Current is defined by “rate of change of charge”. If this is the only definition of current then how come direct current is not always 0 according to the definition of current because in dc rate of change of charge is 0 i.e. it doesn't change with time?
Ans: The answer is actually very simple. Let’s use an analogy and that is speed which is similar to current by basic definition i.e. these both are rate of change of something.
Speed = distance/time
For example: speed = 40 km/hr
That means, say your bike is covering the distance with the above speed. So, it will cover a distance of 40 km in one hour. Now, to understand the concept completely let’s go to the 2 hour. If we see the 2nd hour then we will find out that your bike has covered now total of 80 km and that happened in the period of 2 hour. So, the total distance covered is doubled i.e. from 40 km to 80 km but if you see you will find that the speed is still constant no matter how many hours have passed i.e. the rate of change of distance with respect to time is constant while total distance covered is changing with time with the constant speed.
So, it is only the total distance which is actually changing with time and not the speed. Similarly, in electronics it’s the total charge which actually changes (total charge i.e. total number of electrons passed through a wire) with time with the constant current in dc.
