Class 12th Physics Chapter 12 Electrostatics

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Class 12th Physics Chapter 12: Electrostatics

Introduction to Electrostatics
Electrostatics is the branch of physics that deals with the study of electric charges at rest. It encompasses the phenomena and laws governing the forces and fields created by these charges.

Key Concepts and Definitions

  1. Electric Charge:
  • Fundamental property of matter.
  • Two types: Positive (+) and Negative (-).
  • Like charges repel; unlike charges attract.
  1. Coulomb’s Law:
  • Defines the force between two point charges.
  • Formula: ( F = k \frac{q_1 q_2}{r^2} )
  • ( k ) is Coulomb’s constant, ( q_1 ) and ( q_2 ) are the magnitudes of the charges, and ( r ) is the distance between them.
  1. Electric Field:
  • A region around a charged object where other charges experience a force.
  • Defined by: ( E = \frac{F}{q} )
  • Units: Newton per Coulomb (N/C) or Volts per meter (V/m).
  1. Electric Field Lines:
  • Imaginary lines representing the direction of the electric field.
  • Properties: Emanate from positive charges and terminate at negative charges, never cross each other, and the density of lines indicates the field strength.
  1. Electric Flux:
  • Measure of the number of electric field lines passing through a surface.
  • Given by: ( \Phi_E = E \cdot A \cdot \cos(\theta) )
  • Gauss’s Law relates electric flux through a closed surface to the charge enclosed by the surface: ( \Phi_E = \frac{Q_{enclosed}}{\epsilon_0} ).
  1. Electrostatic Potential and Potential Energy:
  • Electric potential (V) at a point is the work done in bringing a unit positive charge from infinity to that point.
  • Electric potential energy (U) of a system of charges is the work done in assembling the system of charges.
  1. Capacitance and Capacitors:
  • Capacitance (C) is the ability of a system to store charge per unit voltage.
  • Given by: ( C = \frac{Q}{V} )
  • Unit: Farad (F).
  • Types of capacitors: Parallel plate, cylindrical, and spherical.
  1. Energy Stored in a Capacitor:
  • Energy (U) stored in a capacitor: ( U = \frac{1}{2} C V^2 )

Important Formulas

  • Coulomb’s Law: ( F = k \frac{q_1 q_2}{r^2} )
  • Electric Field: ( E = \frac{F}{q} )
  • Electric Potential: ( V = \frac{U}{q} )
  • Capacitance: ( C = \frac{Q}{V} )
  • Energy in Capacitor: ( U = \frac{1}{2} C V^2 )

Applications of Electrostatics

  • Capacitors in electronic circuits.
  • Electrostatic precipitators for pollution control.
  • Photocopiers and laser printers.

Practice Problems

  1. Calculate the force between two charges of (2 \mu C) and (3 \mu C) placed 10 cm apart in vacuum.
  2. Determine the electric field at a point 5 cm away from a charge of (1 \mu C).
  3. A capacitor with a capacitance of (10 \mu F) is connected to a 12V battery. Calculate the charge stored and the energy stored in the capacitor.

Conclusion
Electrostatics plays a crucial role in understanding the behavior of electric charges and fields. The principles and equations derived from electrostatics are fundamental to many applications in physics and engineering.

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