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G5B04

ELECTRICAL PRINCIPLES · - The decibel; current and voltage dividers; electrical power calculations; sine wave root-mean-square (RMS) values; PEP calculations

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How many watts of electrical power are consumed by a 12 VDC light bulb that draws 0.2 amperes?

  1. A2.4 watts
  2. B24 watts
  3. C6 watts
  4. D60 watts
Why DC power is simply voltage times current, P = E x I. Here 12 volts multiplied by 0.2 amperes gives 2.4 watts. No other formula is needed because both voltage and current are given directly.
Watch out The 24 watt choice is the answer you get by slipping a decimal place, treating the 0.2 A as 2 A; the 60 watt figure comes from dividing 12 by 0.2, which gives resistance in ohms, not power.
P = E x I. Watch the decimal: 0.2 A is one fifth of an amp, so the answer is small.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
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The rest of G5B

  1. G5B01 What dB change represents a factor of two increase or decrease in power?
  2. G5B02 How does the total current relate to the individual currents in a circuit of parallel resistors?
  3. G5B03 How many watts of electrical power are consumed if 400 VDC is supplied to an 800-ohm load?
  4. G5B04 How many watts of electrical power are consumed by a 12 VDC light bulb that draws 0.2 amperes?
  5. G5B05 How many watts are consumed when a current of 7.0 milliamperes flows through a 1,250-ohm resistance?
  6. G5B06 What is the PEP produced by 200 volts peak-to-peak across a 50-ohm dummy load?
  7. G5B07 What value of an AC signal produces the same power dissipation in a resistor as a DC voltage of the same valu…
  8. G5B08 What is the peak-to-peak voltage of a sine wave with an RMS voltage of 120 volts?
  9. G5B09 What is the RMS voltage of a sine wave with a value of 17 volts peak?
  10. G5B10 What percentage of power loss is equivalent to a loss of 1 dB?
  11. G5B11 What is the ratio of PEP to average power for an unmodulated carrier?
  12. G5B12 What is the RMS voltage across a 50-ohm dummy load dissipating 1200 watts?
  13. G5B13 What is the output PEP of an unmodulated carrier if the average power is 1060 watts?
  14. G5B14 What is the output PEP of 500 volts peak-to-peak across a 50-ohm load?
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