In the “lab” frame of reference, where the electrons and the charge +Q move towards the right at the same speed, vd, the electrons appear closer together (length contracted) than they are in ...In the “lab” frame of reference, where the electrons and the charge +Q move towards the right at the same speed, vd, the electrons appear closer together (length contracted) than they are in the frame of reference of the electrons (or of the charge +Q, since it is moving with the electrons).