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Electrical Principles - Reactance, Impedance, and Power Calculations

Learn about reactance, impedance, and power calculations in electrical circuits. Understand how to calculate voltage, current, and power using Ohm's Law. Explore the concepts of series and parallel circuits with resistors, capacitors, and inductors.

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Electrical Principles - Reactance, Impedance, and Power Calculations

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  1. WELCOME

  2. ELEMENT 3 SUBELEMENT • SUBELEMENT G1 COMMISSION'S RULES • 5 Exam Questions-5 Groups] 60 Questions • SUBELEMENT G2 OPERATING PROCEDURES • [5 Exam Questions-5 Groups] 59 Questions • SUBELEMENT G3 RADIO WAVE PROPAGATION • [3 Exam Questions-3 Groups] 41 Questions • SUBELEMENT G4 AMATEUR RADIO PRACTICES • [5 Exam Questions-5 groups] 65 Questions • SUBELEMENT G5 ELECTRICAL PRINCIPLES • [3 Exam Questions–3 Groups] 44 Questions • SUBELEMENT G6 CIRCUIT COMPONENTS • [2 Exam Questions–2 Groups] 37 Questions • SUBELEMENT G7 PRACTICAL CIRCUITS • [3 Exam Questions–3 Groups] 38 Questions • SUBELEMENT G8 SIGNALS AND EMISSIONS • [3 Exam Questions–3 Groups] 33 Questions • SUBELEMENT G9 ANTENNAS AND FEEDLINES • [4 Exam Questions–4 Groups] 58 Questions • SUBELEMENT G0 ELECTRICAL AND RF SAFETY • [2 Exam Questions–2 Groups] 27 Questions

  3. G5 -ELECTRICAL PRINCIPLES • 3 Exam Questions • 3 Groups 44 Questions

  4. G5A • Reactance; inductance; capacitance; impedance; impedance matching

  5. Reactance; inductance • 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

  6. Reactance; • An inductor reacts to AC by as the frequency of the applied AC increases, the reactance increases. • As the frequency of the applied AC increases on a capacitor , the reactance decreases.

  7. Impedance • 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.

  8. Impedance matching • 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.

  9. G5B • The Decibel; current and voltage dividers; electrical power calculations; sine wave root-mean-square (RMS) values; PEP calculations

  10. E R I Ohms Law Electromotive Force, VOLTS The flow of Electrons, AMPERES Resistance to current flow, OHMS

  11. Power calculations • The formula: Power (P) equals voltage (E) multiplied by current (I).P = I x E

  12. RMS • The RMS value of an AC signal is the voltage that causes the same power dissipation as a DC voltage of the same value. • For an AC signal with a sine-wave shape, the RMS value is .707 times the peak value. • 12 volts is the RMS voltage of a sine wave with a value of 17 volts peak. • The peak-to-peak value of an AC signal is: • 2 × 1.414 × the RMS value.

  13. dB • The formula for calculating power ratios in dB is: • A(dB) = 10 x log10(P2/P1) • Using this formula, you can see that a two-times increase or decrease in power results in a change of 3 dB. • By rearranging the terms of the equation, you would calculate that a power loss of 20.5 % from a loss of 1 dB.

  14. dB & current • 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.

  15. How many watts of electrical power are used if 400 VDC is supplied to an 800 ohm load? 200 watts • I=400v/800ohm • I=.5a • P=IxE • P=.5a x 400v • P=200w

  16. How many watts of electrical power are used by a 12 VDC light bulb that draws 0.2 amperes? 2.4 watts • P=.2a x 12v • P=2.4w

  17. How many watts are dissipated when a current of 7.0 milliamperes flows through 1.25 kilohms resistance? Approximately 61 milliwatts • E=.000007a x .00125ohm • E=.00000000875v • P=.000007a x .00000000875v • P=61milliw

  18. 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 • Vpep x .707 / 2 =RMS • 200x.707/2= 70.7v • I=E/R • I=70.7/50 • I=1.414 • P=1.414 x 70.7 • P= 99.86w

  19. What is the RMS voltage of a sine wave with a value of 17 volts peak? 12 volts • Vp x .707 =RMS • 17pv x 707=12v

  20. What would be the RMS voltage across a 50 ohm dummy load dissipating 1200 watts? 245 volts • V= √1200w x 50ohm • V= 244.94v

  21. 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 • .707 x 500 / 2 = 176.74v • I=176.74v / 50ohm • I=3.535a • P=I x E • P=3.535 x 176.74 • P=624.77w

  22. G5C • Resistors, capacitors, and inductors in series and parallel; transformers

  23. 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.

  24. Transformers • 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.

  25. Resistors & Capacitor • A capacitor in parallel should be added to a capacitor to increase the capacitance. • A resistor in series should be added to an existing resistor to increase the resistance

  26. Resistors • 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

  27. Transformer • 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 • 120 / 2250 = X / 500 • .053 = X /500 • 500 x .053 =X • 26.66v = X

  28. The turns ratio of a transformer used to match an audio amplifier having a 600-ohm output impedance to a speaker having a 4-ohm impedance is 12.2 to 1. This is a ‘turns ratio’ problem NP = turns on the primary NS = turns on the secondary NP NS ZP ZS = = = 150 = 12.2

  29. Capacitance & Resistance • 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

  30. Capacitance & Resistance • What is the capacitance of a 20 microfarad capacitor connected in series with a 50 microfarad capacitor? • 14.3 microfarads • What is the total resistance of a 10 ohm, a 20 ohm, and a 50 ohm resistor connected in parallel? • 5.9 ohms • What is the value in nanofarads (nF) of a 22,000 pF capacitor? • 22 nF

  31. What is impedance? • A. The electric charge stored by a capacitor • B. The inverse of resistance • C. The opposition to the flow of current in an AC circuit • D. The force of repulsion between two similar electric fields

  32. What is reactance? • A. Opposition to the flow of direct current caused by resistance • B. Opposition to the flow of alternating current caused by capacitance or inductance • C. A property of ideal resistors in AC circuits • D. A large spark produced at switch contacts when an inductor is de-energized

  33. Which of the following causes opposition to the flow of alternating current in an inductor? • A. Conductance • B. Reluctance • C. Admittance • D. Reactance

  34. Which of the following causes opposition to the flow of alternating current in a capacitor? • A. Conductance • B. Reluctance • C. Reactance • D. Admittance

  35. How does an inductor react to AC? • A. As the frequency of the applied AC increases, the reactance decreases • B. As the amplitude of the applied AC increases, the reactance increases • C. As the amplitude of the applied AC increases, the reactance decreases • D. As the frequency of the applied AC increases, the reactance increases

  36. How does a capacitor react to AC? • A. As the frequency of the applied AC increases, the reactance decreases • B. As the frequency of the applied AC increases, the reactance increases • C. As the amplitude of the applied AC increases, the reactance increases • D. As the amplitude of the applied AC increases, the reactance decreases

  37. What happens when the impedance of an electrical load is equal to the output impedance of a power source, assuming both impedances are resistive? • A. The source delivers minimum power to the load • B. The electrical load is shorted • C. No current can flow through the circuit • D. The source can deliver maximum power to the load

  38. Why is impedance matching important? • A. So the source can deliver maximum power to the load • B. So the load will draw minimum power from the source • C. To ensure that there is less resistance than reactance in the circuit • D. To ensure that the resistance and reactance in the circuit are equal

  39. What unit is used to measure reactance? • A. Farad • B. Ohm • C. Ampere • D. Siemens

  40. What unit is used to measure impedance? • A. Volt • B. Ohm • C. Ampere • D. Watt

  41. Which of the following describes one method of impedance matching between two AC circuits? • A. Insert an LC network between the two circuits • B. Reduce the power output of the first circuit • C. Increase the power output of the first circuit • D. Insert a circulator between the two circuits

  42. What is one reason to use an impedance matching transformer? • A. To minimize transmitter power output • B. To maximize the transfer of power • C. To reduce power supply ripple • D. To minimize radiation resistance

  43. Which of the following devices can be used for impedance matching at radio frequencies? • A. A transformer • B. A Pi-network • C. A length of transmission line • D. All of these choices are correct

  44. What dB change represents a two-times increase or decrease in power? • A. Approximately 2 dB • B. Approximately 3 dB • C. Approximately 6 dB • D. Approximately 12 dB

  45. How does the total current relate to the individual currents in each branch of a purely resistive parallel circuit? • A. It equals the average of each branch current • B. It decreases as more parallel branches are added to the circuit • C. It equals the sum of the currents through each branch • D. It is the sum of the reciprocal of each individual voltage drop

  46. How many watts of electrical power are used if 400 VDC is supplied to an 800 ohm load? • A. 0.5 watts • B. 200 watts • C. 400 watts • D. 3200 watts

  47. How many watts of electrical power are used by a 12 VDC light bulb that draws 0.2 amperes? • A. 2.4 watts • B. 24 watts • C. 6 watts • D. 60 watts

  48. How many watts are dissipated when a current of 7.0 milliamperes flows through 1.25 kilohms resistance? • A. Approximately 61 milliwatts • B. Approximately 61 watts • C. Approximately 11 milliwatts • D. Approximately 11 watts

  49. What value of an AC signal produces the same power dissipation in a resistor as a DC voltage of the same value? • A. The peak-to-peak value • B. The peak value • C. The RMS value • D. The reciprocal of the RMS value

  50. What is the RMS voltage of a sine wave with a value of 17 volts peak? • A. 8.5 volts • B. 12 volts • C. 24 volts • D. 34 volts

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