Electric Charge and Coulomb’s Law
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Conductors and Insulators: |
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Electrical conductors are the materials in which electric charges move freely, whereas electrical
insulators are the materials in which the electric charges cannot move freely. The substances
such as glass, rubber, and wood etc are the electrical insulators and the materials such as
copper, aluminum, and silver are good conductors of electricity.
Semiconductors are the third type of materials in which the flow of charges occur but not like
that of conductors. The properties of the semiconductors lie in between conductors and
insulators. The examples of such materials are germanium and silicon
etc.
The electric force between two stationary charged particles (i) is inversely proportional to the
square of the separation r between the particles and directed along the line joining them, (ii) is
proportional to the product of the charges on the two particles, and (iii) is
attractive if the charges
are of opposite sign and repulsive if the charges have the same sign. Thus,
the Coulomb’s law
can be expressed as:
Here, ke is called Coulomb’s constant and is given as: ke = 8.9875 × 109 Nm2/C2 = 1/4πε0,
where ε0 is the permittivity for free space and is equal to 8.8542 × 10-12 C22/Nm2.
Force is a vector quantity and since the Coulomb’s law deals with the force between two
charges, this force should be treated accordingly.
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