Why high voltages use in electric car operation?

Answer 1

Actually, the 12 and sometimes 24 volts used in car operation is not very high at all (Your wall probably gives you 112 volts). I think what you're actually asking about is why is the current so large. The answer lies in the transfer of power which is related to current through p=i2 *r where r is the resistance, but also equal to p = i*v which means that the current and voltage (which is called potential) are inversely related. Since the relationship of power to potential is p = v2/r, for a given amount of power available in a battery, more will be able to be used if the current is what dominates. And so, we have cars with 12v (sometimes 24) and 45 or even 90 amp.s (an amp. is the measure of current).

If what you're getting at is why is the power supplied by the battery so large, it's only actual use is to turn the starter motor (which is cranking the entire engine from cold to running), after that, the engine could be self sustaining as long as their is a connection there.

But I wrote a little off topic there. The primary reason why electric cars and power lines have high voltage and low current (again they are inversely proportional) until right before use is that power loss over a length of wire is proportional to the square of the current, but only linear with respect to the potential (ploss = i2*v).