Types of current
There are two distinct types of electric currents that we encounter in our everyday life: direct current (dc) and alternating current (ac).
We know current in electrical circuits is due to the motion of positive charge from higher potential to lower potential or electron from lower to higher electrical potential. Electrons move from negative terminal of the battery to positive of the battery. Battery is used to maintain a potential difference between the two ends of the wire. Battery is one of the sources for dc current. The dc is due to the unidirectional flow of electric charges. Some other sources of dc are solar cells, thermocouples etc. e graph depicting the direct current is shown in Fig. 2.19.
Many electronic circuits use dc. Some examples of devices which work on dc are cell phones, radio, electric keyboard, electric vehicles etc.
If the direction of the current in a resistor or in any other element changes its direction alternately, the current is called an alternating current. The alternating current varies sinusoidally with time. is variation is characterised by a term called as frequency. Frequency is the number of complete cycle of variation, gone through by the ac in one second. In ac, the electrons do not flow in one direction because the potential of the terminals vary between high and low alternately. us, the electrons move to and fro in the wire carrying alternating current. It is diagrammatically represented in Fig. 2.20.
Domestic supply is in the form of ac. When we want to use an electrical device in dc, then we have to use a device to convert ac to dc. The device used to convert ac to dc is called rectifier. Colloquially it is called with several names like battery eliminator, dc adaptor and so on. The device used to convert dc in to ac is called inverter. The symbols used in ac and dc circuits are shown in Fig. 2.21.
The voltage of ac can be varied easily using a device called transformer. The ac can be carried over long distances using step up transformers. The loss of energy while distributing current in the form of ac is negligible. Direct current cannot be transmitted as such. The ac can be easily converted into dc. Generating ac is easier than dc. The ac can produce electromagnetic induction which is useful in several ways.
Electroplating, Electro refining, electrotyping can be done only using dc. Electricity can be stored only in the form of dc.