Has such experiment been performed before? Consider a charge of 1C kept a distance of $6*10^8$ m from a detector.
I find electric field due to this charge at detector.
Then, I suddenly earth that charge
and not the time it takes to be detected by detector.
It should be about 2 sec.
Has any similar experiment been performed before.
Such experiment can help to distinguish b/w speed of electromagnetic wave and
speed of electric field propagation.
 A: This has been already studied extensively in the electrodynamics formalism of James Clerk Maxwell and experimentally proved to be correct many times. So magnetic fields and electric fields are unified into a single formalism called Electromagnetism which propagates with constant speed of light in vacuum. This means that the presence or absence of any electric and/or magnetic fields can be felt according to causality. 
A: To earth the charged body does not mean that the electric field of this charges disappears.
To make such a charged body one has to separate some amount of electrons and as a result one get a negative charged body and a positive charged body side by side. So beside the weakness of the electric field of the charged body over such a big distance the angular resolution of your measurement instrument has to be very high  Otherwise you will detect the overlapping fields of both charged bodies.
Of course you can separate the two charged bodies over a big distance and than start the measurement of the very weak over distance electric field. But again, to earth the body to do with the flow of the electrons from this body (or to this body) to an other body. This second body has to be out Of the area, where your instrument scan the charged body. And during the flow of the electrons due to earthing the electric field does not fall to zero immediately, especially if you had a big distance to the ground (which big distance you need to separate the field due to the possible angular resolution of your instrument. 
But much more important is the fact that the electric field of charged particles are theirs intrinsic properties, means this fields could not be switched on not off. They are only separable. In mixed states of protons and electrons their fields don't vanish. 
