Ohm's Law / Power
Basic Qualification Question Bank for Amateur Radio Operator Certificate Examinations 12 June, 2014

Ohm's Law / Power


B-005-002-009 Voltage drop means:
A the difference in voltage at output terminals of a transformer
B the voltage which is dissipated before useful work is accomplished
C the voltage developed across the terminals of a component
D any point in a radio circuit which has zero voltage

B-005-003-004 Which electrical circuit will have no current?
A A short circuit
B A complete circuit
C A closed circuit
D An open circuit

B-005-003-005 Which electrical circuit draws too much current?
A A dead circuit
B A closed circuit
C An open circuit
D A short circuit

B-005-004-001 If a current of 2 amperes flows through a 50-ohm resistor, what is the voltage across the resistor?
A 100 volts
B 48 volts
C 52 volts
D 25 volts

B-005-004-002 How is the current in a DC circuit calculated when the voltage and resistance are known?
A Current equals voltage divided by resistance
B Current equals resistance multiplied by voltage
C Current equals resistance divided by voltage
D Current equals power divided by voltage

B-005-004-003 How is the resistance in a DC circuit calculated when the voltage and current are known?
A Resistance equals current divided by voltage
B Resistance equals voltage divided by current
C Resistance equals current multiplied by voltage
D Resistance equals power divided by voltage

B-005-004-004 How is the voltage in a DC circuit calculated when the current and resistance are known?
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-005-004-005 If a 12-volt battery supplies 0.25 ampere to a circuit, what is the circuit's resistance?
A 0.25 ohm
B 48 ohms
C 3 ohms
D 12 ohms

B-005-004-006 Calculate the value of resistance necessary to drop 100 volts with current flow of 0.8 milliamperes:
A 1250 ohms
B 1.25 kilohms
C 125 kilohms
D 125 ohms

B-005-004-007 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
C 220 volts
D 2220 volts

B-005-004-008 A lamp has a resistance of 30 ohms and a 6 volt battery is connected. The current flow will be:
A 0.5 ampere
B 0.005 ampere
C 0.2 ampere
D 2 amperes

B-005-004-009 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 225 volts
B 5 volts
C 8 volts
D 175 volts

B-005-004-010 The resistance of a circuit can be found by using one of the following:
A R = E x I
B R = E/I
C R = I/E
D R = E/R

B-005-004-011 If a 3 volt battery supplies 300 milliamperes to a circuit, the circuit resistance is:
A 5 ohms
B 3 ohms
C 10 ohms
D 9 ohms

B-005-005-001 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
D It equals the sum of the branch current through each resistor


B-005-005-002 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
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-005-005-003 Total resistance in a parallel circuit:
A depends upon the applied voltage
B is always less than the smallest resistance
C depends upon the voltage drop across each branch
D could be equal to the resistance of one branch

B-005-005-004 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 80 milliamperes
B 40 milliamperes
C 80 amperes
D 40 amperes

B-005-005-005 The total resistance of resistors connected in series is:
A equal to the lowest resistance present
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-005-005-006 Five 10 ohm resistors connected in series equals:
A 5 ohms
B 10 ohms
C 1 ohm
D 50 ohms

(B) Which series combination of resistors would replace a single 120 ohm resistor?
A Five 100 ohm
B Five 24 ohm
C Six 22 ohm
D Two 62 ohm

B-005-005-008 If ten resistors of equal value were wired in parallel, the total resistance would be:
A 10 + R
B R / 10
C 10 / R
D 10 x R

B-005-005-009 The total resistance of four 68 ohm resistors wired in parallel is:
A 272 ohms
B 17 ohms
C 12 ohms
D 34 ohms

B-005-005-010 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
C A has half the resistance of B
D the voltage across B is twice that across A

B-005-005-011 The total current in a parallel circuit is equal to the:
A current in any one of the parallel branches
B sum of the currents through all the parallel branches
C source voltage divided by the value of one of the resistive elements
D source voltage divided by the sum of the resistive elements


B-005-006-001 Why would a large size resistor be used instead of a smaller one of the same resistance?
A For less impedance in the circuit
B For greater power dissipation
C For better response time
D For a higher current gain

B-005-006-002 How many watts of electrical power are used by a 12 volt DC light bulb that draws 0.2 ampere?
A 6 watts
B 2.4 watts
C 60 watts
D 24 watts

B-005-006-003 The DC input power of a transmitter operating at 12 volts and drawing 500 milliamperes would be:
A 6 watts
B 20 watts
C 500 watts
D 12 watts

B-005-006-004 When two 500 ohm 1 watt resistors are connected in series, the maximum total power that can be dissipated by the resistors is:
A 2 watts
B 1 watt
C 1/2 watt
D 4 watts

B-005-006-005 When two 500 ohm 1 watt resistors are connected in parallel, they can dissipate a maximum total power of:
A 1/2 watt
B 1 watt
C 4 watts
D 2 watts

(A) If the voltage applied to two resistors in series is doubled, how much will the total power change?
A Increase four times
B Decrease to half
C Double
D No change

B-005-006-007 Which combination of resistors could make up a 50 ohms dummy load capable of safely dissipating 5 watts?
A Two 5-watt 100 ohms resistors in series
B Two 2-watt 25 ohms resistors in series
C Ten quarter-watt 500 ohms resistors in parallel
D Four 2-watt 200 ohms resistors in parallel

B-005-006-008 A 12 volt light bulb is rated at a power of 30 watts. The current drawn would be:
A 30/12 amperes
B 18 amperes
C 360 amperes
D 12/30 amperes

B-005-006-009 If two 10 ohm resistors are connected in series with a 10 volt battery, the power consumption would be:
A 5 watts
B 10 watts
C 20 watts
D 100 watts

B-005-006-010 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 greater resistance and similar power rating
B lesser resistance and similar power rating
C the same resistance but greater power rating
D the same resistance but lesser power rating

B-005-006-011 Resistor wattage ratings are:
A calculated according to physical size and tolerance rating
B expressed in joules
C variable in steps of one hundred
D determined by heat dissipation qualities



B-005-003-001 What is the word used to describe the rate at which electrical energy is used?
A Resistance
B Power
C Current
D Voltage

B-005-003-002 If you have light bulbs marked 40 watts, 60 watts and 100 watts, which one will use electrical energy the fastest?
A The 40 watt bulb
B The 60 watt bulb
C The 100 watt bulb
D They will all be the same

B-005-003-003 What is the basic unit of electrical power?
A The watt
B The ampere
C The volt
D The ohm

B-005-003-006 Power is expressed in:
A watts
B volts
C amperes
D ohms

B-005-003-007 Which of the following two quantities should be multiplied together to find power?
A Voltage and current
B Inductance and capacitance
C Voltage and inductance
D Resistance and capacitance

B-005-003-008 Which two electrical units multiplied together give the unit "watts"?
A Volts and amperes
B Volts and farads
C Farads and henrys
D Amperes and henrys

B-005-003-009 A resistor in a circuit becomes very hot and starts to burn. This is because the resistor is dissipating too much:
A power
B voltage
C resistance
D current

High power resistors are usually large with heavy leads. The size aids the operation of the resistor by:
A making it shock proof
B allowing heat to dissipate more readily
C allowing higher voltage to be handled
D increasing the effective resistance of the resistor

B-005-003-011 The resistor that could dissipate the most heat would be marked:
A 100 ohms
B 2 ohms
C 0.5 watt
D 20 watts
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November 20, 2017