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Electrostatics. Effects in Everyday Life. Electric & magnetic effects in every day life Electric phenomena may produce magnetic effects and magnetic phenomena may produce electric effects Electromagnetism

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Effects in Everyday Life


Electric & magnetic effects in every day life

    • Electric phenomena may produce magnetic effects and magnetic phenomena may produce electric effects
  • Electromagnetism
    • Study of the effects of electric charges at rest or in motion (Electromagnetic effects )
    • Electromagnetic effects can be explained by MWE
  • Electromagnetic interaction
    • Only between those bodies or particles which have a property called charge
    • Types of interactions (strong, weak, tensile, adhesive)
  • Definition of charge
  • Brief History of Electromagnetic effects

Brief History

  • 900 BC – Greek shepherd ‘Magnus’ (a story about Asia Minor-the region was called as Magnesia)
  • The word magnet has come from Greek word magnitislithosmeaning magnesian stone- later on called as loadstone - Loadstone effect
  • 600 BC – Greek philosopher Thales (Discovered another material called amber (from Greek word elektron) which when rubbed with wool will attract cat fur) – Amber effect
  • 370 BC – Plato (both amber effect and loadstone effect are related with each other and of the same type)
  • 120 AD – Plutarc (Load stone emits exhaltations which pushes air)
  • 1100 AD – Chinese (magnetic needle pointing north-south)

1550 AD – Carden (amber and load stone do not attract in the same way)

  • 1600 AD – Gilbert (Introduced science of magnetism by experimentation) Introduction of other substances that would attract when rubbed e.g., glass, sulphur, wax crystals etc)
  • 1752 AD – Benjamin Franklin (Kite flying in thunder storm)
  • 1780 AD – Galvani (idea of moving charges)
  • 1784 AD – Coulomb (measured the electric force)
  • 1792 AD– Volta introduced battery (copper & zinc separated by material soaked in Brine solution-invented battery)
  • 19th Century – Biot, Savart, Ampere, Oersted, Faraday (relationship between electricity & magnetism)

1864 AD – Maxwell’s contribution & later Hertz experimental evidence

    • Charges residing on objects explain electrostatic effects and dynamics of charges explain magnetic effects
    • Engineering Applications – Laser printer, photocopying, Electrostatic paint spraying

Charge-the basic entity of Electromagnetism

  • Properties of charge
    • Charge is quantized
    • Charge is conserved
  • Existence of two types of charges
    • Plastic rod rubbed with wool----- -ve charge
    • Glass rod rubbed with silk -------- +ve charge

Electrostatic force

    • Qualitative analysis – Shifting of electrons is responsible for electrostatics force
      • The net charge of a body is represented by ‘q’
      • Scalar quantity
      • Units
      • 1 C= ------- electrons
    • Quantitative analysis (measurement of electrostatic force)
      • In order to determine the nature of electrostatic force, the magnitude and direction of electrostatic force is required to be measured
      • Experimental arrangements – Torsion balance

Outcomes of the experiment

    • Mathematical expression of Coulomb force between two point charges
    • Constant ‘K’
    • Properties of Coulomb force
    • Principle of linear superposition
    • Significance of Coulomb’s law
  • Vector form of Coulomb’s Law
  • Example
  • All Examples of Chapter 25 (H-R-K)
  • Problems (25.1 – 25.13)

Coulomb force by continuous charge distribution

  • In many applications electric forces are exerted by charged objects in the form of rods, plates or solids
  • Then how the Coulomb’s law can be applied?
  • Procedure to determine Coulomb force
    • Imagine the division of charge distribution into large number of small charge elements
    • Consider any one of the charge element
    • Express the charge element in terms of charge density & size of charge element

Treating charge element as point charge and determine the force element

    • Determination of direction of force element
    • Calculation of total force
  • Applications
    • Line of charge
    • Ring of charge
    • Disc of charge