Canadian (from VE2AAY) Basic Qualification pool, section L03a

Subelement L03a

Ohm's Law and Power.

Section L03a

B-5-1-5

If you have a hand-held transceiver which puts out 500 milliwatts, how many watts would this be?

A.
50
B.
0.02
Correct Answer
C.
0.5
D.
5

B-5-1-5

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.

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B-5-3-1

What is the word used to describe the rate at which electrical energy is used?

A.
Resistance
Correct Answer
B.
Power
C.
Current
D.
Voltage

B-5-3-1

The watt is the unit used to measure the rate of energy use.

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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B-5-3-2

If you have light bulbs marked 40 watts, 60 watts and 100 watts, which one will use electrical energy the fastest?

Correct Answer
A.
The 100 watt bulb
B.
They will all be the same
C.
The 40 watt bulb
D.
The 60 watt bulb

B-5-3-2

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.

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B-5-3-3

What is the basic unit of electrical power?

A.
The ampere
B.
The volt
C.
The ohm
Correct Answer
D.
The watt

B-5-3-3

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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B-5-3-6

Power is expressed in:

A.
volts
B.
amperes
C.
ohms
Correct Answer
D.
watts

B-5-3-6

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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B-5-3-7

Which of the following two quantities should be multiplied together to find power?

A.
Voltage and inductance
B.
Resistance and capacitance
Correct Answer
C.
Voltage and current
D.
Inductance and capacitance

B-5-3-7

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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B-5-3-8

Which two electrical units multiplied together give the unit "watts"?

A.
Volts and farads
B.
Farads and henrys
C.
Amperes and henrys
Correct Answer
D.
Volts and amperes

B-5-3-8

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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B-5-3-9

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

A.
voltage
B.
resistance
C.
current
Correct Answer
D.
power

B-5-3-9

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.

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B-5-3-10

High power resistors are usually large with heavy leads. The size aids the operation of the resistor by:

A.
making it shock proof
Correct Answer
B.
allowing heat to dissipate more readily
C.
allowing higher voltage to be handled
D.
increasing the effective resistance of the resistor

B-5-3-10

Resistors are rated for resistance in ohms and safe power dissipation in watts.

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B-5-3-11

The resistor that could dissipate the most heat would be marked:

A.
2 ohms
B.
0.5 watt
Correct Answer
C.
20 watts
D.
100 ohms

B-5-3-11

Resistors are rated for resistance in ohms and safe power dissipation in 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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B-5-4-1

If a current of 2 amperes flows through a 50-ohm resistor, what is the voltage across the resistor?

A.
25 volts
Correct Answer
B.
100 volts
C.
48 volts
D.
52 volts

B-5-4-1

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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B-5-4-2

How is the current in a DC circuit calculated when the voltage and resistance are known?

A.
Current equals resistance multiplied by voltage
B.
Current equals resistance divided by voltage
C.
Current equals power divided by voltage
Correct Answer
D.
Current equals voltage divided by resistance

B-5-4-2

Ohm's Law is I = E / R, current is voltage divided by resistance. Amperes = volts / 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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B-5-4-3

How is the resistance in a DC circuit calculated when the voltage and current are known?

A.
Resistance equals current divided by voltage
Correct Answer
B.
Resistance equals voltage divided by current
C.
Resistance equals current multiplied by voltage
D.
Resistance equals power divided by voltage

B-5-4-3

Ohm's Law ( I = E / R ) becomes R = E / I when solving for R. Resistance is voltage divided by current. Ohms = volts / amperes.

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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B-5-4-4

How is the voltage in a DC circuit calculated when the current and resistance are known?

Correct Answer
A.
Voltage equals current multiplied by resistance
B.
Voltage equals current divided by resistance
C.
Voltage equals resistance divided by current
D.
Voltage equals power divided by current

B-5-4-4

Ohm's Law ( I = E / R ) becomes E = R*I when solving for E. Voltage is resistance times current. Volts = ohms * amperes.

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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B-5-4-5

If a 12-volt battery supplies 0.25 ampere to a circuit, what is the circuit's resistance?

A.
3 ohms
B.
12 ohms
C.
0.25 ohm
Correct Answer
D.
48 ohms

B-5-4-5

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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B-5-4-6

Calculate the value of resistance necessary to drop 100 volts with current flow of 0.8 milliamperes:

A.
1250 ohms
B.
1.25 kilohms
Correct Answer
C.
125 kilohms
D.
125 ohms

B-5-4-6

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 ]

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B-5-4-7

The voltage required to force a current of 4.4 amperes through a resistance of 50 ohms is:

A.
22.0 volts
B.
0.220 volt
Correct Answer
C.
220 volts
D.
2220 volts

B-5-4-7

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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B-5-4-8

A lamp has a resistance of 30 ohms and a 6 volt battery is connected. The current flow will be:

A.
2 amperes
B.
0.5 ampere
C.
0.005 ampere
Correct Answer
D.
0.2 ampere

B-5-4-8

Ohm's Law ( I = E / R ). Current is voltage divided by resistance. Amperes = volts / ohms. 6 volts / 30 ohms = 0.2 amperes.

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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B-5-4-9

What voltage would be needed to supply a current of 200 milliamperes, to operate an electric lamp which has a resistance of 25 ohms?

A.
175 volts
B.
225 volts
Correct Answer
C.
5 volts
D.
8 volts

B-5-4-9

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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B-5-4-10

The resistance of a circuit can be found by using one of the following:

A.
R = I/E
B.
R = E/R
C.
R = E x I
Correct Answer
D.
R = E/I

B-5-4-10

Ohm's Law ( I = E / R ) becomes R = E / I when solving for R. Resistance is voltage divided by current. Ohms = volts / amperes.

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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B-5-4-11

If a 3 volt battery supplies 300 milliamperes to a circuit, the circuit resistance is:

A.
9 ohms
B.
5 ohms
C.
3 ohms
Correct Answer
D.
10 ohms

B-5-4-11

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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B-5-5-1

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?

A.
It equals the average of the branch current through each resistor
B.
It decreases as more parallel resistors are added to the circuit
C.
It is the sum of each resistor's voltage drop multiplied by the total number of resistors
Correct Answer
D.
It equals the sum of the branch current through each resistor

B-5-5-1

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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B-5-5-2

Three resistors, respectively rated at 10, 15 and 20 ohms are connected in parallel across a 6-volt battery. Which statement is true?

A.
The voltage drop across each resistance added together equals 6 volts
B.
The voltage drop across the 20 ohm resistance is greater than the voltage across the 10 ohm resistance
Correct Answer
C.
The current through the 10 ohms, 15 ohms and 20 ohms separate resistances, when added together, equals the total current drawn from the battery
D.
The current flowing through the 10 ohm resistance is less than that flowing through the 20 ohm resistance

B-5-5-2

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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B-5-5-3

Total resistance in a parallel circuit:

A.
depends upon the voltage drop across each branch
B.
could be equal to the resistance of one branch
C.
depends upon the applied voltage
Correct Answer
D.
is always less than the smallest resistance

B-5-5-3

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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B-5-5-4

Two resistors are connected in parallel and are connected across a 40 volt battery. If each resistor is 1000 ohms, the total current is:

A.
40 milliamperes
B.
80 amperes
C.
40 amperes
Correct Answer
D.
80 milliamperes

B-5-5-4

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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B-5-5-5

The total resistance of resistors connected in series is:

A.
equal to the lowest resistance present
Correct Answer
B.
greater than the resistance of any one resistor
C.
less than the resistance of any one resistor
D.
equal to the highest resistance present

B-5-5-5

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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B-5-5-6

Five 10 ohm resistors connected in series equals:

A.
5 ohms
B.
10 ohms
C.
1 ohm
Correct Answer
D.
50 ohms

B-5-5-6

key word: SERIES. In SERIES, total resistance is the sum of the resistances.

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B-5-5-7

Which series combination of resistors would replace a single 120 ohm resistor?

A.
Six 22 ohm
B.
Two 62 ohm
C.
Five 100 ohm
Correct Answer
D.
Five 24 ohm

B-5-5-7

key word: SERIES. In SERIES, total resistance is the sum of the resistances. Five times twenty-four = 120.

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B-5-5-8

If ten resistors of equal value were wired in parallel, the total resistance would be:

A.
10 + R
Correct Answer
B.
R / 10
C.
10 / R
D.
10 x R

B-5-5-8

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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B-5-5-9

The total resistance of four 68 ohm resistors wired in parallel is:

Correct Answer
A.
17 ohms
B.
12 ohms
C.
34 ohms
D.
272 ohms

B-5-5-9

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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B-5-5-10

Two resistors are in parallel. Resistor A carries twice the current of resistor B, which means that:

A.
the voltage across A is twice that across B
B.
B has half the resistance of A
Correct Answer
C.
A has half the resistance of B
D.
the voltage across B is twice that across A

B-5-5-10

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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B-5-5-11

The total current in a parallel circuit is equal to the:

A.
source voltage divided by the sum of the resistive elements
B.
current in any one of the parallel branches
Correct Answer
C.
sum of the currents through all the parallel branches
D.
source voltage divided by the value of one of the resistive elements

B-5-5-11

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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B-5-6-1

Why would a large size resistor be used instead of a smaller one of the same resistance?

A.
For a higher current gain
B.
For less impedance in the circuit
Correct Answer
C.
For greater power dissipation
D.
For better response time

B-5-6-1

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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B-5-6-2

How many watts of electrical power are used by a 12 volt DC light bulb that draws 0.2 ampere?

A.
60 watts
B.
24 watts
C.
6 watts
Correct Answer
D.
2.4 watts

B-5-6-2

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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B-5-6-3

The DC input power of a transmitter operating at 12 volts and drawing 500 milliamperes would be:

A.
12 watts
Correct Answer
B.
6 watts
C.
20 watts
D.
500 watts

B-5-6-3

P = E * I, power is voltage times current, watts = volts * amperes. 12 volts * 0.5 amperes = 6 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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B-5-6-4

When two 500 ohm 1 watt resistors are connected in series, the maximum total power that can be dissipated by the resistors is:

A.
1 watt
B.
1/2 watt
C.
4 watts
Correct Answer
D.
2 watts

B-5-6-4

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 ]

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B-5-6-5

When two 500 ohm 1 watt resistors are connected in parallel, they can dissipate a maximum total power of:

A.
1 watt
B.
4 watts
Correct Answer
C.
2 watts
D.
1/2 watt

B-5-6-5

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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B-5-6-6

If the voltage applied to two resistors in series is doubled, how much will the total power change?

Correct Answer
A.
Increase four times
B.
Decrease to half
C.
Double
D.
No change

B-5-6-6

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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B-5-6-7

Which combination of resistors could make up a 50 ohms dummy load capable of safely dissipating 5 watts?

Correct Answer
A.
Four 2-watt 200 ohms resistors in parallel
B.
Two 5-watt 100 ohms resistors in series
C.
Two 2-watt 25 ohms resistors in series
D.
Ten quarter-watt 500 ohms resistors in parallel

B-5-6-7

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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B-5-6-8

A 12 volt light bulb is rated at a power of 30 watts. The current drawn would be:

A.
12/30 amperes
Correct Answer
B.
30/12 amperes
C.
18 amperes
D.
360 amperes

B-5-6-8

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.

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B-5-6-9

If two 10 ohm resistors are connected in series with a 10 volt battery, the power consumption would be:

A.
100 watts
Correct Answer
B.
5 watts
C.
10 watts
D.
20 watts

B-5-6-9

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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B-5-6-10

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:

A.
lesser resistance and similar power rating
Correct Answer
B.
the same resistance but greater power rating
C.
the same resistance but lesser power rating
D.
greater resistance and similar power rating

B-5-6-10

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.

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B-5-6-11

Resistor wattage ratings are:

A.
variable in steps of one hundred
Correct Answer
B.
determined by heat dissipation qualities
C.
calculated according to physical size and tolerance rating
D.
expressed in joules

B-5-6-11

Materials, shape, construction all interact to determine heat dissipation capabilities. Tolerance is a misleading clue.

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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