chapter 21
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Chapter 21. Alternating Current Circuits and Electromagnetic Waves Alternating Current Resistor in an AC circuit Capacitor in an AC circuit Inductor in an AC circuit RLC series circuit Resonance Transformer Electromagnetic waves Properties of electromagnetic waves - PowerPoint PPT PresentationTRANSCRIPT
Chapter 21Alternating Current Circuits and Electromagnetic Waves
1. Alternating Current2. Resistor in an AC circuit3. Capacitor in an AC circuit4. Inductor in an AC circuit5. RLC series circuit6. Resonance7. Transformer8. Electromagnetic waves9. Properties of electromagnetic waves10. Doppler effect and electromagnetic waves
AC Circuit What is alternating current? What is an AC circuit?
Resistor in an AC Circuit What is it? The voltage source The concept of phase Behavior of the resistor What is the power
dissipated by the resistor?
What is rms current? Why do we need it? What is the average
power? What about ohm’s law?
Example – rms Current1. For the circuit show, calculate the maximum
current and voltage, rms current and voltage and rms power.
Capacitors in an AC Circuit Behavior of the
capacitor What is the Voltage
and Current relationship?
What is capacitive reactance?
How do I calculate it? How do I use ohm’s
law?
Inductors in an AC Circuit Behavior of the
inductor Voltage and current
relationship What is inductive
reactance? How do I calculate it? How do I apply
ohm’s law?
Example - Inductor
1. In a purely inductive ac circuit as shown, Vmax=100V.
1. If the maximum current is 7.5A at 50 Hz, calculate the inductance L.
2. At what angular frequency ω is the maximum current 2.5 A?
The RLC Series Circuit What is the
current in the circuit?
What about voltage and current relationship?
Phasor Diagrams What is a
phasor? diagram?
How do I use it?
Phasor Diagram for RLC series circuit
What is the maximum Voltage?
What is the phase? What about rms
values?
Impedance of a Circuit What is
impedance? How do I calculate
it? How do I apply
ohms’ law?
Example - RLC Circuit
1. A coil of resistance 35 Ω and inductance 20.5 H is in series with a capacitor and a 200-Vrms, 100-Hz source. The rms current in the circuit is 4.0A.
1. Calculate the capacitance in the circuit.2. What is Vrms across the coil?
Summary of Circuit Elements, Impedance and Phase Angles
Power in an AC Circuit How do I calculate the average
power? What is a power factor? Power losses in a capacitor and an
inductor
Example - RLC Circuit
1. In a certain series RLC circuit, Irms=9.0A, Vrms=180V, and the current leads the voltage by 37°.
1. What is the total resistance in the circuit?2. Calculate the magnitude of the reactance of the
circuit (XL-XC).
Resonance in an AC Circuit What is resonance in
an AC circuit? When does is occur? How do I calculate
resonance frequency? Example of devices
that use resonance
Example - Resonance in an AC Circuit1. Calculate the resonant frequency of a
circuit of negligible resistnace containing an inductance of 40mH and a capacitance of 600pF.
Transformers What is a
transformer? How does it work? How do I use it? What about
power?
Example - Transformers1. An AC adapter for telephone-answering unit
uses a transformer to reduce the line voltage of 120Vrms to a voltage of 9.0 V. The rms current delivered to the answering system is 400mA.
1. If the primary (input) coil in the transformer in the adapter has 240 turns, how many turns are there on the secondary (output) coil?
2. What is the rms power delivered to the transformar? Assume an ideal transformer.
Nikola Tesla 1865 – 1943 Inventor Key figure in
development of AC electricity High-voltage
transformers Transport of electrical
power via AC transmission lines
Beat Edison’s idea of DC transmission lines
Why do we use AC and not DC What would you want to conserve? Why do we have high voltage
transmission lines when our homes only have 120V?
James Clerk Maxwell 1831 – 1879 Electricity and
magnetism were originally thought to be unrelated
in 1865, James Clerk Maxwell provided a mathematical theory that showed a close relationship between all electric and magnetic phenomena
More of Maxwell’s Contributions Electromagnetic theory of light Kinetic theory of gases Nature of Saturn’s rings Color vision Electromagnetic field
interpretation Led to Maxwell’s Equations
Maxwell’s Predictions
Hertz’s Confirmation of Maxwell’s Predictions 1857 – 1894 First to generate and
detect electromagnetic waves in a laboratory setting
Showed radio waves could be reflected, refracted and diffracted
The unit Hz is named for him
Hertz’s Basic Apparatus How does it work? What about resonance
frequency? What is the source for
energy transfer? What are
electromagnetic waves?
How do I measure the speed of the waves?
Electromagnetic Waves Produced by an Antenna Acceleration of charge Antenna
Charges and Fields, Summary
Electromagnetic Waves, Summary
Electromagnetic Waves are Transverse Waves
Properties of EM Waves
The EMSpectrum
Doppler Effect and EM Waves
The light of a moving source is blue/red shifted by
/0 = vr/c
0 = actual wavelength
emitted by the source
Wavelength change due to
Doppler effect
vr = radial velocity
Blue Shift (to higher frequencies)
Red Shift (to lower frequencies)
vr
Example – EM Waves
1. What are the wavelength ranges in
1. AM radio band (540-1600 kHz) and2. The FM radio band (88-108 MHz)?
Example – EM Waves
1. A speeder tries to explain to the police that the yellow warning lights on the side of the road looked green to her because of the Doppler shift. How fast would she have been traveling if yellow light of wavelength of 580 nm had been shifted to green with a wavelength of 560 nm?