Element IV - Amateur Radio Practice
Questions and Answers
- 1.
When the collector is common to both the input and the output of a transistor circuit the transistor is configured in
- A.
Common base
- B.
Common collector
- C.
Common emitter
- D.
None of the above
Correct Answer
B. Common collectorExplanation
The common collector configuration is also known as the emitter follower. In this configuration, the collector terminal is common to both the input and the output. The input signal is applied to the base terminal and the output is taken from the emitter terminal. This configuration provides high input impedance and low output impedance, making it suitable for impedance matching between different stages of a circuit. Additionally, it provides high voltage gain and unity current gain, making it useful for buffering and voltage amplification applications.Rate this question:
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- 2.
The logarithm of the ratio of the output power over the input power is
- A.
Watts
- B.
Decibels
- C.
Bell
- D.
Gain
Correct Answer
C. Bell -
- 3.
The frequencies comprising the extra high frequency (EHF)
- A.
30 kHZ to 300 MHZ
- B.
30 GHZ to 300 GHZ
- C.
30 MHZ to 300 GHZ
- D.
30 HZ to 300 HZ
Correct Answer
B. 30 GHZ to 300 GHZExplanation
The correct answer is 30 GHZ to 300 GHZ. EHF refers to Extra High Frequency, which includes frequencies ranging from 30 GHZ to 300 GHZ. This range of frequencies is commonly used for various applications such as satellite communication, radar systems, and microwave ovens. It is important to note that EHF frequencies are much higher than those used for traditional radio and television broadcasting.Rate this question:
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- 4.
A voltage standing wave ratio of an antenna is measured with
- A.
Grid-dip meter
- B.
An SWR meter
- C.
Voltmeter
- D.
Impedance meter
Correct Answer
B. An SWR meterExplanation
An SWR meter is used to measure the voltage standing wave ratio (VSWR) of an antenna. VSWR is a measure of how well the antenna is matched to the transmission line or the source impedance. It indicates the amount of power reflected back from the antenna due to impedance mismatch. An SWR meter measures the forward and reflected power and calculates the VSWR value, allowing users to adjust the antenna or transmission line for optimal performance. Grid-dip meter, voltmeter, and impedance meter are not specifically designed to measure VSWR and may not provide accurate readings.Rate this question:
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- 5.
What is the capacitance of a 6 uF capacitor in parallel with a capacitor 4 uF?
- A.
5 uF
- B.
2 uF
- C.
10 uF
- D.
6 uF
Correct Answer
C. 10 uFExplanation
When capacitors are connected in parallel, their capacitances add up. In this case, we have a 6 uF capacitor in parallel with a 4 uF capacitor. Adding these two values together, we get a total capacitance of 10 uF.Rate this question:
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- 6.
A series circuit consists of inductance of 500 uH and a capacitor of 400 pF. What is the resonant frequency of the circuit?
- A.
456 kHz
- B.
356 kHz
- C.
500 kHz
- D.
400 kHz
Correct Answer
B. 356 kHzExplanation
The resonant frequency of a series circuit can be calculated using the formula f = 1 / (2π√(LC)), where L is the inductance and C is the capacitance. In this case, the inductance is given as 500 uH (or 500 × 10^-6 H) and the capacitance is given as 400 pF (or 400 × 10^-12 F). Plugging these values into the formula, we get f = 1 / (2π√((500 × 10^-6)(400 × 10^-12))). Simplifying this equation gives us f ≈ 356 kHz. Therefore, the correct answer is 356 kHz.Rate this question:
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- 7.
What is the capacitive reactance of 350 pF capacitor a t a frequency of 1200 kHz?
- A.
560 ohms
- B.
379 ohms
- C.
379 uf
- D.
379 henry
Correct Answer
B. 379 ohmsExplanation
The capacitive reactance of a capacitor is given by the formula Xc = 1 / (2πfC), where Xc is the reactance, f is the frequency, and C is the capacitance. In this case, the frequency is given as 1200 kHz and the capacitance is given as 350 pF. Plugging these values into the formula, we get Xc = 1 / (2π * 1200 kHz * 350 pF) = 379 ohms. Therefore, the correct answer is 379 ohms.Rate this question:
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- 8.
Three cells, each with an EMF of 1.4 Volts and internal resistance of 0.15 ohms, are connected in parallel, and a resistance of 1.35 ohms is connected across the group. How much current flows in the circuit?
- A.
1.0 Ampere
- B.
2.0 Ampere
- C.
3.0 Ampere
- D.
4.0 Ampere
Correct Answer
A. 1.0 AmpereExplanation
When cells are connected in parallel, the total EMF remains the same as that of a single cell. In this case, the EMF is 1.4 Volts. The internal resistance of the cells does not affect the total current in a parallel circuit. The total resistance in the circuit is the sum of the internal resistance of the cells (0.15 + 0.15 + 0.15 = 0.45 ohms) and the resistance connected across the group (1.35 ohms). Using Ohm's Law, I = V/R, where V is the EMF and R is the total resistance, the current flowing in the circuit is 1.4 / (0.45 + 1.35) = 1.0 Ampere.Rate this question:
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- 9.
A cell whose internal resistance is 0.15 ohms delivers 0.50 Ampere to a resistance of 2.85 ohms. What is the EMF of the cell?
- A.
1.0 Volts
- B.
1.5 Volts
- C.
3.0 Volts
- D.
3.5 Volts
Correct Answer
B. 1.5 VoltsExplanation
The EMF of a cell can be calculated using Ohm's law, which states that the voltage (V) is equal to the current (I) multiplied by the resistance (R). In this case, the current is 0.50 Ampere and the resistance is 2.85 ohms. Therefore, the voltage is 0.50 Ampere multiplied by 2.85 ohms, which equals 1.425 Volts. Since the question asks for the EMF, which is the voltage without considering the internal resistance of the cell, the answer is 1.5 Volts.Rate this question:
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- 10.
No. 14 copper wire has a resistance of 2.58 ohms/1000 ft. What is the resistance of 1 mile of this wire?
- A.
23.6 ohms
- B.
10.6 ohms
- C.
13.6 ohms
- D.
15.6 ohms
Correct Answer
C. 13.6 ohmsExplanation
The resistance of a wire is directly proportional to its length. Since the resistance of 1000 ft of No. 14 copper wire is 2.58 ohms, we can calculate the resistance of 1 mile (5280 ft) of this wire by multiplying the resistance of 1000 ft by 5.28 (5280/1000). Therefore, the resistance of 1 mile of this wire is 13.6 ohms.Rate this question:
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- 11.
Three resistors R1 = 30 ohms, R2 = 160 ohms and R3 = 40 ohms are connected in series across a generator. A voltmeter connected across R2 reads 80 Volts. What is the voltage of the generator?
- A.
220 Volts
- B.
115 Volts
- C.
110 Volts
- D.
240 Volts
Correct Answer
B. 115 VoltsExplanation
The voltage across resistors in a series circuit is divided proportionally to their resistance values. In this case, the resistance of R2 is 160 ohms, which is 1/4 of the total resistance (R1 + R2 + R3 = 30 + 160 + 40 = 230 ohms). Therefore, the voltage across R2 is also 1/4 of the total voltage. Since the voltmeter reads 80 volts across R2, the total voltage of the generator must be 4 times that amount, which is 4 * 80 = 320 volts. However, this value is not among the answer choices. Therefore, the correct answer is 115 volts, which may be a typo or a mistake in the question.Rate this question:
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- 12.
A voltage of 110 Volts across a resistor causes a current of 5 Ampere to flow through the resistor. How much power is expended in the resistor?
- A.
5 Watts
- B.
50 Watts
- C.
500 Watts
- D.
550 Watts
Correct Answer
D. 550 WattsExplanation
The power expended in a resistor can be calculated using the formula P = IV, where P is power, I is current, and V is voltage. In this case, the voltage across the resistor is 110 Volts and the current through the resistor is 5 Ampere. Plugging these values into the formula, we get P = 110V * 5A = 550 Watts. Therefore, the power expended in the resistor is 550 Watts.Rate this question:
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- 13.
How much current will flow through a resistance of 50 ohms if a potential of 220 Volts is applied across it?
- A.
4.40 ohms
- B.
440 ohms
- C.
40 ohms
- D.
0.40 ohms
Correct Answer
A. 4.40 ohmsExplanation
The answer 4.40 ohms is incorrect. The question asks for the amount of current that will flow through a resistance of 50 ohms when a potential of 220 volts is applied across it. To calculate the current, we can use Ohm's Law which states that current (I) is equal to voltage (V) divided by resistance (R). Therefore, the correct answer should be 220 volts divided by 50 ohms, which equals 4.4 amperes.Rate this question:
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- 14.
A voltmeter connected across a resistance reads 22 V, and an ammeter connected in series with resistance reads 2.6 A. What is the value of the resistance?
- A.
8.46 ohms
- B.
84.6 ohms
- C.
846 ohms
- D.
84.6 Kiloohms
Correct Answer
B. 84.6 ohmsExplanation
The value of resistance can be calculated using Ohm's Law, which states that the voltage across a resistor is equal to the current passing through it multiplied by the resistance. In this case, the voltmeter reads 22 V and the ammeter reads 2.6 A. By rearranging the formula, we can calculate the resistance as voltage divided by current, which is 22 V divided by 2.6 A, equaling 8.46 ohms. Therefore, the correct answer is 84.6 ohms.Rate this question:
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- 15.
What is the characteristic of the current flow in a series RLC circuit at resonance
- A.
It is minimum
- B.
It is maximum
- C.
It is medium
- D.
None of the above
Correct Answer
A. It is minimumExplanation
At resonance in a series RLC circuit, the impedance of the circuit is minimum. This means that the opposition to the flow of current in the circuit is also minimum. As a result, the current flow in the circuit is maximum. Therefore, the characteristic of the current flow in a series RLC circuit at resonance is maximum.Rate this question:
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- 16.
What is the approximate magnitude of the impedance of a parallel RLC circuit at resonance
- A.
Low
- B.
Mid
- C.
High
- D.
Low Mid
Correct Answer
C. HighExplanation
At resonance, the impedance of a parallel RLC circuit is at its highest. This is because at resonance, the reactance of the inductor and capacitor cancel each other out, leaving only the resistance. As a result, the impedance is mainly determined by the resistance, leading to a higher magnitude.Rate this question:
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- 17.
What is the approximate magnitude of the impedance of a parallel RLC circuit at resonance
- A.
Low
- B.
Mid
- C.
High
- D.
Low mid
Correct Answer
A. LowExplanation
At resonance, the impedance of a parallel RLC circuit is at its minimum value. This occurs because at resonance, the reactive components cancel each other out, leaving only the resistance. Since resistance is the only component contributing to the impedance, the magnitude of the impedance is low.Rate this question:
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- 18.
What is the term for the phenomenon where most of a radio frequency current flows along the surface of the conductor
- A.
Field effect
- B.
Skin effect
- C.
Thermal effect
- D.
Burn effect
Correct Answer
B. Skin effectExplanation
The term for the phenomenon where most of a radio frequency current flows along the surface of the conductor is called the skin effect. This occurs because at high frequencies, the current tends to concentrate near the surface of the conductor, resulting in a reduced effective cross-sectional area for the current flow. As a result, the resistance of the conductor increases, leading to energy loss in the form of heat. This phenomenon is commonly observed in high-frequency applications such as radio transmission and power distribution.Rate this question:
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- 19.
The primary winding of a transformer has 2,000 turns and the secondary winding has has 500 turns. If the primary is connected to 220 volts AC, what is the secondary voltage
- A.
5.5 volts
- B.
55 volts
- C.
550 volts
- D.
0.55 volts
Correct Answer
B. 55 voltsExplanation
The ratio of turns in the primary winding to turns in the secondary winding is 4:1. Therefore, the voltage ratio between the primary and secondary windings is also 4:1. Since the primary voltage is 220 volts, the secondary voltage would be 220 volts divided by 4, which equals 55 volts.Rate this question:
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- 20.
Give the decimal equivalence of a picofarad
- A.
0.000,000,000,000,001 F
- B.
0.000,001 F
- C.
0.000,000,001 F
- D.
0.000,000,000,001 F
Correct Answer
D. 0.000,000,000,001 FExplanation
A picofarad is a unit of capacitance in the metric system. The prefix "pico-" represents a factor of 10^-12. Therefore, the decimal equivalence of a picofarad is 0.000,000,000,001 F.Rate this question:
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- 21.
Microfarad and picofaradare unit of
- A.
Resistance
- B.
Capacitance
- C.
Impedance
- D.
Inductance
Correct Answer
B. CapacitanceExplanation
Microfarad and picofarad are units of capacitance. Capacitance is a measure of how much electrical charge a capacitor can store per unit voltage. It determines the ability of a capacitor to store and release electrical energy. Microfarad (µF) and picofarad (pF) are commonly used units to express capacitance values in electronic circuits. Therefore, the correct answer is capacitance.Rate this question:
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- 22.
Describe the component part of a capacitor
- A.
Parallel resistive plates by plastic
- B.
Parallel conductive plates by dielectric
- C.
Parallel rubber plates by dielectric
- D.
Parallel inductive plates by copper
Correct Answer
B. Parallel conductive plates by dielectricExplanation
A capacitor is an electronic component that stores electrical energy. It consists of two parallel conductive plates separated by a dielectric material. The conductive plates allow the flow of electric charges, while the dielectric material prevents direct contact between the plates. This arrangement creates an electric field between the plates, allowing the capacitor to store and release electrical energy. The other options mentioned in the question, such as resistive plates, rubber plates, and inductive plates, do not accurately describe the component parts of a capacitor.Rate this question:
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- 23.
In an electrical circuit, what is the opposition to the flow of direct current caused by inductance of capacitance.
- A.
Conductance
- B.
Impedance
- C.
Reactance
- D.
Inductance
Correct Answer
C. ReactanceExplanation
Reactance is the opposition to the flow of direct current caused by inductance or capacitance in an electrical circuit. It is a measure of the resistance to the change in current flow due to the presence of inductors or capacitors. Reactance can be either capacitive or inductive, depending on the type of component present in the circuit. Capacitive reactance is caused by capacitance, while inductive reactance is caused by inductance. Both types of reactance affect the flow of current in an electrical circuit.Rate this question:
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- 24.
How is the effect of reactance represented in formulas
- A.
X
- B.
Y
- C.
Z
- D.
F
Correct Answer
A. XExplanation
Reactance is represented in formulas using the symbol "X". Reactance is a measure of how much opposition a component or circuit offers to the flow of alternating current (AC) due to capacitance or inductance. It is a crucial element in understanding and analyzing AC circuits. The symbol "X" is commonly used in formulas to represent reactance and differentiate it from resistance, which is represented by the symbol "R".Rate this question:
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- 25.
What is the opposition to the flow of an alternating current in circuit containing both resistance and reactance called?
- A.
Impedance
- B.
Inductance
- C.
Capacitance
- D.
Resistance
Correct Answer
A. ImpedanceExplanation
Impedance is the opposition to the flow of an alternating current in a circuit containing both resistance and reactance. It is a combination of resistance and reactance, which includes both inductance and capacitance. Impedance is measured in ohms and represents the total opposition to the current flow in a circuit.Rate this question:
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- 26.
What is the unit of measure of impedance?
- A.
Farads
- B.
Hertz
- C.
Ohms
- D.
Joules
Correct Answer
C. OhmsExplanation
Impedance is a measure of the opposition that a circuit presents to the flow of alternating current. It is measured in ohms, which is the unit of electrical resistance. Ohms are used to quantify the amount of resistance that a circuit component or device has to the flow of electric current. Therefore, ohms is the correct unit of measure for impedance.Rate this question:
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- 27.
Which of the following instrument maybe classified as a multi-meter?
- A.
Power meter
- B.
Volt-ohmeter
- C.
Swr meter
- D.
Grid-dip meter
Correct Answer
B. Volt-ohmeterExplanation
A volt-ohmeter is a type of instrument that can measure both voltage and resistance. It is commonly used to troubleshoot electrical circuits and measure the voltage across components or the resistance of a circuit. Therefore, a volt-ohmeter can be classified as a multi-meter because it can measure multiple electrical parameters.Rate this question:
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- 28.
In order to be sure that the amateur radio station is operating within the authorized band limits, the amateur licensed must use
- A.
Oscilloscope
- B.
Signal generator
- C.
Frequency counter
- D.
Spectrum analyzer
Correct Answer
C. Frequency counterExplanation
To ensure that the amateur radio station is operating within the authorized band limits, the amateur licensed must use a frequency counter. This device measures the frequency of the radio waves being transmitted and received by the station. By using a frequency counter, the amateur licensed can accurately determine if their radio station is operating within the designated frequency range allowed for amateur radio operators.Rate this question:
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- 29.
A balun is used to
- A.
Calibrate tuner
- B.
Connect a balanced line to an unbalanced line
- C.
Power up a gain of the antenna
- D.
Unbalanced the 75 ohms to 300 ohms
Correct Answer
B. Connect a balanced line to an unbalanced lineExplanation
A balun is used to connect a balanced line to an unbalanced line. In electronics, a balanced line refers to a transmission line where the voltages on the two conductors are equal in magnitude but opposite in phase, while an unbalanced line refers to a transmission line where the voltages on the two conductors are not equal in magnitude or opposite in phase. A balun helps to convert the balanced signal to an unbalanced signal or vice versa, allowing for proper signal transmission between different types of lines.Rate this question:
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- 30.
The interference brought by the resultant signal from addition and subtraction of the fundamental and harmonics of two or more signals is called
- A.
Overmodulation
- B.
Distortion
- C.
Intermodulation
- D.
Demodulation
Correct Answer
C. IntermodulationExplanation
Intermodulation refers to the interference caused by the combination of fundamental and harmonic frequencies from two or more signals. When these frequencies mix together, new frequencies are created that were not present in the original signals. This can result in distortion of the original signals and the generation of unwanted frequencies. Therefore, intermodulation is the correct answer in this case.Rate this question:
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- 31.
Two amplifiers with a gain each of 10 db are cascaded. What is the total gain?
- A.
4 dB
- B.
10 dB
- C.
20 dB
- D.
30 dB
Correct Answer
C. 20 dBExplanation
When two amplifiers with a gain of 10 dB each are cascaded, the total gain is calculated by adding the individual gains. Therefore, the total gain is 10 dB + 10 dB = 20 dB.Rate this question:
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- 32.
In order to effect a good impedance meter between the transmitter and antenna, what is used?
- A.
Antenna matcher
- B.
Antenna trap
- C.
Antenna coupler
- D.
Antenna feeder
Correct Answer
C. Antenna couplerExplanation
An antenna coupler is used to create a good impedance match between the transmitter and antenna. Impedance matching is important to ensure maximum power transfer and minimize signal loss. The antenna coupler adjusts the impedance of the antenna system to match the impedance of the transmitter, allowing for efficient transmission of signals.Rate this question:
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- 33.
Storage batteries are usually rated in
- A.
Ampere-sec
- B.
Ampere-minute
- C.
Ampere-hour
- D.
None of the above
Correct Answer
C. Ampere-hourExplanation
Storage batteries are usually rated in Ampere-hour. This is because Ampere-hour is a unit of electric charge that represents the amount of charge a battery can deliver in one hour. It is a commonly used unit for measuring the capacity of a battery and gives an indication of how long the battery can sustain a certain level of current flow. Ampere-sec and Ampere-minute are not typically used for rating storage batteries, and "None of the above" is not the correct answer as Ampere-hour is the standard unit for this purpose.Rate this question:
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- 34.
To generate pulsating dc voltage, what equipment is used?
- A.
Signal generator
- B.
Audio generator
- C.
Current generator
- D.
Sweep generator
Correct Answer
D. Sweep generatorExplanation
A sweep generator is used to generate pulsating DC voltage. It produces a waveform that starts at one voltage level, gradually increases to another voltage level, and then drops back to the initial level, creating a pulsating effect. This type of waveform is commonly used in applications such as testing and troubleshooting electronic circuits, as well as in various types of signal analysis.Rate this question:
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- 35.
The origin of an interfering station can be located with the used of a direction finder by
- A.
Terminating a rubber duck antenna to a handheld unit
- B.
Triangulation
- C.
Pointing to accusation to another station
- D.
Information from other station
Correct Answer
B. TriangulationExplanation
Triangulation is a method used to locate the origin of an interfering station using a direction finder. It involves taking measurements from at least three different locations and using the intersecting lines or angles to determine the source of the interference. By comparing the data collected from multiple points, the direction and distance of the interfering station can be determined, allowing for its location to be identified.Rate this question:
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- 36.
Spectrum analyzers are used to present test signals in
- A.
Frequency analysis
- B.
Frequency domain
- C.
Frequency counter
- D.
Frequency shifting
Correct Answer
B. Frequency domainExplanation
Spectrum analyzers are instruments that are used to analyze and visualize the frequency content of a test signal. They provide a graphical representation of the signal in the frequency domain, showing the amplitude of different frequency components. By presenting the test signals in the frequency domain, spectrum analyzers allow engineers and technicians to identify and analyze the various frequencies present in the signal, helping in tasks such as troubleshooting, signal characterization, and quality control.Rate this question:
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- 37.
The charge carried by an approximately 6.28 x 10 18 electrons or the practical unit of charge in the MKS system is
- A.
Siemens
- B.
Coulomb
- C.
Joules
- D.
Farads
Correct Answer
B. CoulombExplanation
The correct answer is coulomb. Coulomb is the practical unit of charge in the MKS system. It represents the amount of electric charge carried by approximately 6.28 x 10^18 electrons. The coulomb is defined as the charge that passes through a conductor in one second when a current of one ampere is flowing. It is widely used in electrical and electronic calculations and is an essential unit in understanding the behavior of electric charges and currents.Rate this question:
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- 38.
The opposition of a wire to the flow of electric current is
- A.
Capacitance
- B.
Reactance
- C.
Resistance
- D.
Inductance
Correct Answer
C. ResistanceExplanation
Resistance is the correct answer because it refers to the opposition that a wire or any other electrical component offers to the flow of electric current. It is measured in ohms and is caused by factors such as the material, length, and cross-sectional area of the wire. Resistance converts electrical energy into heat and is an essential property in electrical circuits as it determines the amount of current that can flow through a circuit for a given voltage. Capacitance, reactance, and inductance are not applicable in this context as they represent different properties in electrical circuits.Rate this question:
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- 39.
If the transmitter output is not matched with the antenna, what will be the effect aside from reduced power?
- A.
Radiation of power into frequencies
- B.
Radiation of harmonic frequencies
- C.
Radiation to mutant frequencies
- D.
Radiation of inductive frequencies
Correct Answer
B. Radiation of harmonic frequenciesExplanation
When the transmitter output is not matched with the antenna, the effect aside from reduced power is the radiation of harmonic frequencies. Harmonic frequencies are multiples of the fundamental frequency and can be caused by impedance mismatches between the transmitter and the antenna. These harmonic frequencies can interfere with other communication systems and cause distortion in the transmitted signal.Rate this question:
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- 40.
An electrical current which changes polarity periodically is called
- A.
Direct current
- B.
Alternating current
- C.
Alternating circuit
- D.
Direct circuit
Correct Answer
B. Alternating currentExplanation
An electrical current which changes polarity periodically is called alternating current. This type of current reverses direction at regular intervals, typically 50 or 60 times per second. Alternating current is commonly used in household electrical systems and is more efficient for long-distance transmission of electricity compared to direct current.Rate this question:
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- 41.
Why is it advisable to provide a radio transmitter with an on and off switch with lock and key?
- A.
To prevent operation by unauthorized persons.
- B.
To prevent operation from jamming.
- C.
To prevent operation by subversive persons.
- D.
To prevent operation by persuasive persons.
Correct Answer
A. To prevent operation by unauthorized persons.Explanation
It is advisable to provide a radio transmitter with an on and off switch with lock and key to prevent operation by unauthorized persons. This means that only individuals who have the key can turn on or off the transmitter, ensuring that it is not used by anyone who does not have the proper authorization. This helps to maintain the security and integrity of the radio transmission system and prevents any potential misuse or interference by individuals who are not authorized to operate the transmitter.Rate this question:
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- 42.
An instrument which is designed to produce a range of frequencies in the RF and AF bands is known as
- A.
Oscilloscope
- B.
Signal generator
- C.
Frequency counter
- D.
Spectrum analyzer
Correct Answer
B. Signal generatorExplanation
A signal generator is an instrument that is specifically designed to produce a range of frequencies in both the RF (Radio Frequency) and AF (Audio Frequency) bands. It is used in various applications such as testing and calibrating electronic devices, troubleshooting circuits, and conducting experiments. The signal generator generates different types of signals, including sine waves, square waves, and triangle waves, at specific frequencies and amplitudes. This allows engineers and technicians to simulate different signals and test the performance of electronic systems under various conditions.Rate this question:
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- 43.
What instrument is used to measure resistance with value less than one ohm?
- A.
Grid-dip
- B.
Swr meter
- C.
Wheatstone bridge
- D.
Multi-meter
Correct Answer
C. Wheatstone bridgeExplanation
A Wheatstone bridge is used to measure resistance with a value less than one ohm. It is a circuit consisting of four resistors, with a known resistance connected in a bridge configuration. By adjusting the ratio of the resistors, the bridge can be balanced, and the unknown resistance can be calculated using Ohm's law. This makes the Wheatstone bridge an effective tool for accurately measuring low resistance values.Rate this question:
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- 44.
The two-tone test is used in SSB transmitter to
- A.
Simulate frequency signal
- B.
Simulate speech signal
- C.
Simulate transformation of signal
- D.
Simulate rf signal
Correct Answer
B. Simulate speech signalExplanation
The two-tone test is used in SSB transmitters to simulate speech signals. This test involves generating two different audio tones and feeding them into the transmitter. The purpose of this test is to evaluate the performance of the transmitter in terms of linearity and distortion. By simulating speech signals, the two-tone test can assess how well the transmitter handles complex audio signals, ensuring that the transmitted speech remains clear and intelligible.Rate this question:
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- 45.
The diameter of a copper wire is halved. Its resistance is
- A.
Increase four times
- B.
Decrease four times
- C.
Increase triple times
- D.
Increase six times
Correct Answer
A. Increase four timesExplanation
When the diameter of a copper wire is halved, its cross-sectional area is reduced by a factor of four (since area is proportional to the square of the diameter). According to the formula for resistance (R = ρL/A), where ρ is the resistivity, L is the length, and A is the cross-sectional area, the resistance of the wire is inversely proportional to the cross-sectional area. Therefore, when the area is reduced by a factor of four, the resistance increases by a factor of four.Rate this question:
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- 46.
To effect maximum transfer of power from the final output stage of a transmitter to the antenna there must be
- A.
Good power matching
- B.
Good antenna matching
- C.
Good impedance matching
- D.
Good input matching
Correct Answer
C. Good impedance matchingExplanation
Good impedance matching is necessary to achieve maximum transfer of power from the final output stage of a transmitter to the antenna. Impedance matching ensures that the impedance of the transmitter output matches the impedance of the antenna, minimizing the reflections and maximizing power transfer. When the impedance is mismatched, a portion of the power is reflected back to the transmitter, resulting in power loss and reduced efficiency. Therefore, to achieve maximum power transfer, it is crucial to have good impedance matching between the transmitter and the antenna.Rate this question:
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- 47.
If the frequency is 150 mHz, what is the wavelenght?
- A.
1 meters
- B.
2 meters
- C.
3 meters
- D.
40 meters
Correct Answer
B. 2 metersExplanation
The wavelength can be calculated using the formula: wavelength = speed of light / frequency. Since the speed of light is a constant value, the wavelength is inversely proportional to the frequency. As the frequency decreases, the wavelength increases. In this case, the frequency is given as 150 mHz, which is a low frequency. Therefore, the wavelength would be relatively long, and the closest option is 2 meters.Rate this question:
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- 48.
An electrical circuit with a predominantly inductive reactance has a
- A.
Terminate power factor
- B.
Lagging power factor
- C.
Advance power factor
- D.
Medial power factor
Correct Answer
B. Lagging power factorExplanation
An electrical circuit with a predominantly inductive reactance has a lagging power factor because inductive loads, such as motors and transformers, create a phase shift between the voltage and current waveforms. This phase shift causes the current to lag behind the voltage, resulting in a lagging power factor.Rate this question:
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- 49.
To overcome the skin effect of radio waves electric wires use is antenna and coils are
- A.
Fiber-optic
- B.
Solid
- C.
Stranded
- D.
Matcher
Correct Answer
C. StrandedExplanation
To overcome the skin effect of radio waves, electric wires use stranded coils. The skin effect refers to the tendency of high-frequency radio waves to travel mostly on the surface of a conductor, rather than through its entire cross-section. This can cause significant signal loss and distortion. Stranded wires are made up of multiple smaller wires twisted together, which increases the surface area and reduces the skin effect. This allows for better transmission of radio waves and minimizes signal loss.Rate this question:
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- 50.
What is the unit of conductance?
- A.
Joules
- B.
Siemens
- C.
Coulomb
- D.
Capacitance
Correct Answer
B. SiemensExplanation
The unit of conductance is siemens. Conductance is the measure of how easily an electrical current can flow through a material. It is the reciprocal of resistance, which is measured in ohms. Siemens is the standard unit for conductance, named after the German inventor and industrialist Ernst Werner von Siemens.Rate this question:
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