I guess my question has multiple parts. Any help in understanding the questions is appreciated. Assume a single electron in free space. The electron starts moving because of some force applied to it. The source of the force could be pretty much anything, lets say a uniform E-field in X direction. The electron will move on the X axis from left to right and passes the origin (X=0) at arbitrarily chosen time t=0. As we know current is a function of space and time. My question is: 1) What is the current as a function of time at origin? An observer (a sensor) is staring at the origin only. 2) Is the current at origin a multiple of Dirac delta function? This is my initial guess. Then, what would be the value of the multiplier to the Dirac delta function? Like in I = a * D(t), where D(t) is the Dirac delta function. What is multiplier "a" here? 3) If it is a Dirac delta function, it means it contains all frequency components (Fourier transform), isn't it? Including DC and visible frequencies. 4) If it includes DC, it means a portion of the current has been at the origin at all times even before electron reaches there (at negative times). 5) If it includes visible light, it means we should be able to see the light from the moving electron in free space if we stare at origin. 6) One might argue that the flash of light is so short that we cannot see it. What if we send a train of electrons at equi-time intervals (Dirac comb function). Then, we tune the time interval in such a way that one peak in frequency domain happens at a visible frequency. Then, we should see a constant light there. If #2 above is wrong, then all other questions will not be valid. But, if it is right, then it is so strange to me.