Ohm's Law and Power.
Subel. L03a
43 questions
L03a
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Subelement L03a
Section L03a
If you have a hand-held transceiver which puts out 500 milliwatts, how many watts would this be?
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50
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0.02
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Correct Answer0.5
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5
A thousand milliwatts is one watt. Converting from milliwatts to watts: from small units to larger units, requires fewer digits, decimal point moves to the left by three positions, a thousand times less.
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 word used to describe the rate at which electrical energy is used?
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Resistance
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Correct AnswerPower
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Current
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Voltage
If you have light bulbs marked 40 watts, 60 watts and 100 watts, which one will use electrical energy the fastest?
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Correct AnswerThe 100 watt bulb
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They will all be the same
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The 40 watt bulb
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The 60 watt bulb
How fast does each one make the electrical utility meter on the side of your house spin ? The device with the highest wattage spins it the fastest.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Power, expressed in watts = voltage, in volts, TIMES current, in amperes. P = E * I. Watts = volts * amperes. The watt describe how fast electrical energy is used.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
Power, expressed in watts = voltage, in volts, TIMES current, in amperes. P = E * I. Watts = volts * amperes. The watt describe how fast electrical energy is used.
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 the following two quantities should be multiplied together to find power?
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Voltage and inductance
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Resistance and capacitance
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Correct AnswerVoltage and current
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Inductance and capacitance
Power, expressed in watts = voltage, in volts, TIMES current, in amperes. P = E * I. Watts = volts * amperes. The watt describe how fast electrical energy is used.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
Which two electrical units multiplied together give the unit "watts"?
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Volts and farads
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Farads and henrys
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Amperes and henrys
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Correct AnswerVolts and amperes
Power, expressed in watts = voltage, in volts, TIMES current, in amperes. P = E * I. Watts = volts * amperes. The watt describe how fast electrical energy is used.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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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:
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voltage
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resistance
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current
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Correct Answerpower
Power is voltage times current, P = E * I. When current flows through a resistor, a 'voltage drop' ensues. Volts times amperes become watts. Power is dissipated as heat.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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High power resistors are usually large with heavy leads. The size aids the operation of the resistor by:
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making it shock proof
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Correct Answerallowing heat to dissipate more readily
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allowing higher voltage to be handled
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increasing the effective resistance of the resistor
The resistor that could dissipate the most heat would be marked:
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2 ohms
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0.5 watt
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Correct Answer20 watts
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100 ohms
If a current of 2 amperes flows through a 50-ohm resistor, what is the voltage across the resistor?
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25 volts
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Correct Answer100 volts
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48 volts
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52 volts
Ohm's Law ( I = E / R ) becomes E = R*I when solving for E. Voltage = resistance times current. Volts = ohms * amperes. 50 ohms * 2 amperes = 100 volts.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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How is the current in a DC circuit calculated when the voltage and resistance are known?
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Current equals resistance multiplied by voltage
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Current equals resistance divided by voltage
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Current equals power divided by voltage
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Correct AnswerCurrent equals voltage divided by resistance
How is the resistance in a DC circuit calculated when the voltage and current are known?
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Resistance equals current divided by voltage
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Correct AnswerResistance equals voltage divided by current
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Resistance equals current multiplied by voltage
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Resistance equals power divided by voltage
How is the voltage in a DC circuit calculated when the current and resistance are known?
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Correct AnswerVoltage equals current multiplied by resistance
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Voltage equals current divided by resistance
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Voltage equals resistance divided by current
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Voltage equals power divided by current
If a 12-volt battery supplies 0.25 ampere to a circuit, what is the circuit's resistance?
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3 ohms
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12 ohms
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0.25 ohm
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Correct Answer48 ohms
Ohm's Law ( I = E / R ) becomes R = E / I when solving for R. Resistance is voltage divided by current. Ohms = volts / amperes. 12 volts / 0.25 amperes = 48 ohms.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Calculate the value of resistance necessary to drop 100 volts with current flow of 0.8 milliamperes:
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1250 ohms
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1.25 kilohms
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Correct Answer125 kilohms
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125 ohms
Ohm's Law ( I = E / R ) becomes R = E / I when solving for R. Resistance is voltage divided by current. Ohms = volts / amperes. 100 volts / 0.0008 amperes = 125 000 ohms = 125 kilohms. [ Note that volts divided by milliamperes is kilohm ]
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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The voltage required to force a current of 4.4 amperes through a resistance of 50 ohms is:
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22.0 volts
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0.220 volt
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Correct Answer220 volts
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2220 volts
Ohm's Law ( I = E / R ) becomes E = R*I when solving for E. Voltage is resistance times current. Volts = ohms * amperes. 50 ohms * 4.4 amperes = 220 volts.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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A lamp has a resistance of 30 ohms and a 6 volt battery is connected. The current flow will be:
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2 amperes
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0.5 ampere
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0.005 ampere
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Correct Answer0.2 ampere
What voltage would be needed to supply a current of 200 milliamperes, to operate an electric lamp which has a resistance of 25 ohms?
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175 volts
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225 volts
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Correct Answer5 volts
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8 volts
Ohm's Law ( I = E / R ) becomes E = R*I when solving for E. Voltage is resistance times current. Volts = ohms * amperes. 25 ohms * 0.200 amperes = 5 volts.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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The resistance of a circuit can be found by using one of the following:
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R = I/E
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R = E/R
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R = E x I
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Correct AnswerR = E/I
If a 3 volt battery supplies 300 milliamperes to a circuit, the circuit resistance is:
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9 ohms
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5 ohms
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3 ohms
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Correct Answer10 ohms
Ohm's Law ( I = E / R ) becomes R = E / I when solving for R. Resistance is voltage divided by current. Ohms = volts / amperes. 3 volts / 0.300 amperes = 10 ohms.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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In a parallel circuit with a voltage source and several branch resistors, how is the total current related to the current in the branch resistors?
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It equals the average of the branch current through each resistor
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It decreases as more parallel resistors are added to the circuit
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It is the sum of each resistor's voltage drop multiplied by the total number of resistors
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Correct AnswerIt equals the sum of the branch current through each resistor
Each resistor added in parallel to the source draws some current ( in accordance with Ohm's Law, I = E / R ). The total current that the source must supply becomes the SUM of all these individual currents. Just like in your house, the total current drawn from the utility company is the sum of all the devices turned-on.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Three resistors, respectively rated at 10, 15 and 20 ohms are connected in parallel across a 6-volt battery. Which statement is true?
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The voltage drop across each resistance added together equals 6 volts
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The voltage drop across the 20 ohm resistance is greater than the voltage across the 10 ohm resistance
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Correct AnswerThe current through the 10 ohms, 15 ohms and 20 ohms separate resistances, when added together, equals the total current drawn from the battery
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The current flowing through the 10 ohm resistance is less than that flowing through the 20 ohm resistance
key word: PARALLEL. In a parallel circuit, the total current is the sum of the currents. All resistors are subjected to the same voltage in a PARALLEL circuit. Ohm's Law tells us that the smaller resistor will draw more current than the others.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Total resistance in a parallel circuit:
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depends upon the voltage drop across each branch
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could be equal to the resistance of one branch
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depends upon the applied voltage
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Correct Answeris always less than the smallest resistance
key word: PARALLEL. In a parallel circuit, each added resistor adds to the current drawn from the source. If more and more current is drawn, the total resistance must be going down. In PARALLEL, the total resistance is less than the smallest.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Two resistors are connected in parallel and are connected across a 40 volt battery. If each resistor is 1000 ohms, the total current is:
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40 milliamperes
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80 amperes
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40 amperes
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Correct Answer80 milliamperes
Ohm's Law ( I = E / R ). Each resistor draws this much current: 40 volts divided by 1000 ohms = 0.040 amperes = 40 milliamperes. In PARALLEL, total current is the sum of the currents. Method B: identical resistors in parallel, total resistance is value divided by number. In this case, 1000 / 2 = 500 ohms. 40 volts / 500 ohms = 0.08 amperes = 80 milliamperes.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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The total resistance of resistors connected in series is:
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equal to the lowest resistance present
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Correct Answergreater than the resistance of any one resistor
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less than the resistance of any one resistor
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equal to the highest resistance present
key word: SERIES. In a series circuit, there is only one current. This current must wrestle with each resistor one after the other. In SERIES, total resistance is the sum of the resistances. The same current flows through all of them.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Which series combination of resistors would replace a single 120 ohm resistor?
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Six 22 ohm
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Two 62 ohm
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Five 100 ohm
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Correct AnswerFive 24 ohm
If ten resistors of equal value were wired in parallel, the total resistance would be:
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10 + R
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Correct AnswerR / 10
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10 / R
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10 x R
key word: PARALLEL. In a parallel circuit with IDENTICAL resistors, total resistance is value divided by number. In this example, the value of one R divided by 10.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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The total resistance of four 68 ohm resistors wired in parallel is:
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Correct Answer17 ohms
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12 ohms
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34 ohms
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272 ohms
key word: PARALLEL. In a parallel circuit with IDENTICAL resistors, total resistance is value divided by number. In this example, 68 / 4 yields 17.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Two resistors are in parallel. Resistor A carries twice the current of resistor B, which means that:
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the voltage across A is twice that across B
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B has half the resistance of A
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Correct AnswerA has half the resistance of B
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the voltage across B is twice that across A
key word: PARALLEL. All resistors in a parallel circuit are subjected to the same voltage. Per Ohm's Law ( I = E / R, current = voltage divided by resistance ), if resistor A draws twice the current of resistor B, it must have half the resistance of Resistor B.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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The total current in a parallel circuit is equal to the:
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source voltage divided by the sum of the resistive elements
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current in any one of the parallel branches
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Correct Answersum of the currents through all the parallel branches
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source voltage divided by the value of one of the resistive elements
key word: PARALLEL. In a parallel circuit, the total current is the sum of the currents. Each branch is subjected to the same voltage and draws a current in accordance with Ohm's Law ( I = E / R, current = voltage divided by resistance ).
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Why would a large size resistor be used instead of a smaller one of the same resistance?
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For a higher current gain
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For less impedance in the circuit
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Correct AnswerFor greater power dissipation
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For better response time
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.
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How many watts of electrical power are used by a 12 volt DC light bulb that draws 0.2 ampere?
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60 watts
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24 watts
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6 watts
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Correct Answer2.4 watts
P = E * I, power is voltage times current, watts = volts * amperes. 12 volts * 0.2 amperes = 2.4 watts [ VDC = 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.
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The DC input power of a transmitter operating at 12 volts and drawing 500 milliamperes would be:
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12 watts
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Correct Answer6 watts
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20 watts
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500 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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1 watt
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1/2 watt
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4 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.
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When two 500 ohm 1 watt resistors are connected in parallel, they can dissipate a maximum total power of:
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1 watt
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4 watts
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Correct Answer2 watts
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1/2 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.
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If the voltage applied to two resistors in series is doubled, how much will the total power change?
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Correct AnswerIncrease four times
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Decrease to half
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Double
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No change
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.
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Which combination of resistors could make up a 50 ohms dummy load capable of safely dissipating 5 watts?
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Correct AnswerFour 2-watt 200 ohms resistors in parallel
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Two 5-watt 100 ohms resistors in series
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Two 2-watt 25 ohms resistors in series
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Ten quarter-watt 500 ohms resistors in parallel
Four 200 ohms @ 2 watts in parallel = 50 ohms @ 8 watts. Two 25 ohms @ 2 watts in series = 50 ohms @ 4 watts. Ten 500 ohms @ 0.25 watts in parallel = 50 ohms @ 2.5 watts. Two 100 ohms @ 5 watts in series = 200 ohms @ 10 watts.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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A 12 volt light bulb is rated at a power of 30 watts. The current drawn would be:
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12/30 amperes
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Correct Answer30/12 amperes
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18 amperes
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360 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
If two 10 ohm resistors are connected in series with a 10 volt battery, the power consumption would be:
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100 watts
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Correct Answer5 watts
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10 watts
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20 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.
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One advantage of replacing a 50 ohm resistor with a parallel combination of two similarly rated 100 ohm resistors is that the parallel combination will have:
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lesser resistance and similar power rating
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Correct Answerthe same resistance but greater power rating
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the same resistance but lesser power rating
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greater resistance and similar 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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variable in steps of one hundred
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Correct Answerdetermined by heat dissipation qualities
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calculated according to physical size and tolerance rating
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expressed in joules
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