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Insulators and Conductors

A conductor is a material that readily allows charge to flow through it, and an insulator is a material that does not readily allow charge to flow. Metals such as silver, copper and aluminium are good conductors, whereas glass and rubber are good insulators.

An electroscope is a device which is used to detect the nature and strength of electric charges on a body.


Description: Description: 97447.png

Coulomb’s Law The force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them, i.e.,
Description: 91651.png
where q1 and q2 are the charges separated by a distance r. Unit of charge is coulomb (C).
K is a constant whose value is 8.887 × 109 Nm2 C−2 and the constant K can also be written as Description: 91662.png
where ε0 is known as the permittivity of free space and has a value 8.8542 × 1012 C2/Nm2.
Coulomb’s law for charges situated in a medium, other than vacuum, is written as Description: 91670.png,
where ε is called the absolute permittivity of the medium: ε = ε0εr, where εr is the relative permittivity of the medium.
Electric Field Every charge will have its own region of influence around it. This region where its electric influence can be detected is said to contain an electric field. Any charge placed in this field experiences an electrostatic force. The intensity of the electric field at a point is the force experienced by a unit positive charge placed at that point.
Electric Field Lines An electric field line is an imaginary line in an electric field along which a free test charge would move when placed in it. The electric field lines originate from a positive charge and end on a negative charge.
A point charge in an electric field experiences a force given by Description: 91679.png, where Description: 91686.png is the field intensity and q is the charge.
Electric Potential Electric potential at a point near the given configuration of charges is the potential energy gained by a unit positive charge in bringing it from infinity to that point. For a point charge q, the electric potential at a distance r from it is given by Description: 91696.png. Potential due to a positive charge is positive, whereas for a negative charge it is negative.
Potential Difference Potential difference between any two points is the work done in moving unit positive charge from one point to the other.
The SI unit of potential difference is Volt. It is measured using voltmeter. Potential difference between any two points is also called voltage.

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