Quiz time|R2C TECHNOLOGIES

 

Frequency of direct current is _________

(A) zero.

(B) unity.

(C) 50 Hz.

(D) infinity.

Answer: 

option(A)

Reason: 

Direct Current is unidirectional in nature hence frequency will be zero.Alternating current is bidirectional in nature hence it has frequency.

Further justification

Alternating Current (AC)

Alternating Current (AC) flows one way, then the other way, continually reversing direction.

An AC voltage is continually changing between positive (+) and negative (-).

The rate of changing direction is called the frequency of the AC and it is measured in hertz (Hz) which is the number of forwards-backwards cycles per second.

Mains electricity has a frequency of 50Hz mostly but some countries maintain 60Hz also .The primary difference between 50 Hz (Hertz) and 60 Hz (Hertz) is simply that 60 Hz is 20% higher in frequency.Lower the frequency, speed of induction motor and generator will be lower. For example:  With 50 Hz, generator will be running at 3,000 RPM against 3,600 RPM with 60 Hz.

See below for more details of signal properties.

An AC supply is suitable for powering some devices such as lamps and heaters but almost all electronic circuits require a steady DC supply (see below).

AC from a power supply
This shape is called a sine wave.

This triangular signal is AC because it changes
between positive (+) and negative (-).

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Direct Current (DC)

Direct Current (DC) always flows in the same direction, but it may increase and decrease.

A DC voltage is always positive (or always negative), but it may increase and decrease.

Electronic circuits normally require a steady DC supply which is constant at one value or a smooth DC supply which has only a small variation called ripple.

Cells, batteries and regulated power supplies provide steady DC which is ideal for electronic circuits.

Power supplies contain a transformer which converts the mains AC supply to a safe low voltage AC. Then the AC is converted to DC by a bridge rectifier but the output is varying DC which is unsuitable for electronic circuits.

Some power supplies include a capacitor to provide smooth DC which is suitable for less-sensitive electronic circuits, including most of the projects on this website.

Lamps, heaters and motors will work with any DC supply.

Steady DC
from a battery or regulated power supply,
this is ideal for electronic circuits.

Smooth DC
from a smoothed power supply,
this is suitable for some electronics.
 

Varying DC
from a power supply without smoothing,
this is not suitable for electronics.