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.
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