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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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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 • 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