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Subel. ZLB
20 questions
Subelement ZLB

Basic Electrical Theory

Section ZLB07

Power calculations

A transmitter power amplifier requires 30 mA at 300 volt. The DC input power is

  • 300 watt
  • 9000 watt
  • Correct Answer
    9 watt
  • 6 watt
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The DC input power of a transmitter operating at 12 volt and drawing 500 milliamp would be

  • Correct Answer
    6 watt
  • 12 watt
  • 20 watt
  • 500 watt
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When two 500 ohm 1 watt resistors are connected in series, the maximum total power that can be dissipated by both resistors is

  • 4 watt
  • Correct Answer
    2 watt
  • 1 watt
  • 1/2 watt
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When two 1000 ohm 5 watt resistors are connected in parallel, they can dissipate a maximum total power of

  • 40 watt
  • 20 watt
  • Correct Answer
    10 watt
  • 5 watt
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The current in a 100 kilohm resistor is 10 mA. The power dissipated is

  • 1 watt
  • Correct Answer
    10 watt
  • 100 watt
  • 10,000 watt
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A current of 500 milliamp passes through a 1000 ohm resistance. The power dissipated is

  • 0.25 watt
  • 2.5 watt
  • 25 watt
  • Correct Answer
    250 watt
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A 20 ohm resistor carries a current of 0.25 ampere. The power dissipated is

  • Correct Answer
    1.25 watt
  • 5 watt
  • 2.50 watt
  • 10 watt
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If 200 volt is applied to a 2000 ohm resistor, the resistor will dissipate

  • Correct Answer
    20 watt
  • 30 watt
  • 10 watt
  • 40 watt
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The power delivered to an antenna is 500 watt. The effective antenna resistance is 20 ohm. The antenna current is

  • 25 amp
  • 2.5 amp
  • 10 amp
  • Correct Answer
    5 amp
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The unit for power is the

  • ohm
  • Correct Answer
    watt
  • ampere
  • volt
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The following two quantities should be multiplied together to find power

  • resistance and capacitance
  • Correct Answer
    voltage and current
  • voltage and inductance
  • inductance and capacitance
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The following two electrical units multiplied together give the unit "watt"

  • Correct Answer
    volt and ampere
  • volt and farad
  • farad and henry
  • ampere and henry
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The power dissipation of a resistor carrying a current of 10 mA with 10 volt across it is

  • 0.01 watt
  • Correct Answer
    0.1 watt
  • 1 watt
  • 10 watt
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If two 10 ohm resistors are connected in series with a 10 volt battery, the battery load is

  • Correct Answer
    5 watt
  • 10 watt
  • 20 watt
  • 100 watt
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Each of 9 resistors in a circuit is dissipating 4 watt. If the circuit operates from a 12 volt supply, the total current flowing in the circuit is

  • 48 ampere
  • 36 ampere
  • 9 ampere
  • Correct Answer
    3 ampere
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Three 18 ohm resistors are connected in parallel across a 12 volt supply. The total power dissipation of the resistor load is

  • 3 watt
  • 18 watt
  • Correct Answer
    24 watt
  • 36 watt
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A resistor of 10 kilohm carries a current of 20 mA. The power dissipated in the resistor is

  • 2 watt
  • Correct Answer
    4 watt
  • 20 watt
  • 40 watt

By convention, \(P\) is power, \(I\) is current, \(R\) is resistance, and \(E\) is Voltage (Electro-motive force).

The Power Law states: \(P = I \times E\). Ohm's law states that \(E = I \times R\). Combining those to remove E, we get a restatement of the Power Law as \(P = I \times (I \times R)\), or \(P = I^2 \times R\)

So in this case:

\[P = (.02)^2 \times 10,000\] \[P = 0.0004 \times 10,000\]

Thus

\[P = 4 \text{ watts}\]

Last edited by kd7bbc. Register to edit

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A resistor in a circuit becomes very hot and starts to burn. This is because the resistor is dissipating too much

  • current
  • voltage
  • resistance
  • Correct Answer
    power
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A current of 10 ampere rms at a frequency of 50 Hz flows through a 100 ohm resistor. The power dissipated is

  • 500 watt
  • 707 watt
  • Correct Answer
    10,000 watt
  • 50,000 watt
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The voltage applied to two resistors in series is doubled. The total power dissipated will

  • Correct Answer
    increase by four times
  • decrease to half
  • double
  • not change
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