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How will 2 charged bodies act when the separation medium between them is water ?

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up vote 2 down vote accepted

Indeed, Water has a relative permittivity, but quite a large value of $\epsilon_r\approx80$. Also, It's an electric dipole (i.e.) It could align in the direction of applied non-uniform (oscillating) electric field dissipating its potential energy in the form of heat which is not necessary here. But, it'd be necessary in your future topics in Electrostatics... 'Cause it's the basic principle of Microwave oven.

Attractive (in case of unlike charges) or repulsive force (like charges) between two point charges $q_1$ and $q_2$ in a medium is given by, $$F=\frac{q_1q_2}{4\pi\epsilon_0\epsilon_rr^2}$$

Note: The above force is only for charges situated in a single medium. For a container, we'd have to include the permittivity of air (surroundings), the material of container (the interface) and that of water. Electric lines propagate through all these media. Hence, the net electric field (or force) would be different...

Thanks to @Claudius for reminding me of that...

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This, however, assumes a constant value $\epsilon_r$ over the whole of space and therefore does not apply here if the ‘water container’ is not infinite. – Claudius Oct 11 '12 at 16:46
" It could align in the direction of applied electric field dissipating its potential energy in the form of heat" i would like to know more about this. what should i type in google? and also, does that mean that the temperature of the water will rise? – Abdelrahman Esmat Oct 11 '12 at 16:57
@CrazyBuddy: Your formula for $E$ requires $\epsilon_r$ to be constant over all of space (since the electric field will extend everywhere and the sum of all electric field lines builds up the force on the charges). However, if you just put ‘a bucket of water’ between two electric charges, $\epsilon_r$ is not constant: it is $\approx 80$ within the water and $\approx 1$ outside. Therefore, you will need a more complicated formula effectively integrating over all of space and taking into account the value of $\epsilon_r$ at each point in space. – Claudius Oct 11 '12 at 17:24
The bucket’s walls, of course, have infinitesimal width. – Claudius Oct 11 '12 at 17:44
@AbdelrahmanEsmat: Hello Abdel, Don't think that the applied $E$ would necessarily have to increase temperature of water. It won't evolve heat unless there exists an oscillating or non-uniform electric field... I'd always suggest Hyperphysics for beginners... – Waffle's Crazy Peanut Oct 11 '12 at 17:50

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