Why does a current flow from positive to negative?
Hint: We have two directions assigned to the current-conventional and electronic-both are important to understand. The conventional direction was adopted way before the discovery of the electronic current and hence it is used. But we do recognize the electronic current as a fundamental concept in physics.
Complete step by step answer: A battery is responsible for the generation of current in a circuit. It sets up a gradient along which the current flows. This gradient occurs due to accumulation of positive and negative charges on each of the terminals of the battery. The current flow is characterized by the flow of electrons. The electrons move from the negative terminal of the battery to the positive terminal of the battery. This is called the electronic current. The direction of the electronic current is thus said to be from negative to positive. Long before, electrons were discovered, we had a knowledge of the protons or the positive charge carriers. So, there was no concept of electronic current. We required a convention that could be followed in solving practical problems and hence, we assumed the direction of current as defined by the motion of the protons. We take the current to be moving from the positive terminal of the battery to the negative terminal of the battery. This is called the conventional current. Hence, the current flows from positive to the negative terminal of the battery
Note: Even though the directions of the actual electronic and the conventional current are different, solving numerical problems and analyzing circuits with the conventional current direction gives the correct results. This happens because all the theorems and results have already incorporated the direction in themselves. We need not redefine the direction of electrons as it is simply the opposite to the conventional current direction.