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# constant-voltage

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constant-voltage

FCC Commercial Element 3 Question Pool (approved 25 June 2009)

Subelement A Principles: 8 Key Topics, 8 Exam Questions

Key Topic 1: Electrical Elements

3-1A1 The product of the readings of an AC voltmeter and AC ammeter is called:

A. Apparent power.

B. True power.

C. Power factor.

D. Current power.

3-1A2 What is the basic unit of electrical power?

A. Ohm.

B. Watt.

C. Volt.

D. Ampere.

3-1A3 What is the term used to express the amount of electrical energy stored in an electrostatic field?

A. Joules.

B. Coulombs.

C. Watts.

D. Volts.

3-1A4 What device is used to store electrical energy in an electrostatic field?

A. Battery.

B. Transformer.

C. Capacitor.

D. Inductor.

3-1A5 What formula would determine the inductive reactance of a coil if frequency and coil inductance are

known?

A. X = ?f L L

B. X = 2?f L L

C. X = 1 / 2?f C L

D. X = 1 / R2+X2 L

3-1A6 What is the term for the out-of-phase power associated with inductors and capacitors?

A. Effective power.

B. True power.

C. Peak envelope power.

D. Reactive power.

Answer Key: 3-1A1: A 3-1A2: B 3-1A3: A 3-1A4: C 3-1A5: B 3-1A6: D

2009 FCC Commercial Element 3 Question Pool (approved 25 June 2009) Page1

Key Topic 2: Magnetism

3-2A1 What determines the strength of the magnetic field around a conductor?

A. The resistance divided by the current.

B. The ratio of the current to the resistance.

C. The diameter of the conductor.

D. The amount of current.

3-2A2 What will produce a magnetic field?

A. A DC source not connected to a circuit.

B. The presence of a voltage across a capacitor.

C. A current flowing through a conductor.

D. The force that drives current through a resistor.

3-2A3 When induced currents produce expanding magnetic fields around conductors in a direction that opposes the original magnetic field, this is known as:

A. Lenz’s law.

B. Gilbert's law.

C. Maxwell’s law.

D. Norton’s law.

3-2A4 The opposition to the creation of magnetic lines of force in a magnetic circuit is known as:

A. Eddy currents.

B. Hysteresis.

C. Permeability.

D. Reluctance.

3-2A5 What is meant by the term “back EMF”?

A. A current equal to the applied EMF.

B. An opposing EMF equal to R times C (RC) percent of the applied EMF.

C. A voltage that opposes the applied EMF.

D. A current that opposes the applied EMF.

3-2A6 Permeability is defined as:

A. The magnetic field created by a conductor wound on a laminated core and carrying current.

B. The ratio of magnetic flux density in a substance to the magnetizing force that produces it.

C. Polarized molecular alignment in a ferromagnetic material while under the influence of a magnetizing

force.

D. None of these.

Answer Key: 3-2A1: D 3-2A2: C 3-2A3: A 3-2A4: D 3-2A5: C 3-2A6: B

2009 FCC Commercial Element 3 Question Pool (approved 25 June 2009) Page2

Key Topic 3: Materials

3-3A1 What metal is usually employed as a sacrificial anode for corrosion control purposes?

A. Platinum bushing.

C. Zinc bar.

D. Brass rod.

3-3A2 What is the relative dielectric constant for air?

A. 1

B. 2

C. 4

D. 0

3-3A3 Which metal object may be least affected by galvanic corrosion when submerged in seawater?

A. Aluminum outdrive.

B. Bronze through-hull.

C. Exposed lead keel.

D. Stainless steel propeller shaft.

3-3A4 Skin effect is the phenomenon where:

A. RF current flows in a thin layer of the conductor, closer to the surface, as frequency increases.

B. RF current flows in a thin layer of the conductor, closer to the surface, as frequency decreases.

C. Thermal effects on the surface of the conductor increase the impedance.

D. Thermal effects on the surface of the conductor decrease the impedance.

3-3A5 Corrosion resulting from electric current flow between dissimilar metals is called:

A. Electrolysis.

B. Stray current corrosion.

C. Oxygen starvation corrosion.

D. Galvanic corrosion.

3-3A6 Which of these will be most useful for insulation at UHF frequencies?

A. Rubber.

B. Mica.

C. Wax impregnated paper.

Answer Key: 3-3A1: C 3-3A2: A 3-3A3: D 3-3A4: A 3-3A5: D 3-3A6: B

2009 FCC Commercial Element 3 Question Pool (approved 25 June 2009) Page3

Key Topic 4: Resistance, Capacitance & Inductance

3-4A1 What formula would calculate the total inductance of inductors in series?

A. L = L / L T12

B. L = L + L T12

C. L = 1 / L + L T12

D. L = 1 / L x L T12

3-4A2 Good conductors with minimum resistance have what type of electrons?

A. Few free electrons.

B. No electrons.

C. Some free electrons.

D. Many free electrons.

3-4A3 Which of the 4 groups of metals listed below are the best low-resistance conductors?

A. Gold, silver, and copper.

B. Stainless steel, bronze, and lead.

C. Iron, lead, and nickel.

D. Bronze, zinc, and manganese.

3-4A4 What is the purpose of a bypass capacitor?

A. It increases the resonant frequency of the circuit.

B. It removes direct current from the circuit by shunting DC to ground.

C. It removes alternating current by providing a low impedance path to ground.

D. It forms part of an impedance transforming circuit.

3-4A5 How would you calculate the total capacitance of three capacitors in parallel?

A. C = C+ C / C - C + C. T1 2123

B. C = C + C + C. T123

C. C = C+ C / C x C + C. T1 2123

D. C = 1 / C+1 / C + 1 / C. T123

3-4A6 How might you reduce the inductance of an antenna coil?

B. Add more core permeability.

C. Reduce the number of turns.

D. Compress the coil turns.

Answer Key: 3-4A1: B 3-4A2: D 3-4A3: A 3-4A4: C 3-4A5: B 3-4A6: C

2009 FCC Commercial Element 3 Question Pool (approved 25 June 2009) Page4

Key Topic 5: Semi-conductors

3-5A1 What are the two most commonly-used specifications for a junction diode?

A. Maximum forward current and capacitance.

B. Maximum reverse current and PIV (peak inverse voltage).

C. Maximum reverse current and capacitance.

D. Maximum forward current and PIV (peak inverse voltage).

3-5A2 What limits the maximum forward current in a junction diode?

A. The peak inverse voltage (PIV).

B. The junction temperature.

C. The forward voltage.

D. The back EMF.

3-5A3 MOSFETs are manufactured with THIS protective device built into their gate to protect the device from

static charges and excessive voltages:

A. Schottky diode.

B. Metal oxide varistor (MOV).

C. Zener diode.

D. Tunnel diode.

3-5A4 What are the two basic types of junction field-effect transistors?

A. N-channel and P-channel.

B. High power and low power.

C. MOSFET and GaAsFET.

D. Silicon FET and germanium FET.

3-5A5 A common emitter amplifier has:

A. Lower input impedance than a common base.

B. More voltage gain than a common collector.

C. Less current gain than a common base.

D. Less voltage gain than a common collector.

3-5A6 How does the input impedance of a field-effect transistor compare with that of a bipolar transistor?

A. An FET has high input impedance; a bipolar transistor has low input impedance.

B. One cannot compare input impedance without first knowing the supply voltage.

C. An FET has low input impedance; a bipolar transistor has high input impedance.

D. The input impedance of FETs and bipolar transistors is the same.

Answer Key: 3-5A1: D 3-5A2: B 3-5A3: C 3-5A4: A 3-5A5: B 3-5A6: A

2009 FCC Commercial Element 3 Question Pool (approved 25 June 2009) Page5

Key Topic 6: Electrical Measurements

3-6A1 An AC ammeter indicates:

A. Effective (TRM) values of current.

B. Effective (RMS) values of current.

C. Peak values of current.

D. Average values of current.

3-6A2 By what factor must the voltage of an AC circuit, as indicated on the scale of an AC voltmeter, be

multiplied to obtain the peak voltage value?

A. 0.707

B. 0.9

C. 1.414

D. 3.14

3-6A3 What is the RMS voltage at a common household electrical power outlet?

A. 331-V AC.

B. 82.7-V AC.

C. 165.5-V AC.

D. 117-V AC.

3-6A4 What is the easiest voltage amplitude to measure by viewing a pure sine wave signal on an oscilloscope?

A. Peak-to-peak.

B. RMS.

C. Average.

D. DC.

3-6A5 By what factor must the voltage measured in an AC circuit, as indicated on the scale of an AC voltmeter,

be multiplied to obtain the average voltage value?

A. 0.707

B. 1.414

C. 0.9

D. 3.14

3-6A6 What is the peak voltage at a common household electrical outlet?

A. 234 volts.

B. 117 volts.

C. 331 volts.

D. 165.5 volts.

Answer Key: 3-6A1: B 3-6A2: C 3-6A3: D 3-6A4: A 3-6A5: C 3-6A6: D

2009 FCC Commercial Element 3 Question Pool (approved 25 June 2009) Page6

Key Topic 7: Waveforms

3-7A1 What is a sine wave?

A. A constant-voltage, varying-current wave.

B. A wave whose amplitude at any given instant can be represented by the projection of a point on a wheel rotating at a uniform speed.

C. A wave following the laws of the trigonometric tangent function.

D. A wave whose polarity changes in a random manner.

3-7A2 How many degrees are there in one complete sine wave cycle?

A. 90 degrees.

B. 270 degrees.

C. 180 degrees.

D. 360 degrees.

3-7A3 What type of wave is made up of sine waves of the fundamental frequency and all the odd harmonics?

A. Square.

B. Sine.

C. Cosine.

D. Tangent.

3-7A4 What is the description of a square wave?

A. A wave with only 300 degrees in one cycle.

B. A wave whose periodic function is always negative.

C. A wave whose periodic function is always positive.

D. A wave that abruptly changes back and forth between two voltage levels and stays at these levels for equal amounts of time.

3-7A5 What type of wave is made up of sine waves at the fundamental frequency and all the harmonics?

A. Sawtooth wave.

B. Square wave.

C. Sine wave.

D. Cosine wave.

3-7A6 What type of wave is characterized by a rise time significantly faster than the fall time (or vice versa)?

A. Cosine wave.

B. Square wave.

C. Sawtooth wave.

D. Sine wave.

Answer Key: 3-7A1: B 3-7A2: D 3-7A3: A 3-7A4: D 3-7A5: A 3-7A6: C

2009 FCC Commercial Element 3 Question Pool (approved 25 June 2009) Page7

Key Topic 8: Conduction

3-8A1 What is the term used to identify an AC voltage that would cause the same heating in a resistor as a corresponding value of DC voltage?

A. Cosine voltage.

B. Power factor.

C. Root mean square (RMS).

D. Average voltage.

3-8A2 What happens to reactive power in a circuit that has both inductors and capacitors?

A. It is dissipated as heat in the circuit.

B. It alternates between magnetic and electric fields and is not dissipated.

C. It is dissipated as inductive and capacitive fields.

D. It is dissipated as kinetic energy within the circuit.

3-8A3 Halving the cross-sectional area of a conductor will:

A. Not affect the resistance.

B. Quarter the resistance.

C. Double the resistance.

D. Halve the resistance.

3-8A4 Which of the following groups is correct for listing common materials in order of descending conductivity?

A. Silver, copper, aluminum, iron, and lead.

B. Lead, iron, silver, aluminum, and copper.

C. Iron, silver, aluminum, copper, and silver.

D. Silver, aluminum, iron, lead, and copper.

3-8A5 How do you compute true power (power dissipated in the circuit) in a circuit where AC voltage and current are out of phase?

A. Multiply RMS voltage times RMS current.

B. Subtract apparent power from the power factor.

C. Divide apparent power by the power factor.

D. Multiply apparent power times the power factor.

3-8A6 Assuming a power source to have a fixed value of internal resistance, maximum power will be transferred to the load when:

A. The load impedance is greater than the source impedance.

B. The load impedance equals the internal impedance of the source.

C. The load impedance is less than the source impedance.

D. The fixed values of internal impedance are not relative to the power source.

Answer Key: 3-8A1: C 3-8A2: B 3-8A3: C 3-8A4: A 3-8A5: D 3-8A6: B

2009 FCC Commercial Element 3 Question Pool (approved 25 June 2009) Page8

Subelement B Electrical Math: 10 Key Topics, 10 Exam Questions, 3 Drawings

Key Topic 9: Ohm’s Law-1

3-9B1 What value of series resistor would be needed to obtain a full scale deflection on a 50 microamp DC meter with an applied voltage of 200 volts DC?

A. 4 megohms.

B. 2 megohms.

C. 400 kilohms.

D. 200 kilohms.

3-9B2 Which of the following Ohms Law formulas is incorrect?

A. I = E / R

B. I = R / E

C. E = I x R

D. R = E / I

3-9B3 If a current of 2 amperes flows through a 50-ohm resistor, what is the voltage across the resistor?

A. 25 volts.

B. 52 volts.

C. 200 volts.

D. 100 volts.

3-9B4 If a 100-ohm resistor is connected across 200 volts, what is the current through the resistor?

A. 2 amperes.

B. 1 ampere.

C. 300 amperes.

D. 20,000 amperes.

3-9B5 If a current of 3 amperes flows through a resistor connected to 90 volts, what is the resistance?

A. 3 ohms.

B. 30 ohms.

C. 93 ohms.

D. 270 ohms.

3-9B6 A relay coil has 500 ohms resistance, and operates on 125 mA. What value of resistance should be connected in series with it to operate from 110 V DC?

A. 150 ohms.

B. 220 ohms.

C. 380 ohms.

D. 470 ohms.

Answer Key: 3-9B1: A 3-9B2: B 3-9B3: D 3-9B4: A 3-9B5: B 3-9B6: C

2009 FCC Commercial Element 3 Question Pool (approved 25 June 2009) Page9

Key Topic 10: Ohm’s Law-2

3-10B1 What is the peak-to-peak RF voltage on the 50 ohm output of a 100 watt transmitter?

A. 70 volts. C. 140 volts.

B. 100 volts. D. 200 volts.

3-10B2 What is the maximum DC or RMS voltage that may be connected across a 20 watt, 2000 ohm resistor?

A. 10 volts. C. 200 volts.

B. 100 volts. D. 10,000 volts.

3-10B3 A 500-ohm, 2-watt resistor and a 1500-ohm, 1-watt resistor are connected in parallel. What is the maximum voltage that can be applied across the parallel circuit without exceeding wattage ratings?

A. 22.4 volts. C. 38.7 volts.

B. 31.6 volts. D. 875 volts.

3-10B4 In Figure 3B1, what is the voltage drop across R1?

A. 9 volts. C. 5 volts.

B. 7 volts. D. 3 volts.

3-10B5 In Figure 3B2, what is the voltage drop across R1?

A. 1.2 volts. C. 3.7 volts.

B. 2.4 volts. D. 9 volts.

3-10B6 What is the maximum rated current-carrying capacity of a resistor marked “2000 ohms, 200 watts”?

A. 0.316 amps. C. 10 amps.

B. 3.16 amps. D. 100 amps.

Answer Key: 3-10B1: D 3-10B2: C 3-10B3: B 3-10B4: C 3-10B5: D 3-10B6: A

2009 FCC Commercial Element 3 Question Pool (approved 25 June 2009) Page10

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