A dynamo makes $100$ cycles per second. The frequency of the $AC$ is
A.$100Hz$
B.$200Hz$
C.$50Hz$
D.$400Hz$

Hint:Here we are going to apply the concept of dynamo and frequency and by comparing the frequency of alternative current and frequency of Dynamo, we can solve this problem.

Complete step by step answer:
The electric current which changes its magnitude and direction frequently with respect to time in sinusoidal waveform is called the frequency of alternate current. Whereas the frequency of direct current generates a constant wave form and thus does not change its direction with respect to time. The frequency of direct current is applied for operating electrical and electronics equipment which need a constant voltage and current.
For example, direct current of dynamo is used to operate transistors, mobiles phones, D.C. Generators etc. Similarly, the frequency of Alternating current has a wide range of Application, such as generators for single phase and three phase electrical equipment.
The frequency of the Alternative current and the same as the number of cycles of dynamo per second.
Therefore, mathematically we can write it as,
Frequency of Alternating Current = Number of cycles of Dynamo.
Hence, if a dynamo makes $100$ cycles per second then the frequency of AC is also 100 Hz
Therefore, from the above explanation, the correct option is (A) 100 Hz

Note: A dynamo converts the Alternating Current, generated from Alternating current generator, into a direct current by using a Rectifier.