ELECTROSTATICS AND CAPACITANCE By RAPHAEL CHILESHE
Laws of electrostatics
1. Like charges repel
2. Unlike charges attract
Coulombs inverse square law
ELECTROSTATIC FIELD : The region around a charged body represented by lines of force.
Properties of line of force (flux lines)
Electric Flux
Electric flux Density, D
Electric field intensity or Field strength, E
or
Relationship between E and D
Permittivity : Easy with which a medium permits an electric flux to be established in it.
Permittivity of free space or air:
Absolute Permittivity:
Relative Permittivity
Electric Potential and Potential Difference
Potential Difference
Potential Gradient, E
CAPACITOR
CAPACITANCE, C : The propert of a capacitor to store electrical energy in the form of static charge.
How a capacitor retains charge.
(a)
RELATIONSHIP BETWEEN CHARGE, Q and VOLTAGE, V
CAPACITANCE OF A PARALLEL CAPACITOR
DIELECTRIC STRENGHTH
(b)
CAPACITORS IN SERIES
All capacitor have same charge, Q.
EX1: Prove the above formular for series circuit.
Voltage distribution:
CAPACITORS IN PARALLEL
EX2:
Prove the above formular.
PARALLEL PLATE CAPACITOR WITH MULTIPLE PLATES
COMPOSITE
DIELECTRIC CAPACITORS
ENERGY STORED IN A CAPACITOR
EX 3: Derive the above formular.
Current in the capacitor.
Current in the capacitor
OF CAPCITORS
TYPES
CHARGING A CAPACITOR THROUGH RESISTANCE ( GROWTH CURVES)
Decay curve
(b)
Growth curve.
Time constant
INITIAL RATE OF RISE OF CAPACITOR VOLTAGE
DISCHARGING A CAPACITOR THROUGH A RESISTOR
Discharging a capacitor
Decay
Curve
NOTE: Transient time = 4xTime constant = 4RC seconds
Significance of time constant