The frequency of an alternating current is 3 Hz. It implies that
- A.there are 6 cycles/s
- B.there are 3 cycles/s
- C.there are 2 cycles/s
- D.there is only 1 cycle/s
Correct answer
Explanation
The correct answer is B, there are 3 cycles/s. One hertz means one complete cycle per second, so a frequency of 3 Hz means the current completes three full cycles every second.
In alternating current the direction of flow keeps reversing. In one cycle the current rises to a maximum in one direction, falls to zero, rises to a maximum in the opposite direction and returns to zero. So a 3 Hz current reverses direction six times each second, but it completes only three cycles. The unit is named after Heinrich Hertz. Household supply in India is 50 Hz at 230 V, while the USA uses 60 Hz.
A, 6 cycles/s, confuses cycles with reversals of direction; 3 Hz gives 6 reversals but 3 cycles.
C, 2 cycles/s, would be a frequency of 2 Hz.
D, 1 cycle/s, would be a frequency of 1 Hz.
Exam tip: frequency in Hz equals cycles per second; the current changes direction twice in every cycle, so Indian 50 Hz mains reverses 100 times a second.
Practice Questions
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- B.Martin Luther
- C.Johannes Kepler
- D.Copernicus
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- C.Histones are proteins associated with lipids in the cytosol.
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