QUESTION: Although I am not a beginner in electronics, I still don't grasp the meaning of 'Frequency'in electronics.apparantly, frequency is the number of complete oscillations. however, I am highly confuse whenever I heard this saying, "the frequency is 69Hz,158KHz..." does it means the quantity oscillate 69Hz or 158kHz per seconds, and what does the phrase 'per seconds' mean? since oscillations does not cease, then how can ones know the specific rate of frequency. please sir, enlighten me!
ANSWER: Hz is a symbol for 'cycles/sec' or rate of change. It is named in honor of Heinrich Hertz an early physicist who did much work with electromagnetic wave analysis and observation.
So, you can use "Hz" and "Cycles/Sec" interchangeably.
K or k is a symbol for 1000. It is shortcut for numbering of large and small quantities.
M or m is the symbol for million or 1,000,000. etc.
Therefore, in your example, 158kHz equals 158,000 cycles/second.
Mostly, in speaking of sinewaves, such as electric power, sine wave oscillators or function generators the term Hz implies that is rate of alternating signal. It can sometimes refer to pulses or events per second.
If you look at a sinewave signal on an oscilloscope, for example, the X axis on the scope screen is time and the Y axis is amplitude of the sine wave.
The youtube given below shows how frequency of a continuous waveform is measured.
Hope this helps, but if you are still confused let me know.
---------- FOLLOW-UP ----------
QUESTION: with respest, sir, the answer is not corresponded with the question. once again, my question goes like this: for instance, the frequency of alternating current(a.c) is 5OHz. does it means the current will be changing 5O cycle-per-seconds? what does the phrase 'per-seconds' mean? Again, when a quantity changes such as a.c, it moves back and forth without ceasing. then how can I know the specific number of oscillations(the frequency)?
Oh, you did watch the youtube? That's about as clear as it gets.
50 cycles per second means exactly that; 50 cycles each second. If you counted them physically there would be 50 repeats each second.
If you ran the marathon at the rate of 10 mph or 10 miles per hour it means you would go 10 miles in one hour. Is that not clear enough?
Alternating current or voltage is continuous and counting the cycles per second is by observing the repeating cycles and counting how many times it repeats or cycles each second.
For example, dc or direct current is 0 Hz or 0 cycles per second it is non-repeating. 1 Hz or 1 cycle in one second is one repeat or cycle each second. 10 Hz is 10 times each second. 100 Hz is 100 times each second. 1000 Hz is 1000 repeats per second. Can it be any more clear?
The you tube was to give you an example of how it is actually measured or observed. It is the classic method of learning about fundamental electricity concepts.
Hope this helps.