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Direct Current is a flow of electrons in an conductor from a negative to a positive pole. The flow of electrons is induced by a magnetic field that passes over a metal conductor. Since free electrons in the conductor are charged particles they respond to a change in magenetic field. This is known in physics as Faraday's law of induction which describes the relationship of electric current induced in a conductor by the motion and intensity of an external magnetic field, which is captured in the Maxwell–Faraday equation. One could apply Flemings left hand rule to predict the direction of flow of current in relation to the movement of the direction of the magnetic field - in turn which can be used to determine the positive and negative poles. This encompasses direct current induced by a magenetic field, however it is possible to generate a direct current using chemical reactions, this is what we see in batteries. In batteries the exchange of ions and cations in an electrolyte between an anode and cathode causes the flow of electrons in a conductor. In a battery, current will only flow until the poles reach an equilibrium, or the completion of a chemical reaction - at this point the cathode and anode need to be renewed by recharging. In a battery the flow of electrons flow from the anode to the cathode when charged. Direct current can also occur by photovoltaic incident of photons on a semiconductor, which causes electrons to be displaced in a semiconducting material such as doped silicon. Alternating current is basically direct current that osicillates between changing polarity at a certain frequency - for example at hertz which means that the direction of free electrons changes direction times a second in a conductor.
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