2016-E5D: AC and RF energy in real circuits: skin effect; electrostatic and electromagnetic fields; reactive power; power factor; electrical length of conductors at UHF and microwave frequencies
What is the result of skin effect?
As frequency increases, RF current flows in a thinner layer of the conductor, closer to the surface
As frequency decreases, RF current flows in a thinner layer of the conductor, closer to the surface
Thermal effects on the surface of the conductor increase the impedance
Thermal effects on the surface of the conductor decrease the impedance
Why is it important to keep lead lengths short for components used in circuits for VHF and above?
To avoid unwanted inductive reactance
To increase the thermal time constant
To maintain component lifetime
All of these choices are correct
What is microstrip?
Precision printed circuit conductors above a ground plane that provide constant impedance interconnects at microwave frequencies
Lightweight transmission line made of common zip cord
Miniature coax used for low power applications
Short lengths of coax mounted on printed circuit boards to minimize time delay between microwave circuits
Why are short connections necessary at microwave frequencies?
To reduce phase shift along the connection
To increase neutralizing resistance
Because of ground reflections
To reduce noise figure
Which parasitic characteristic increases with conductor length?
In what direction is the magnetic field oriented about a conductor in relation to the direction of electron flow?
In a direction determined by the left-hand rule
In the same direction as the current
In a direction opposite to the current
In all directions; omni-directional
What determines the strength of the magnetic field around a conductor?
The amount of current flowing through the conductor
The resistance divided by the current
The ratio of the current to the resistance
The diameter of the conductor
What type of energy is stored in an electromagnetic or electrostatic field?
What happens to reactive power in an AC circuit that has both ideal inductors and ideal capacitors?
It is repeatedly exchanged between the associated magnetic and electric fields, but is not dissipated
It is dissipated as heat in the circuit
It is dissipated as kinetic energy in the circuit
It is dissipated in the formation of inductive and capacitive fields
How can the true power be determined in an AC circuit where the voltage and current are out of phase?
By multiplying the apparent power times the power factor
By dividing the reactive power by the power factor
By dividing the apparent power by the power factor
By multiplying the reactive power times the power factor
What is the power factor of an R-L circuit having a 60 degree phase angle between the voltage and the current?
How many watts are consumed in a circuit having a power factor of 0.2 if the input is 100-VAC at 4 amperes?
How much power is consumed in a circuit consisting of a 100 ohm resistor in series with a 100 ohm inductive reactance drawing 1 ampere?
What is reactive power?
Wattless, nonproductive power
Power consumed in wire resistance in an inductor
Power lost because of capacitor leakage
Power consumed in circuit Q
What is the power factor of an R-L circuit having a 45 degree phase angle between the voltage and the current?
What is the power factor of an R-L circuit having a 30 degree phase angle between the voltage and the current?
How many watts are consumed in a circuit having a power factor of 0.6 if the input is 200VAC at 5 amperes?
How many watts are consumed in a circuit having a power factor of 0.71 if the apparent power is 500VA?
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