In this Physics video lecture in HINDI for class 12 we explained relative permittivity and absolute permittivity of a medium. Relative permittivity of a medium is defined as the ratio of the electrostatic force between two charges placed in vacuum or air (free space) to the electrostatic force between them placed at the same distance in that medium.
ε_r = F/F_m
Where, F is the magnitude of the electrostatic force between two charges placed in vacuum and F_m is the magnitude of the electrostatic force between them in a medium.
e.g., relative permittivity of water is 81, that of kerosene is 2.
Absolute permittivity of free space and is equal to 8.854 ×10^(-12) C^2 N^(-1) m^(-2).
When two charges q_1 and q_2 are placed at a distance r in a medium, the magnitude of electrostatic force between them is
|F ⃗| = 1/(4πε_0 ε_r ) (q_1 q_2)/r^2
Here, ε_r is called the relative permittivity of that medium.
Relative permittivity is also known as dielectric constant.
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Other relevent topics :
Electric Charge : The property of a proton or an electron, which gives rise to electrostatic force between them, is called electric charge .
It is a scalar quantity.
In S.I., its unit is coulomb (C).
A proton possesses +e charge, whereas, an electron possesses -e charge, where, e =1.6 × 10 ^(-19) C.
Additive nature of charge : - The total charge on an object is equal to the algebraic sum of all the electric charges distributed in that object.
If q1, q2, ……….. qn are the charges distributed in an object, then the total charge on that object,
q = q1+ q2+ …….+ qn
Quantization of charge : - The fact that all observable charges are always some integral multiple of elementary charge e, is known as quantization of charge.
Hence, any observable charge,
q = ± n e
Law of conservation of charge :- Law of conservation of charge states that for an isolated system, the net charge always remains constant.
In other words, charge can neither be created nor be destroyed.
Coulomb's Law :
Coulomb's law in electrostatics states that the magnitude of the electrostatic force between two charges is directly proportional to the product of the magnitudes of two charges and inversely proportional to the square of the distance between them.
Coulomb's constant is having value 9 × 10 ^9 Nm^2 C^(-2).
Absolute permittivity of free space and is equal to 8.854 ×10^(-12) C^2 N^(-1) m^(-2).
The principle of superposition : - This principle states that when a number of charges are interacting, the electrostatic force between two charges is not affected by the existence of the other charges and the total electrostatic force on a charge is the vector sum of all the forces due to other charges.
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