Is electric current frame dependent? I came across a question in which an observer moves parallel to a current carrying wire(say 2A) with drift velocity(in the same direction as electrons) and then it has been asked what will be the average velocity of electrons with respect to the observer. The answer to this is given zero. In next question, it is asked what will be current with respect to the observer to which answer is given 2A. I'm not able to comprehend the reason for this.
 A: To answer the first question; when suppose the electrons are moving rightwards with drift velocity $v$ and you( the observer ) are also moving rightwards with velocity $v$ then to you the electrons will seem stationary. ( Just like if you are on a car moving at suppose 50 km/h and another car beside you is traveling at 50 km/h that car will look as if it's standing still to you). Thus the relative velocity is zero.
Thus the electrons on average should remain stationary to the observer but remember this that the positive charges in the wire (of nuclei of metal atoms) are stationary to an outside observer so they appear to move backwards with respect to observer. Thus there is a backward flow of positive charge of the same magnitude per unit time( backward flow of positive charge is equivalent to a forward flow of electrons) so the current still remains +2A.
A: So here's my explanation:
The current basically depends on the drift velocity. And the drift velocity is calculated with respect to the conductor, or with respect to the atoms in the conductor. So when you move with the same speed as the electrons, the velocity wrt to you might change, but it remains the same wrt to the conductor. Hence, the current remains the same.
