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G5C11

ELECTRICAL PRINCIPLES · - Resistors, capacitors, and inductors in series and parallel; transformers

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What is the inductance of a circuit with a 20-millihenry inductor connected in series with a 50-millihenry inductor?

  1. A7 millihenries
  2. B14.3 millihenries
  3. C70 millihenries
  4. D1,000 millihenries
Why Inductors in series add just like resistors in series: L_total = L1 + L2. So 20 mH + 50 mH = 70 mH. The magnetic fields of the coils (assuming no mutual coupling) simply add their opposition to changing current.
Watch out The 14.3 mH choice is the parallel result, from the product-over-sum formula (20 x 50)/(20 + 50), and 1,000 is just the product with no division.
Inductors behave like resistors: series adds, parallel divides. Capacitors are the opposite.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
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The rest of G5C

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  3. G5C03 What is the total resistance of a 10-, a 20-, and a 50-ohm resistor connected in parallel?
  4. G5C04 What is the approximate total resistance of a 100- and a 200-ohm resistor in parallel?
  5. G5C05 Why is the primary winding wire of a voltage step-up transformer usually a larger size than that of the secon…
  6. G5C06 What is the voltage output of a transformer with a 500-turn primary and a 1500-turn secondary when 120 VAC is…
  7. G5C07 What transformer turns ratio matches an antenna's 600-ohm feed point impedance to a 50-ohm coaxial cable?
  8. G5C08 What is the equivalent capacitance of two 5.0-nanofarad capacitors and one 750-picofarad capacitor connected …
  9. G5C09 What is the capacitance of three 100-microfarad capacitors connected in series?
  10. G5C10 What is the inductance of three 10-millihenry inductors connected in parallel?
  11. G5C11 What is the inductance of a circuit with a 20-millihenry inductor connected in series with a 50-millihenry in…
  12. G5C12 What is the capacitance of a 20-microfarad capacitor connected in series with a 50-microfarad capacitor?
  13. G5C13 Which of the following components should be added to a capacitor to increase the capacitance?
  14. G5C14 Which of the following components should be added to an inductor to increase the inductance?
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