Electric Charges and Fields — Class 12 Physics

Matter carries an intrinsic property called electric charge, which exists in two kinds, positive and negative, and is conserved and quantised as . Like charges repel and unlike charges attract through a force whose magnitude between two point charges in vacuum obeys Coulomb's law . To describe the influence a charge exerts on its surroundings we introduce the electric field , a vector quantity whose direction follows the force on a positive test charge. Field lines give a pictorial map of : they start on positive and end on negative charges, never cross, and crowd together where the field is strong. An electric dipole, two equal and opposite charges separated by a small distance, has a dipole moment and experiences a torque in a uniform field. Electric flux measures the field threading a surface, and Gauss's law states the net flux through any closed surface equals the enclosed charge divided by . Gauss's law gives elegant results for symmetric distributions: the field of an infinite line, an infinite charged sheet, and a uniformly charged spherical shell.