Class 12 Physics

1.1 Charge, and its three rules Like charges repel and unlike charges attract. Charge is additive, conserved and quantised. 1.2 Coulomb's law The force between two point charges is proportional to their product and to 1/r². 1.3 Force from many charges The total force on a charge is the vector sum of the forces each other charge exerts alone. 1.4 The electric field The field is the force per unit charge at each point. A charge q in a field E feels F = qE. 1.5 Field lines and flux Field lines show the field’s direction and strength; flux Φ = EA cos θ measures the field through a surface. 1.6 The electric dipole Equal and opposite charges a small distance apart. In a uniform field: no net force, but a torque pE sin θ. 1.7 Gauss's law The flux out of any closed surface equals the enclosed charge divided by ε₀.