# Question about the RHS of Maxwell's equations

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#### sundaram

##### Newbie level 5
In the RHS of maxwell's equations, we have variables like D and B. For minimizing the number of variables, we use the constituent equation like, D = εE and B = µH. why dont we directly write E and H there in Maxwell equations instead of separately specifying them in those constituent equations...? kindly reply me..

#### vicky

##### Full Member level 4
Re: maxwell,'s equations

In linear materials, the polarization density (in coulombs per square meter) and magnetization density (in amperes per meter) are given by:

and the and fields are related to and by:

where as

χe is the electrical susceptibility of the material,

χm is the magnetic susceptibility of the material,

is the electrical permittivity of the material, and

μ is the magnetic permeability of the material

(This can actually be extended to handle nonlinear materials as well, by making ε and μ depend upon the field strength

http://en.wikipedia.org/wiki/Maxwell's_equations

also check it

### sundaram

points: 2

#### sundaram

##### Newbie level 5
Re: maxwell,'s equations

but i think u ve not written the equations there in the reply... could u pls give them...?

#### dineshbabumm

Re: maxwell,'s equations

sundaram said:
In the RHS of maxwell's equations, we have variables like D and B. For minimizing the number of variables, we use the constituent equation like, D = εE and B = µH. why dont we directly write E and H there in Maxwell equations instead of separately specifying them in those constituent equations...? kindly reply me..

Well the original reason is we dont know what is the medium we operate in!

For instance,lets take one of the maxwell equation:

Del X (H) = (dow (D)/dow (t)) + J, where J represent the currents such as source current,drift curret etc which is added for consistency!

Now if u want to replace D by εE, then dow (D)/dow (t) = ε * (down (E)/down (t)) + E * dow (ε)/ dow (t).

We write like this because,we cant assume ε remains constant with time.. That is,the wave in one medium at one time may get into another medium at another time.. So we should not write directly like that!

Hope the answer wil be satisfying for you.. If not,then do ask me more..

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