# Coulomb’s law

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[Audio] Hi everyone Today our topic is Coulomb law

Coulomb’s law

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[Audio] Coulomb law states that The force between two point charges is directly proportional to the product of magnitude of charges and inversely proportional to square of distance between them Mathematically Force f is proportional to product of q 1 and q 2 F is proportional to one over r square

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[Audio] F is equal to k Q 1 q 2 by r square Where k is the constant of proportionality And its value depends upon The system of units used And medium between the charges

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[Audio] Coulomb force is a mutual force It means if charge q 1 exert a force on q 2 Then charge q 2 also exert force on q1 In order to determine the direction of force We use unit vector along the line joining The two charges If r 1 2 is the unit vector pointing from the charge Q 1 towards charge q 2 Which shows force on q 2 due to charge q 1 Mathematically F 2 1 is equal to k Q 1 q 2 by r square and R 1 2 is the unit vector that describe the Direction of force Similarly force on charge q 1 due to q 2 is F 1 2 is equal to K Q 1 q2 by r square Where r 2 1 be the unit vector describe Direction of force The two forces are equal in magnitude but Opposite in direction

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[Audio] The constant k can be expressed in terms of permittivity of free space K is equal to one over four pie e not Where e not is equal to Eight point eight five multiply ten raised power minus twelve Coulomb square per newton per meter square Putting values on k So k is equal to Nine multiply ten raised power minus nine Newton metre square per coulomb square

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[Audio] Coulomb law in material media

Coulomb law in material media

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[Audio] It is experimentaly observed that when an insulator Is placed between electric charges it reduces the force Permittivity It is the property of medium which affects the magnitude of force between two point charges. The coulomb force can now be written as F is equal to one over four pie e Q 1 q 2 by r square Where e is the permittivity of medium

It is experimentally observed that when an insulator is placed between electric charges it reduces the force. Permittivity: It is the property of medium which affects the magnitude of force between two point charges. The coulomb force can now be written as

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[Audio] Relative permittivity is defined as The of permittivity of medium material to permittivity of vacuum is called relative permittivity Represented by e r e r is dimensionless and its value is always greater than unity Mathematically e r is equal to e by e not

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