Question

The frequency of direct current (DC) is:
$$(A)0Hz$$
$$(B)25Hz$$
$$(C)75Hz$$
$$(D)100Hz$$

Answer 1

Hint: Frequency is the number of cycles that are obtained in a given time period. If a wave alternates between the positive and negative axes, its father produces the definite cycles per second.
A DC is the one-directional flow of charge. DC current-time graph is a straight line, so there are no ripples and hence no cycles.

Complete answer:
In a chemical electric cell, the electric characteristic of the positive and the negative remains the same, i.e it does not change with time. If the current sent from the cell is always one-directional, this direction does not reverse. This current is called the Unidirectional Current. But the value of the current can be increased or decreased with time. This is a steady current. We may show two types of DC by the following current-time graphs:
 

A DC is the one-directional flow of charge. DC current-time graph is a straight line, so there are no ripples and hence no cycles.
The frequency is the number of cycles that are obtained in a given time period. If a wave alternates between the positive and negative axes, it further produces the definite cycles per second.
Since the DC has no cycle it has no frequency i.e frequency of DC is $0Hz$

Hence the right answer is in option A.

Note: Alternating current(AC) and Direct current (DC), these are the types of current.
Alternating current changes its direction with a certain time. It flows in a periodic way or in the cycle. So it has ripples and hence has a frequency. The wave is both in positive and negative axes.