LAB_7 - Time Varying 1 - Lab 7 Time Varying Signals I The...

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Lab 7 83 Time Varying Signals I Summary Alternating current (AC) is used everyday in all aspects of life. It is the most common form of delivery of electrical power due to some of its characteristics, such as ease of transmission, conversion and reliability. The voltage at your wall receptacle is AC, that is, the voltage alternates in time as a sinuso- idal waveform. Electric power companies in North America provide voltage and currents which have a sinusoidal waveform with a frequency of 60 cycles per second (60 Hz). This energy is used in a great variety of commercial and domestic applications. Many appliances that plug into the wall socket run directly on AC while others convert the AC into direct current (DC) by use of electronic circuits. Many other types of time varying signals are used in various fields of engineering. This experiment is intended to introduce you to the basic characteristics of sine waves, square waves, triangular waves, and other time varying signals. Educational Objectives After performing this experiment, students should be able to: 1. Measure AC voltage and demonstrate its properties. 2. Use a function generator and an oscilloscope. 3. Measure the period and frequency of sine, square and triangular waves. 4. Measure peak-to-peak and rms values of sine, square and triangular waves. Background Information AC signals change in a periodic fashion. When describing such a signal, it is necessary to indicate both its amplitude and frequency. Consider a resistor with a value of 10 Ohms. If we apply a potential dif- ference of 10V across the resistor we will produce a current of 1 amp according to Ohm’s Law V = IR . However, if we were to reverse the position of the terminals, the resulting current would have the same magnitude as before but would travel in the reverse direction. An AC voltage source behaves in the same manner. The potential reverses repeatedly. Often this change is done in a continuous manner. If we were to apply 10V AC across the above resistor, the voltage across the element would not be constant. Instead, its value would decrease to –10V and then increase back to +10V. This process would be repeated as long as we apply the AC voltage. There are some impor- tant considerations which should be mentioned here. 1. When we say that the voltage change is continuous we mean that, in changing its value from +10V to –10V and back again, the voltage will take on every intermediate value. For example, there will The impetus is much quicker than the water for it often happens that the wave flees the place of its creation, while the water does not; like the waves made in a field of grain by the wind, where we see the waves running across the field while the grain remains in place. - Leonardo da Vinci
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Lab 7 84 be an instant at which the potential difference is zero. (We shall see, however, that in the case of a square wave, the voltage change is not continuous.) 2. A voltage of –10V signifies that the polarity of the potential difference is opposite to that of a +10V signal. Accordingly, the current would flow in the opposite direction. This convention can be com-
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This note was uploaded on 12/16/2011 for the course ENGR 102 taught by Professor Cattell during the Fall '10 term at Community College of Philadelphia.

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LAB_7 - Time Varying 1 - Lab 7 Time Varying Signals I The...

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