Electrostatics: What is Electrostatics: Conductors, Insulators, and Semiconductors (For CBSE, ICSE, IAS, NET, NRA 2022)

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Title: Electrostatics

What is Electrostatics?

  • Electrostatics, as the name implies, is the study of stationary electric charges.
  • Study of stationary electric charges at rest is known as electrostatics. An electroscope is used to detect the charge on a body
  • A rod of plastic rubbed with fur or a rod of glass rubbed with silk will attract small pieces of paper and is said to be electrically charged.
  • Pith ball electroscope is used to detect a charge and to know the nature of the charge.
  • The charge on plastic rubbed with fur is defined as negative, and the charge on glass rubbed with silk is defined as positive.
  • Gold leaf electroscope which was invented by Bennet detects a charge and the nature of the charge and determines the quantity of the charge.
  • Charge is conserved.
  • A neutral object has no net charge.
  • If the plastic rod and fur are initially neutral, when the rod becomes charged by the fur, a negative charge is transferred from the fur to the rod.
  • Net negative charge on the rod is equal to the net positive charge on the fur.

Conductors, Insulators, and Semiconductors

  • A body in which electric charge can easily flow through is called conductor (e. g. metals) .
  • A conductor is a material through which electric charges can easily flow.
  • A body in which electric charge cannot flow is called insulator or dielectric. (E. g. glass, wool, rubber, plastic, etc.) An insulator is a material through which electric charges do not move easily, if at all
  • Substances which are intermediate between conductors and insulators are called semiconductors. (e. g. silicon, germanium, etc)
  • An electroscope is a simple device used to indicate the existence of charge.
  • Dielectric Strength: It is the minimum field intensity that should be applied to break down the insulating property of insulator.

Surface Charge Density (Σ)

  • The charge per unit area of a conductor is defined as surface charge density

  • When then,
  • Its unit is coulomb/meter and its dimensions are .
  • It is used in the formula for the charged disc, charged conductor and an infinite sheet of charge etc.
  • Surface Charge Density depends on the shape of the conductor and presence of other conductors and insulators in the vicinity of the conductor.

Electric Flux

  • The number of electric lines of force crossing a surface normal to the area gives electric flux
  • Electric flux through elementary area ds is defined as the scalar product of area and field.

Electric Potential (V)

  • An electric potential at a point in a field is the amount of work done in bringing a unit + ve charge from infinity to the point.
  • It is equal to the Electric potential energy of unit + ve charge at that point.
  • It is a scalar
  • S. I unit is volt

Equipotential Surface

  • A surface on which all points are at the same potential.
  • Electric field is perpendicular to the equipotential surface
  • Work done in moving a charge on the equipotential surface is zero.

Electron Volt

This is the unit of energy in particle physics and is represented as eV.

Charged Particle in Electric Field

  • When a positive test charge is fired in the direction of an electric field
  • It accelerates,
  • Its kinetic energy increases and hence
  • Its potential energy decreases.