Ch 1Electric Charges and Fields — Class 12 Physics, concept-first.

Electricity begins with a simple observation known since antiquity: a piece of amber, rubbed vigorously with fur or cloth, starts to attract small bits of straw, paper or dry leaves.

What is electric charge? Charge is a fundamental, intrinsic property of certain elementary particles (such as the electron and the proton), just as mass is.

Charles Augustin de Coulomb measured, using a sensitive torsion balance, exactly how the force between two small charged spheres depends on their charge and their separation.

Coulomb's law, as stated, describes the force between exactly two point charges. Real situations almost always involve more than two -- a collection of charged particles, ions in a crystal, or protons…

Coulomb's law and the superposition principle, as stated so far, apply directly only to a finite collection of point charges.

Coulomb's law, as stated in Section 1.3, appears to describe an "action at a distance": charge seems to exert a force on charge instantly, across empty space, with nothing physical passing between the…

Because an electric field cannot be seen directly, Michael Faraday introduced a simple and enduring way of picturing it: the electric field line, a continuous curve drawn in space such that the tangen…

Many physically important charge arrangements are not a single isolated charge but a pair of equal and opposite point charges held a small, fixed distance apart.

Consider a dipole made of charges at point and at point , a distance apart, with centre , and consider a point lying on the extension of the dipole axis beyond the positive charge, at distance from th…

Now consider a point on the dipole's equatorial line -- the perpendicular bisector of the line joining and -- at distance from the centre .

The axial result of Section 1.9 and the equatorial result of Section 1.10 are, in fact, two special cases of a single general formula for the field of a short dipole at a point whose position vector (…

Sections 1.9-1.11 considered the field produced by a dipole. This section instead asks what happens to a dipole when it is placed inside someone else's field -- specifically, a UNIFORM external electr…

Before Gauss's theorem can be stated, one more quantity must be defined precisely: electric flux, the measure of how much of an electric field passes through a given surface.

Gauss's theorem (sometimes called Gauss's law) is one of the four fundamental equations of electromagnetism, and it states an exact, general relationship between the electric flux through any closed s…

The problem. Find the electric field at a perpendicular distance from an infinitely long, thin, straight wire carrying a uniform linear charge density (Section 1.5).

The problem. Find the electric field near an infinite, thin, flat sheet carrying a uniform surface charge density (Section 1.5).

The problem. Find the electric field due to a thin spherical shell of radius carrying a total charge spread uniformly over its surface, both outside the shell and inside it.

This sub-topic built up the WBCHSE Unit 1 account of electric charges and fields in the order the syllabus lists it.

Sample papers and previous-year board questions for this subject.