Technicians Exam-Electrical Principles

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rledwith
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Technicians Exam-Electrical Principles
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Amateur Radio Technicians Exam - T5 Question Set - Electrical Principles
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  1. T5A01 Electrical current is measured in which of the following units?
    A. Volts
    B. Watts
    C. Ohms
    D. Amperes
    • D. Amperes
    • The basic unit of electric current, a measure of the rate of flow of electrons, is the ampere, abbreviated A. (Current is represented by the symbol I or i in equations.) It is named for Andre Marie Ampere, an early 19th century scientist who studied electricity extensively. [Ham Radio License Manual, page 3-1]
  2. T5A02 Electrical power is measured in which of the following units?
    A. Volts
    B. Watts
    C. Ohms
    D. Amperes
    • B. Watts
    • Power is the rate at which energy is used. The basic unit of electrical power is the watt, or W. (Power is represented by the symbol p in equations.) This unit was named after James Watt, the 18th century inventor of the steam engine. [Ham Radio License Manual, page 3-5]
  3. T5A03 What is the name for the flow of electrons in an electric circuit?
    A. Voltage
    B. Resistance
    C. Capacitance
    D. Current
    • D. Current
    • Electrons flow through the wires and components of an electric circuit. The flow of electrons in an electric circuit is called current. (See question T5A01) [Ham Radio License Manual, page 3-1] *T5A01 - The basic unit of electric current, a measure of the rate of flow of electrons, is the ampere, abbreviated A. (Current is represented by the symbol I or i in equations.) It is named for Andre Marie Ampere, an early 19th century scientist who studied electricity extensively. [Ham Radio License Manual, page 3-1]
  4. T5A04 What is the name for a current that flows only in one direction?
    A. Alternating current
    B. Direct current
    C. Normal current
    D. Smooth current
    • B. Direct current
    • Current that flows in one direction all the time is direct current, abbreviated dc. [Ham Radio License Manual, page 3-5]
  5. T5A05 What is the electrical term for the electromotive force (EMF) that causes electron flow?
    A. Voltage
    B. Ampere-hours
    C. Capacitance
    D. Inductance
    • A. Voltage
    • Voltage is the electromotive force or electric potential that makes electrons move. Voltage is measured in volts, abbreviated as V. Voltage is represented in equations by the symbol E or e or v. [Ham Radio License Manual, page 3-1]
  6. T5A06 How much voltage does a mobile transceiver usually require?
    A. About 12 volts
    B. About 30 volts
    C. About 120 volts
    D. About 240 volts
    • A. About 12 volts
    • Vehicle power systems are usually referred to as “12 volt”, although the actual voltage typically varies from 12 to 15 V. Radios designed to operate from a “12 V” supply may actually work best at the slightly higher voltage of 13.8 V, typical of vehicle power systems with the engine running. Check the equipment manual and be sure your power supply can generate the correct voltage. [Ham Radio License Manual, page 5-14]
  7. T5A07 Which of the following is a good electrical conductor?
    A. Glass
    B. Wood
    C. Copper
    D. Rubber
    • C. Copper
    • In general, most metals make good conductors of electricity because their electrons are relatively free to move in response to an applied voltage. Copper, silver and aluminum are all excellent conductors, while wood, paper and glass are very poor conductors. [Ham Radio License Manual, page 3-4]
  8. T5A08 Which of the following is a good electrical insulator?
    A. Copper
    B. Glass
    C. Aluminum
    D. Mercury
    • B. Glass
    • Most non-metallic materials act as insulators because their electrons are not free to move. That means very little current will flow in response to an applied voltage. Ceramics, glass, paper and plastics are examples of good insulators. [Ham Radio License Manual, page 3-4]
  9. T5A09 What is the name for a current that reverses direction on a regular basis?
    A. Alternating current
    B. Direct current
    C. Circular current
    D. Vertical current
    • A. Alternating current
    • Alternating current, or ac, alternates direction, flowing first in one direction, then in the opposite direction. [Ham Radio License Manual, page 3-5]
  10. T5A10 Which term describes the rate at which electrical energy is used?
    A. Resistance
    B. Current
    C. Power
    D. Voltage
    • C. Power
    • Power is the rate at which energy is used. The basic unit of electrical power is the watt, or W. (Power is represented by the symbol p in equations.) This unit was named after James Watt, the 18th century inventor of the steam engine. [Ham Radio License Manual, page 3-5]
  11. T5A11 What is the basic unit of electromotive force?
    A. The volt
    B. The watt
    C. The ampere
    D. The ohm
    • A. The volt
    • Voltage is the electromotive force or electric potential that makes electrons move. Voltage is measured in volts, abbreviated as V. Voltage is represented in equations by the symbol E or e or v. [Ham Radio License Manual, page 3-1]
  12. T5B01 How many milliamperes is 1.5 amperes?
    A. 15 milliamperes
    B. 150 milliamperes
    C. 1,500 milliamperes
    D. 15,000 milliamperes
    • C. 1,500 milliamperes
    • The prefix “milli” means “divide by 1000,” so “milliamperes” means “divide by 1000 to get amperes.” 1500 milliamperes / 1000 = 1.5 amperes. Similarly, to convert from amperes to milliamperes, multiply by 1000, so 1.5 amperes × 1000 = 1500 milliamperes. [Ham Radio License Manual, page 2-2]
  13. T5B02 What is another way to specify a radio signal frequency of 1,500,000 hertz?
    A. 1500 kHz
    B. 1500 MHz
    C. 15 GHz
    D. 150 kHz
    • A. 1500 kHz
    • Checking each of the possible answers: 1500 kHz × 1000 = 1,500,000 Hz (the correct answer) 1500 MHz × 1,000,000 = 1,500,000,000 Hz (too large, 1,500,000 Hz = 1.5 MHz) 15 GHz × 1,000,000,000 = 1,500,000,000,000 Hz (very much too large, 1,500,000 Hz = 0.0015 GHz) 150 kHz × 1000 = 150,000 Hz (too small) [Ham Radio License Manual, page 2-2]
  14. T5B03 How many volts are equal to one kilovolt?
    A. One one-thousandth of a volt
    B. One hundred volts
    C. One thousand volts
    D. One million volts
    • C. One thousand volts
    • The prefix “kilo” means “multiply by 1000,” so “kilovolts” means “multiply by 1000 to get volts.” 1 kilovolt × 1000 = 1000 volts. [Ham Radio License Manual, page 2-2]
  15. T5B04 How many volts are equal to one microvolt?
    A. One one-millionth of a volt
    B. One million volts
    C. One thousand kilovolts
    D. One one-thousandth of a volt
    • A. One one-millionth of a volt
    • The prefix “micro” means “divide by 1,000,000,” so “microvolts” means “divide by 1,000,000 to get volts.” 1 microvolt / 1,000,000 = 0.000001 V or one-millionth of a volt. [Ham Radio License Manual, page 2-2]
  16. T5B05 Which of the following is equivalent to 500 milliwatts?
    A. 0.02 watts
    B. 0.5 watts
    C. 5 watts
    D. 50 watts
    • B. 0.5 watts
    • The prefix “milli” means “divide by 1000,” so “milliwatts” means “divide by 1000 to get watts.” 500 milliwatts / 1000 = 0.5 W or watts. [Ham Radio License Manual, page 2-2]
  17. T5B06 If an ammeter calibrated in amperes is used to measure a 3000-milliampere current, what reading would it show?
    A. 0.003 amperes
    B. 0.3 amperes
    C. 3 amperes
    D. 3,000,000 amperes
    • C. 3 amperes
    • The prefix “milli” means “divide by 1000,” so “milliwatts” means “divide by 1000 to get watts.” 3000 milliamperes / 1000 = 3 A or amperes. [Ham Radio License Manual, page 2-2]
  18. T5B07 If a frequency readout calibrated in megahertz shows a reading of 3.525 MHz, what would it show if it were calibrated in kilohertz?
    A. 0.003525 kHz
    B. 35.25 kHz
    C. 3525 kHz
    D. 3,525,000 kHz
    • C. 3525 kHz
    • To convert from MHz to kHz, multiply by 1000 because 1000 kHz = 1 MHz. 3.525 × 1000 = 3525 kHz. [Ham Radio License Manual, page 2-2]
  19. T5B08 How many microfarads are 1,000,000 picofarads?
    A. 0.001 microfarads
    B. 1 microfarad
    C. 1000 microfarads
    D. 1,000,000,000 microfarads
    • B. 1 microfarad
    • To convert from picofarads to microfarads divide by 1,000,000, so 1,000,000 picofarads (or pF) = 1 microfarad (or µF). [Ham Radio License Manual, page 2-2]
  20. T5B09 What is the approximate amount of change, measured in decibels (dB), of a power increase from 5 watts to 10 watts?
    A. 2 dB
    B. 3 dB
    C. 5 dB
    D. 10 dB
    • B. 3 dB
    • Radio signals vary dramatically in strength. At the input to a receiver, signals are frequently smaller than one ten-billionth of a watt. When they come out of a transmitter, they’re often measured in kilowatts! Electronic circuits change signal strengths by many factors of 10. These big differences in value make it difficult to compare signal sizes. Enter the decibel, abbreviated dB and pronounced “dee-bee.” The decibel measures the ratio of two quantities as a power of 10. The formula for computing decibels is: dB = 10 log (power ratio) dB = 20 log (voltage ratio). Positive values of dB mean the ratio is greater than 1 and negative values of dB indicate a ratio of less than 1. For example, if an amplifier turns a 5-watt signal into a 10-watt signal, that’s a change of 10 log (10 / 5) = 10 log (2) = 3 dB. [Ham Radio License Manual, page 4-6]
  21. T5B10 What is the approximate amount of change, measured in decibels (dB), of a power decrease from 12 watts to 3 watts?
    A. 1 dB
    B. 3 dB
    C. 6 dB
    D. 9 dB
    • C. 6 dB
    • dB = 10 log (3 / 12) = 10 log (0.25) = –6 dB, so the amount of change is 6 dB (regardless of whether the amount of change is positive or negative). [Ham Radio License Manual, page 4-6]
  22. T5B11 What is the approximate amount of change, measured in decibels (dB), of a power increase from 20 watts to 200 watts?
    A. 10 dB
    B. 12 dB
    C. 18 dB
    D. 28 dB
    • A. 10 dB
    • dB = 10 log (200 / 20) = 10 log (10) = 10 dB [Ham Radio License Manual, page 4-6]
  23. T5C01 What is the ability to store energy in an electric field called?
    A. Inductance
    B. Resistance
    C. Tolerance
    D. Capacitance
    • D. Capacitance
    • The ability to store energy in an electric field is called capacitance and it is measured in farads (F). Capacitors store electrical energy in the electric field created by a voltage between two conducting surfaces (such as metal foil) called electrodes. The electrodes are separated by an insulator called the dielectric. [Ham Radio License Manual, page 3-6]
  24. T5C02 What is the basic unit of capacitance?
    A. The farad
    B. The ohm
    C. The volt
    D. The henry
    • A. The farad
    • The ability to store energy in an electric field is called capacitance and it is measured in farads (F). Capacitors store electrical energy in the electric field created by a voltage between two conducting surfaces (such as metal foil) called electrodes. The electrodes are separated by an insulator called the dielectric. [Ham Radio License Manual, page 3-6]
  25. T5C03 What is the ability to store energy in a magnetic field called?
    A. Admittance
    B. Capacitance
    C. Resistance
    D. Inductance
    • D. Inductance
    • Inductors store magnetic energy in the magnetic field created by current flowing through a wire. This property is called inductance and it is measured in henrys (H). [Ham Radio License Manual, page 3-7]
  26. T5C04 What is the basic unit of inductance?
    A. The coulomb
    B. The farad
    C. The henry
    D. The ohm
    • C. The henry
    • Inductors store magnetic energy in the magnetic field created by current flowing through a wire. This property is called inductance and it is measured in henrys (H). [Ham Radio License Manual, page 3-7]
  27. T5C05 What is the unit of frequency?
    A. Hertz
    B. Henry
    C. Farad
    D. Tesla
    • A. Hertz
    • Each complete back-and-forth sequence of a radio signal (or any oscillating system, such as a pendulum) is called a cycle. The number of cycles per second is the signal’s frequency, represented by a lower-case f. The unit of measurement for frequency is the hertz, abbreviated Hz. One cycle per second is one hertz or 1 Hz. As frequency increases, it becomes easier to use units of kilohertz (1 kHz = 1000 Hz), megahertz (1 MHz = 1000 kHz = 1,000,000 Hz), and gigahertz (1 GHz = 1000 MHz = 1,000,000,000 Hz). [Ham Radio License Manual, page 2-2]
  28. T5C06 What is the abbreviation that refers to radio frequency signals of all types?
    A. AF
    B. HF
    C. RF
    D. VHF
    • C. RF
    • If connected to a speaker, signals below 20 kHz produce sound waves you can hear, so we call them audio frequency or AF signals. Signals that have a frequency greater than 20,000 Hz (or 20 kHz) are radio frequency or RF signals. [Ham Radio License Manual, page 2-3]
  29. T5C07 What is a usual name for electromagnetic waves that travel through space?
    A. Gravity waves
    B. Sound waves
    C. Radio waves
    D. Pressure waves
    • C. Radio waves
    • A radio wave is a combination of an electric and a magnetic field, just like the fields in a capacitor and inductor but spreading out into space like ripples traveling across the surface of water. Because a radio wave is made up of both types of fields, it is called an electromagnetic wave. (See questions T3A07.) [Ham Radio License Manual, page 4-6] *T3A07 - An electromagnetic wave is a combination of an electric and a magnetic field, just like the fields in a capacitor and inductor but spreading out into space like ripples traveling across the surface of water. The wave’s electric and magnetic fields oscillate at the same frequency as the RF current in the transmitting antenna. [Ham Radio License Manual, page 4-6]
  30. T5C08 What is the formula used to calculate electrical power in a DC circuit?
    A. Power (P) equals voltage (E) multiplied by current (I)
    B. Power (P) equals voltage (E) divided by current (I)
    C. Power (P) equals voltage (E) minus current (I)
    D. Power (P) equals voltage (E) plus current (I)
    • A. Power (P) equals voltage (E) multiplied by current (I)
    • Power is the product of voltage and current. As with Ohm’s Law, if you know any two of P, E or I, you can determine the missing quantity as follows: P = E × I or E = P / I or I = P / E. Voltage and current are never combined by adding or subtraction. [Ham Radio License Manual, pages 3-4, 3-5]

  31. T5C09 How much power is being used in a circuit when the applied voltage is 13.8 volts DC and the current is 10 amperes?
    A. 138 watts
    B. 0.7 watts
    C. 23.8 watts
    D. 3.8 watts
    • A. 138 watts
    • Power = voltage × current = 13.8 V × 10 A = 138 W. [Ham Radio License Manual, page 3-5]
  32. T5C10 How much power is being used in a circuit when the applied voltage is 12 volts DC and the current is 2.5 amperes?
    A. 4.8 watts
    B. 30 watts
    C. 14.5 watts
    D. 0.208 watts
    • B. 30 watts
    • Power = voltage × current = 12 V × 2.5 A = 30 W. [Ham Radio License Manual, page 3-5]
  33. T5C11 How many amperes are flowing in a circuit when the applied voltage is 12 volts DC and the load is 120 watts?
    A. 0.1 amperes
    B. 10 amperes
    C. 12 amperes
    D. 132 amperes
    • B. 10 amperes
    • From the equations presented in the explanation of question T5C08, current = power / voltage = 120 W / 12 V = 10 A. [Ham Radio License Manual, page 3-5] *T5C08 - Power is the product of voltage and current. As with Ohm’s Law, if you know any two of P, E or I, you can determine the missing quantity as follows: P = E × I or E = P / I or I = P / E. Voltage and current are never combined by adding or subtraction. [Ham Radio License Manual, page 3-5]
  34. T5D01 What formula is used to calculate current in a circuit?
    A. Current (I) equals voltage (E) multiplied by resistance (R)
    B. Current (I) equals voltage (E) divided by resistance (R)
    C. Current (I) equals voltage (E) added to resistance (R)
    D. Current (I) equals voltage (E) minus resistance (R)
    • B. Current (I) equals voltage (E) divided by resistance (R)
    • Ohm’s Law states that R = E / I. If you know any two of I, E, or R, you can determine the missing quantity as follows: R = E / I, I = E / R, or E = I × R. The drawing in the figure below is a convenient aid to remembering Ohm’s Law in any of these three forms. [Ham Radio License Manual, page 3-4]
  35. T5D02 What formula is used to calculate voltage in a circuit?
    A. Voltage (E) equals current (I) multiplied by resistance (R)
    B. Voltage (E) equals current (I) divided by resistance (R)
    C. Voltage (E) equals current (I) added to resistance (R)
    D. Voltage (E) equals current (I) minus resistance (R)
    • A. Voltage (E) equals current (I) multiplied by resistance (R)
    • Voltage = current × resistance, or E = I × R. (See question T5D01) [Ham Radio License Manual, page 3-4] *T5D01 - Ohm’s Law states that R = E / I. If you know any two of I, E, or R, you can determine the missing quantity as follows:
    • R = E / I, I = E / R, or E = I × R. The drawing in the figure below is a convenient aid to remembering Ohm’s Law in any of these three forms. [Ham Radio License Manual, page 3-4]
  36. T5D03 What formula is used to calculate resistance in a circuit?
    A. Resistance (R) equals voltage (E) multiplied by current (I)
    B. Resistance (R) equals voltage (E) divided by current (I)
    C. Resistance (R) equals voltage (E) added to current (I)
    D. Resistance (R) equals voltage (E) minus current (I)
    • B. Resistance (R) equals voltage (E) divided by current (I)
    • Resistance = voltage divided by current, or R = E / I. (See question T5D01) [Ham Radio License Manual, page 3-4] *T5D01 - Ohm’s Law states that R = E / I. If you know any two of I, E, or R, you can determine the missing quantity as follows:
    • R = E / I, I = E / R, or E = I × R. The drawing in the figure below is a convenient aid to remembering Ohm’s Law in any of these three forms. [Ham Radio License Manual, page 3-4]
  37. T5D04 What is the resistance of a circuit in which a current of 3 amperes flows through a resistor connected to 90 volts?
    A. 3 ohms
    B. 30 ohms
    C. 93 ohms
    D. 270 ohms
    • B. 30 ohms
    • R = E / I = 90 V / 3 A = 30 Ω or ohms. (See question T5D01) [Ham Radio License Manual, page 3-4] *T5D01 - Ohm’s Law states that R = E / I. If you know any two of I, E, or R, you can determine the missing quantity as follows:
    • R = E / I, I = E / R, or E = I × R. The drawing in the figure below is a convenient aid to remembering Ohm’s Law in any of these three forms. [Ham Radio License Manual, page 3-4]
  38. T5D05 What is the resistance in a circuit for which the applied voltage is 12 volts and the current flow is 1.5 amperes?
    A. 18 ohms
    B. 0.125 ohms
    C. 8 ohms
    D. 13.5 ohms
    • C. 8 ohms
    • R = E / I = 12 V / 1.5 A = 8 Ω or ohms. (See question T5D01) [Ham Radio License Manual, page 3-4] *T5D01 - Ohm’s Law states that R = E / I. If you know any two of I, E, or R, you can determine the missing quantity as follows:
    • R = E / I, I = E / R, or E = I × R. The drawing in the figure below is a convenient aid to remembering Ohm’s Law in any of these three forms. [Ham Radio License Manual, page 3-4]
  39. T5D06 What is the resistance of a circuit that draws 4 amperes from a 12-volt source?
    A. 3 ohms
    B. 16 ohms
    C. 48 ohms
    D. 8 ohms
    • A. 3 ohms
    • R = E / I = 12 V / 4 A = 3 Ω or ohms (See question T5D01) [Ham Radio License Manual, page 3-4]
    • *T5D01 - Ohm’s Law states that R = E / I. If you know any two of I, E, or R, you can determine the missing quantity as follows: R = E / I, I = E / R, or E = I × R. The drawing in the figure below is a convenient aid to remembering Ohm’s Law in any of these three forms. [Ham Radio License Manual, R = E / I = 12 V / 4 A = 3 Ω or ohms (See question T5D01) [Ham Radio License Manual, page 3-4] *T5D01 - Ohm’s Law states that R = E / I. If you know any two of I, E, or R, you can determine the missing quantity as follows:
    • R = E / I, I = E / R, or E = I × R. The drawing in the figure below is a convenient aid to remembering Ohm’s Law in any of these three forms. [Ham Radio License Manual, page 3-4]
  40. T5D07 What is the current flow in a circuit with an applied voltage of 120 volts and a resistance of 80 ohms?
    A. 9600 amperes
    B. 200 amperes
    C. 0.667 amperes
    D. 1.5 amperes
    • D. 1.5 amperes
    • I = E / R = 120 V / 80 Ω = 1.5 A or amperes. (See question T5D01) [Ham Radio License Manual, page 3-4] *T5D01 - Ohm’s Law states that R = E / I. If you know any two of I, E, or R, you can determine the missing quantity as follows: R = E / I, I = E / R, or E = I × R. The drawing in the figure below is a convenient aid to remembering Ohm’s Law in any of these three forms. [Ham Radio License Manual, page 3-4]
  41. T5D08 What is the current flowing through a 100-ohm resistor connected across 200 volts?
    A. 20,000 amperes
    B. 0.5 amperes
    C. 2 amperes
    D. 100 amperes
    • C. 2 amperes
    • I = E / R = 200 V / 100 Ω = 2 A or amperes. (See question T5D01) [Ham Radio License Manual, page 3-4] *T5D01 - Ohm’s Law states that R = E / I. If you know any two of I, E, or R, you can determine the missing quantity as follows: R = E / I, I = E / R, or E = I × R. The drawing in the figure below is a convenient aid to remembering Ohm’s Law in any of these three forms. [Ham Radio License Manual, page 3-4]
  42. T5D09 What is the current flowing through a 24-ohm resistor connected across 240 volts?
    A. 24,000 amperes
    B. 0.1 amperes
    C. 10 amperes
    D. 216 amperes
    • C. 10 amperes
    • I = E / R = 240 V / 24 Ω = 10 A or amperes. (See question T5D01) [Ham Radio License Manual, page 3-4] *T5D01 - Ohm’s Law states that R = E / I. If you know any two of I, E, or R, you can determine the missing quantity as follows: R = E / I, I = E / R, or E = I × R. The drawing in the figure below is a convenient aid to remembering Ohm’s Law in any of these three forms. [Ham Radio License Manual, page 3-4]
  43. T5D10 What is the voltage across a 2-ohm resistor if a current of 0.5 amperes flows through it?
    A. 1 volt
    B. 0.25 volts
    C. 2.5 volts
    D. 1.5 volts
    • A. 1 volt
    • E = I × R = 0.5 A × 2 Ω = 1 V or volt. (See question T5D01) [Ham Radio License Manual, page 3-4] *T5D01 - Ohm’s Law states that R = E / I. If you know any two of I, E, or R, you can determine the missing quantity as follows: R = E / I, I = E / R, or E = I × R. The drawing in the figure below is a convenient aid to remembering Ohm’s Law in any of these three forms. [Ham Radio License Manual, page 3-4]
  44. T5D11 What is the voltage across a 10-ohm resistor if a current of 1 ampere flows through it?
    A. 1 volt
    B. 10 volts
    C. 11 volts
    D. 9 volts
    • B. 10 volts
    • E = I × R = 1 A × 10 Ω = 10 V or volts. (See question T5D01) [Ham Radio License Manual, page 3-4] *T5D01 - Ohm’s Law states that R = E / I. If you know any two of I, E, or R, you can determine the missing quantity as follows: R = E / I, I = E / R, or E = I × R. The drawing in the figure below is a convenient aid to remembering Ohm’s Law in any of these three forms. [Ham Radio License Manual, page 3-4]
  45. T5D12 What is the voltage across a 10-ohm resistor if a current of 2 amperes flows through it?
    A. 8 volts
    B. 0.2 volts
    C. 12 volts
    D. 20 volts
    • D. 20 volts
    • E = I × R = 2 A × 10 Ω = 20 V or volts. (See question T5D01) [Ham Radio License Manual, page 3-4] *T5D01 - Ohm’s Law states that R = E / I. If you know any two of I, E, or R, you can determine the missing quantity as follows: R = E / I, I = E / R, or E = I × R. The drawing in the figure below is a convenient aid to remembering Ohm’s Law in any of these three forms. [Ham Radio License Manual, page 3-4]

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