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COULOMB’S
LAW
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INTRODUCTION
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| The magnitude of the force of attraction or repulsion between two electric charges at rest was studied by Charles Coulomb. He formulated a law ,known as "COULOMB'S LAW". | ||||
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STATEMENT
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According
to Coulomb's law:
The electrostatic force of attraction or repulsion between two point charges
is directly proportional to the product of
charges.
The electrostatic force of attraction or repulsion between two point charges
is inversely proportional to the square of
distance between them. |
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MATHEMATICAL
REPRESENTATION OF COULOMB'S LAW
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| Consider two point charges q1 and q2 placed at a distance of r from each other. Let the electrostatic force between them is F. | ||||
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| According to the first part of the law: | ||||
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| According to the second part of the law: | ||||
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| Combining above statements: | ||||
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---------------------(I) |
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| Where k is the constant of proportionality. | ||||
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VALUE
OF K
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| Value of K is equal to 1/4pe0 | ||||
| where eo is permittivity of free space .Its volume is 8.85 x 10-12 c2/Nm2. | ||||
| Thus in S.I. system numerical value of K is 8.98755 x 109 Nm2c-2. | ||||
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OTHER
FORMS OF
COULOMB'S LAW |
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| Putting the value of K = 1/4pe0 in equation (i) | ||||
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FORCE
IN THE PRESENCE OF DIELECTRIC MEDIUM
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| If the space between the charges is filled with a non conducting medium or an insulator called "dielectric", it is found that the dielectric reduces the electrostatic force as compared to free space by a factor (er) called DIELECTRIC CONSTANT. It is denoted by er . This factor is also known as RELATIVE PERMITTIVITY. It has different values for different dielectric materials. | ||||
| In the presence of a dielectric between two charges the Coulomb's law is expressed as: | ||||
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VECTOR
FORM OF
COULOMB'S LAW |
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| The magnitude as well as the direction of electrostatic force can be expressed by using Coulomb's law by vector equation: | ||||
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Where
is the force exerted by q1 on q2 and 
is the unit vector along the line joining the two charges from q1
to q2. |
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| For latest information , free computer courses and high impact notes visit : www.citycollegiate.com | ||||