repulsive.

Forces on Charged Objects

  • Electrostatic forces are affected by the type of charge (positive or negative).

  • Unlike charges attract; like charges repel.

  • The closer the charged objects, the stronger the force.

Demonstrating Forces

  • Bringing a negatively charged rod near a suspended negatively charged object repels it.

  • A negatively charged rod attracts a positively charged rod.

Electroscopes

  • A neutral electroscope has leaves that hang loosely.

  • It can determine the type and amount of charge.

  • Charging occurs by conduction; electrons transfer through direct contact.

Charging by Conduction

  • When a negatively charged rod touches the electroscope:

    • Electrons transfer to the knob, and the leaves spread apart due to repulsion.

  • When a positively charged rod touches the electroscope:

    • Electrons transfer from the electroscope, leaving it positively charged.

Charging by Induction

  • Induction causes electrons in a neutral object to redistribute in response to a nearby charged object.

  • Example: A positive rod causes negative charges to accumulate near it in the neutral object.

Charge Flow and Grounding

  • Grounding allows excess charge to be removed by connecting to Earth, balancing the electroscope's charge.

  • Bringing a charged object near a neutral object induces charge separation.

Coulomb’s Law

  • Two objects exert a force on each other; strength depends on charge and distance.

  • The formula: Force is proportional to the product of the charges and inversely proportional to the square of the distance between them.

Practice Problems

  1. Find the force between two charges separated by 0.30 m.

  2. Analyze force changes when distance between charges is tripled.

  3. Determine net forces acting on charged spheres in various scenarios.