B-005
Subelement B-005
Section B-005-006
Section B-005-006
Why would a large size resistor be used instead of a smaller one of the same resistance?
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Correct AnswerFor greater power dissipation
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For better response time
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For higher conductance
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For less impedance in the circuit
Remember that power is voltage times current, P = E * I. A resistor dissipates power into heat. A resistor can only dissipate so much power without burning up: i.e., its power rating. Larger resistors can dissipate more heat.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
A load requires 12 volts DC at 5 amperes. What is the minimum required power transformer rating?
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17 watts
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Correct Answer60 watts
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2.4 watts
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6 watts
P = E * I, power is voltage times current, watts = volts * amperes. 12 volts * 5 amperes = 60 watts [ V DC = volts in a Direct Current circuit ]
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
What is the DC input power of a transmitter operating at 12 volts and drawing 500 milliamperes?
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24 watts
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600 watts
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Correct Answer6 watts
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60 watts
When two 500-ohm 1-watt resistors are connected in series, the maximum total power that can be dissipated by the resistors is:
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4 watts
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1 watt
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0.5 watts
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Correct Answer2 watts
This is about POWER RATING, not resistance. Two identical resistors can safely dissipate TWICE as much power as only one. [ Yes, total resistance will be twice as much, but that is immaterial here ]
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
When two 500-ohm 1-watt resistors are connected in parallel, they can dissipate a maximum total power of:
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4 watts
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Correct Answer2 watts
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0.5 watts
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1 watt
This is about POWER RATING, not resistance. Two identical resistors can safely dissipate TWICE as much power as only one. [ Yes, total resistance will be half, but that is immaterial here ]
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
If the voltage applied to two resistors in series is doubled, how much will the total power change?
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Decrease to half
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Decrease to one quarter
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Double
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Correct AnswerIncrease four times
P = E * I, power is voltage times current, watts = volts * amperes. Given the proportional relation of current versus voltage stated by Ohm's Law, if you double voltage in a circuit, current will double. Power is voltage times current, if both double, power has quadrupled ( 4 times more ).
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
Which of these combinations of resistors could make up a 50-ohm dummy load capable of safely dissipating 5 watts?
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Ten quarter-watt 500-ohm resistors in parallel
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Two 2-watt 25-ohm resistors in series
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Correct AnswerFour 2-watt 200-ohm resistors in parallel
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Two 5-watt 100-ohm resistors in series
Four 200 ohms at 2 watts in parallel = 50 ohms at 8 watts. Two 25 ohms at 2 watts in series = 50 ohms at 4 watts. Ten 500 ohms at 0.25 watts in parallel = 50 ohms at 2.5 watts. Two 100 ohms at 5 watts in series = 200 ohms at 10 watts.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
How much current is drawn by a 12-volt, 30-watt light bulb?
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0.4 amperes
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Correct Answer2.5 amperes
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4.8 amperes
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18 amperes
The Power Law: P = E * I, power is voltage times current. Transformed to solve for I, it becomes I = P / E. In this example, I = 30 watts / 12 volts.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
What is the power consumption of two 10-ohm resistors connected in series with a 10-volt battery?
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20 watts
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Correct Answer5 watts
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2 watts
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0.5 watts
Two 10-ohm resistors in series present a total resistance of 20 ohms. Use Ohm's Law ( I = E / R ) to compute current as 10 volts divided by 20 ohms = 0.5 amperes. The Power Law: P = E * I, power is voltage times current. Power, for this example, becomes 10 volts times 0.5 amperes = 5 watts.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
What is the advantage of replacing a 50-ohm resistor with a parallel combination of two 100-ohm resistors of the same power rating?
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Same resistance but lesser power rating
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Lesser resistance and same power rating
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Greater resistance and same power rating
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Correct AnswerSame resistance but greater power rating
This is about POWER RATING, not resistance. Two identical resistors can safely dissipate TWICE as much power as only one. Two resistors of 100 ohms in PARALLEL yield a total resistance of 50 ohms ( In a parallel circuit with IDENTICAL resistors, total resistance is value divided by number ).
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
Resistor wattage ratings are:
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Correct Answerdetermined by heat dissipation qualities
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variable in steps of one hundred
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calculated according to physical size and tolerance rating
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expressed in joules
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