Question

In an A.C. circuit in 1-second current reduces to zero value 120 times. Hence, the frequency of the A.C. current is ______ Hz.
A). 50
B). 100
C). 60
D). 120

Answer 1

We know, in one time period or one cycle the current reduces to zero value twice. This means the current reduces to zero value twice when the frequency is 1Hz. So, now we have to find what will be the frequency when the current reduces to zero value 120 times.

Complete step-by-step solution:

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A.C. circuits are circuits, which function using alternating current. In an A.C. circuit, neither the magnitude nor the direction of current and voltage is constant. They keep varying at regular intervals of time. These are used for both domestic and industrial purposes.
It is known that during one time period current reduces to zero value twice. It is mentioned above that in 1-second current reduces to zero value 120 times. Thus, it can be written as,
When the frequency is 1 current reduces to zero twice, so x will be the frequency when the current reduces to zero 120 times.
$\therefore x= \dfrac {120}{2}$
$\therefore x=60$
Thus, the frequency of the A.C. current is 60Hz.
Hence, the correct answer is option C i.e. 60.

Note: The temporal frequency in India is 50Hz. While in the USA, it is 60Hz. Frequencies of 50Hz require a voltage of 220-240V but the frequency of 60Hz requires less voltage nearly 100V. This 220V power supply can be proved harmful to humans, but the 110V power supply is less harmful. Frequency below 50Hz has its disadvantages. If it is below 50Hz, then we can see the lamp going on and off. But for 50Hz, the time cycle is of 10ms which means the lamp goes off and on every 10ms. Thus, we cannot see the flickering of the bulb.