1. AC Frequency Introduction to Technology

2. Periodic Motion  All waves show periodic motion.  This means that the pattern repeats itself in a regular way.  Other examples of periodic motion are: A swinging pendulum A rotating wheel

3. Frequency  The frequency of any periodic motion tells us how often the motion is repeated.

4. Cycle and Period Recall that a cycle is one complete pattern of a wave. The period (T) is the amount of time required for the wave to complete one full cycle. The period of an AC signal is measured in seconds, or parts of seconds.

5. Frequency and Period  The frequency is related to the period.  Frequency is measured in cycles per second (Hertz).

6. High Frequencies  Many AC electrical signals have high frequencies.  We often use prefixes to help describe these frequencies.  Examples: 1,000 Hz = 1 kilohertz (kHz) 1,000,000 Hz = 1 megahertz (MHZ)

7. High Frequencies = Small Periods  Since,then  This means that a high frequency signal will have a very short period.  Examples: f = 1,000 Hz T = 0.001 s, or 1 millisecond (ms) f = 1,000,000 Hz T = 0.000001 s, or 1 microsecond (µs)

8. Finding frequency with an oscilloscope 2. Count the number of divisions for one cycle. (It’s easiest to count between two crests or troughs.) 6 Divisions 3. Multiply the number of divisions by the TIME/DIV setting of the oscilloscope. 1. Write down the TIME/DIV knob setting from the oscilloscope. TIME/DIV = 2mS 4. Divide 1 by the period to find the frequency. This gives you the Period (T) of the signal

9. Demonstration  This video illustrates how to make the calculations. http://teachertube.com/viewVideo.php?video_id =75193&title=Measuring_ac_frequency_from _an_oscilloscope_

10. Team Assignment  Objectives: Use a function generator to develop a signal with a specific frequency. Use an oscilloscope to measure the frequency of a signal.

11. Lab Connections See equipment connectionsequipment