# Chapter 21 - Chapter 21 Alternating Current Circuits and...

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G. Antar 1 Chapter 21 Alternating Current Circuits and Electromagnetic Waves

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G. Antar 2 O utline AC vs DC Resistors in AC circuits Capacitors in AC circuits Inductance in AC circuits RLC series circuits Power in AC circuits Resonance in AC circuits Transformers Electromagnetic waves
G. Antar 3 AC Circuit Alternating Current (AC) flows one way, then the other way, continually reversing direction. An AC voltage is continually changing between positive (+) and negative (-).

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G. Antar 4 The AC/DC war Thomas Edison, American inventor and businessman, was known as "The Wizard of Menlo Park" and pushed for the development of a DC power network. George Westinghouse, American entrepreneur and engineer, backed financially the development of a practical AC power network. Nikola Tesla, Serbian-American inventor, physicist, and electro- mechanical engineer, was known as "The Wizard of The West" and was instrumental in developing AC networks.
G. Antar 5 AC signals, definitions Amplitude is the maximum voltage reached by the signal. It is measured in volts , V . Peak voltage is another name for amplitude. Peak-peak voltage is twice the peak voltage (amplitude). When reading an oscilloscope trace it is usual to measure peak-peak voltage. Time period ( Τ ) is the time taken for the signal to complete one cycle. It is measured in seconds (s) , but time periods tend to be short so milliseconds (ms) and microseconds (µs) are often used. Frequency is the number of cycles per second. It is measured in hertz (Hz) , but frequencies tend to be high so kilohertz (kHz) and megahertz (MHz) are often used. Frequency: f = 1/

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G. Antar 6 Mathematical expressions of AC V = V ( t ) = V max sin ( ϖ t + φ ) I = I ( t ) = I max sin ( ϖ t ) where ϖ is the angular frequency , ϖ = 2 π f , where f is the (cyclic) frequency. f is the number of complete oscillations per second = 1/T. φ is the phase difference between the voltage and current. The phase is the value of V or I at t = 0.
G. Antar 7 Phases between two sine waves

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G. Antar 8 Other AC signals
G. Antar 9 Recall DC currents Steady DC from a battery or regulated power supply, this is ideal for electronic circuits. Smooth DC from a smoothed power supply, this is suitable for some electronics. Varying DC from a power supply without smoothing, this is not suitable for electronics.

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G. Antar 10 Root Mean Square (RMS) Values The value of an AC voltage is continually changing from zero up to the positive peak, through zero to the negative peak and back to zero again. Clearly for most of the time it is less than the peak voltage, so this is not a good measure of its real effect. •We use the
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## This note was uploaded on 01/06/2012 for the course PHYS 205 taught by Professor Antar during the Spring '09 term at American University of Beirut.

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Chapter 21 - Chapter 21 Alternating Current Circuits and...

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