Electrical Charges and Fields Class 12 Notes Physics Chapter 1

Chapter at a Glance

1. Coulomb’s law: The force between two point charges q1 and q2 at rest and placed at a separation r in vacuum or free space is given by

7. The electric field (E) due to a line of charge is proportional to 1/r
8. The electric field (E) due to the uniformly charged flat sheet is constant at all points.
9. Electric field intensity due to an electric dipole

10. An electric field line is an imaginary line or curve drawn through a region of space so that its tangent at any point is in the direction of the electric field vector at that point. Two electric field lines can never intersect. Field lines start at a positive charge and end. at a negative charge.

11. The electric field is uniform in a region, if (a) the number of lines of force crossing the unit area normally, is the same at all points and (b) the lines of force are parallel. The first condition (a) makes the magnitude of the field to be the same, while the second condition (b) makes the direction of the field to be the same at all points.

12. If a cube is placed in a uniform electric field the net flux through it will be zero. This also follows from Gauss’s theorem.

13. Electric flux over an area is equal to the total number of electric field lines crossing this area.
Electric flux through small area element ds is given b

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