G-5
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SUBELEMENT G5 – ELECTRICAL PRINCIPLES
[3 Exam Questions – 3 Groups]
G5A – Reactance; inductance; capacitance; impedance; impedance matching
The opposition to the flow of current in an AC circuit is impedance
Opposition to the flow of alternating current caused by capacitance or inductance is reactance
Reactance causes opposition to the flow of alternating current in an inductor
Reactance causes opposition to the flow of alternating current in a capacitor
An inductor react to AC by as the frequency of the applied AC increases, the reactance increases
A capacitor react to AC by as the frequency of the applied AC increases, the reactance decreases
The source can deliver maximum power to the load when the impedance of an electrical load is equal to the output impedance of a power source, assuming both impedances are resistive
Impedance matching is important so the source can deliver maximum power to the load
Ohm is used to measure reactance
Ohm is used to measure impedance
Insert an LC network between the two circuits describes one method of impedance matching between two AC circuits
To maximize the transfer of power is one reason to use an impedance matching transformer
A transformer, Pi-network and length of transmission line can be used for impedance matching at radio frequencies
G5B – The Decibel; current and voltage dividers; electrical power calculations; sine wave root-mean-square (RMS) values; PEP calculations
Approximately 3 dB represents a two-times increase or decrease in power
Total current relate to the individual currents in each branch of a purely resistive parallel circuit equals the sum of the currents through each branch
How many watts of electrical power are used if 400 VDC is supplied to an 800 ohm load? 200 watts
How many watts of electrical power are used by a 12 VDC light bulb that draws 0.2 amperes? 2.4 watts
How many watts are dissipated when a current of 7.0 milliamperes flows through 1.25 kilohms resistance? Approximately 61 milliwatts
What is the output PEP from a transmitter if an oscilloscope measures 200 volts peak-to-peak across a 50 ohm dummy load connected to the transmitter output? 100 watts
The RMS value is value of an AC signal produces the same power dissipation in a resistor as a DC voltage of the same value
What is the RMS voltage of a sine wave with a value of 17 volts peak? 12 volts
20.5 percent is the power loss would result from a transmission line loss of 1 dB
What is the ratio of peak envelope power to average power for an unmodulated carrier? 1.00
What would be the RMS voltage across a 50 ohm dummy load dissipating 1200 watts? 245 volts
What is the output PEP of an unmodulated carrier if an average reading wattmeter connected to the transmitter output indicates 1060 watts? 1060 watts
What is the output PEP from a transmitter if an oscilloscope measures 500 volts peak-to-peak across a 50 ohm resistive load connected to the transmitter output? 625 watts
G5C – Resistors, capacitors, and inductors in series and parallel; transformers
Mutual inductance causes a voltage to appear across the secondary winding of a transformer when an AC voltage source is connected across its primary winding
What happens if you reverse the primary and secondary windings of a 4:1 voltage step down transformer? The secondary voltage becomes 4 times the primary voltage
A resistor in series should be added to an existing resistor to increase the resistance
What is the total resistance of three 100 ohm resistors in parallel? 33.3 ohms
If three equal value resistors in series produce 450 ohms, what is the value of each resistor? 150 ohms
What is the RMS voltage across a 500-turn secondary winding in a transformer if the 2250-turn primary is connected to 120 VAC? 26.7 volts
What is the turns ratio of a transformer used to match an audio amplifier having 600 ohm output impedance to a speaker having 4 ohm impedance? 12.2 to 1
What is the capacitance of three 100 microfarad capacitors connected in series? 33.3 microfarads
What is the inductance of three 10 millihenry inductors connected in parallel? 3.3 millihenrys
What is the inductance of a 20 millihenry inductor connected in series with a 50 millihenry inductor? 70 millihenrys
What is the capacitance of a 20 microfarad capacitor connected in series with a 50 microfarad capacitor? 14.3 microfarads
A capacitor in parallel should be added to a capacitor to increase the capacitance
An inductor in series should be added to an inductor to increase the inductance
What is the total resistance of a 10 ohm, a 20 ohm, and a 50 ohm resistor connected in parallel? 5.9 ohms
The conductor of the primary winding of many voltage step up transformers is larger in diameter than the conductor of the secondary winding to accommodate the higher current of the primary
What is the value in nanofarads (nF) of a 22,000 pF capacitor? 22 nF
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