MM0704, Lesson 1
In the preceding formula, if time is in seconds, the frequency will be in hertz; if the time is in microseconds, the
frequency will be in megahertz. If the time is given in microseconds but it is desirable to have the frequency in hertz,
then the formula can be written in this manner (instead of changing the microseconds to a fractional part of a second):
P represents the time for one cycle. For example, find the frequency of a square wave if the switch in figure 1-19A is
left in position A for 2,500 sec and in position B for 2,500 sec. The period for one cycle is the sum of two
alternations or 5,000 sec. Using the second formula,
If the frequency is known but the period for one cycle is needed, rewrite the formula as follows:
If the frequency of a square wave is 250 Hz, what is the time for one cycle?
When the period for one cycle of a square wave is 4,000 sec, the time for each alternation is 2,000 sec. An
alternation is the time the switch is in one position, either A or B in figure 1-19A.
To find out what happens when a square wave is applied to a series RC circuit look at figure 1-20. A square wave
having a frequency of 250 Hz is applied to an RC circuit. Since the maximum voltage of the square wave is 50 V, the
instant the square wave is applied to the RC circuit the applied voltage Ea will be 50 V. This 50 V input lasts for one
alternation, 2,000 sec.
Figure 1-20. Sample RC Circuit.