NAGALAND Class 12-science Physics Electric Charges and Fields
Electric ChargeLike charges repel each other and unlike charges attract each other.
Charging by contact: Charge is transferred by touch.
Charging by induction and grounding: Charge is often an efficient way of charging a conductor.
Conductors: Allow the easy passage of charges.
Insulators: Resist the passage of charges.
Coulomb's Law1. Coulomb law: ,where F is directed along the line joining the two charges.
2. Superposition principle: The net resultant force on a charge due to multiple charges is the vector sum of forces due to individual charges.
Electric FieldElectric field due to a charge q is the force F that a unit positive charge q would experience if placed at that point.
Superposition principle: The net electric field at any point due to the multiple charges is the vector sum of the electric field due to each charge at that point.
The electric field produced by a point charge Q at a point
Electric FluxElectric flux for a uniform electric field E through an area vector A equals the product of electric field, area of cross-section and cosine of angle between them.
Electric field lines going out of the surface: Positive flux.
Electric field lines going into the closed surface: Negative flux.
1. Field of an electric dipole in its equatorial plane at a distance y from the centre:
2. Dipole electric field on the axis at a distance x from the centre
Gauss LawDerive Electric field due to: long uniformly charged wire, large plane sheet of uniform charge and uniformly charged spherical shell.
Gold Leaf ElectroscopeCharges on an isolated system are always conserved.
Charging due to contact: Transfer of charge from one body to another due to contact.
Gold-leaf electroscope : An apparatus to detect charge on a body.
Quantization: Electric charge is always an integral multiple of an electronic charge.