Course description

Electric and Magnetic constants:

Ø  In the equations describing electric and magnetic fields and their propagation, three constants are normally used.

Ø  One is the speed of light c, and the other two are the electric permittivity of free space ε0 and the magnetic permeability of free space, μ0.

Ø  The magnetic permeability of free space is taken to have the exact value

This contains the force unit N for Newton and the unit A is the Ampere, the unit of electric current.

With the magnetic permeability established, the electric permittivity takes the value given by the relationship

where the speed of light c is given by 

This gives a value of free space permittivity

Where F for Farad, the unit of capacitance.

The permittivity in practice is often used in the form 

Where C for Coulomb, the unit of electric charge.

The electric permittivity is connected to the energy stored in an electric field. It is involved in the expression for capacitance because it affects the amount of charge which must be placed on a capacitor to achieve a certain net electric field.

The magnetic permeability is connected to the energy stored in a magnetic field. It is involved in the expression for inductance because in the presence of a magnetizable medium, a larger amount of energy will be stored in the magnetic field for a given current through the coil. 

Coulomb's Law

Like charges repel, unlike charges attract.

The electric force acting on a point charge q1 as a result of the presence of a second point charge q2 is given by Coulomb's Law:

where ε0 = permittivity of space

Ø  Coulomb's Law satisfies Newton's third law because it implies that exactly the same magnitude of force acts on q2 .

Ø  Coulomb's law is a vector equation and includes the fact that the force acts along the line joining the charges. Like charges repel and unlike charges attract.

Ø  Coulomb's law describes a force of infinite range which obeys the inverse square law, and is of the same form as the gravity force.

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