Electrical Theory, Quarter Two Review
8.11 Kilo What is the kW of a 75W load?
0.075 kW 75 divided by 1000 = 0.075
9.7 Ohm's Law Formula Circle What is the resistance of the circuit conductors when the conductor voltage drop is 7.20V and the current flow is 50A? Formula: R =E/I
0.14 7.20/50 = 0.144 or 0.14
8.3 Fractions The approximate decimal equivalent for the fraction 4/18 is?
0.20 4 divided by 18 = 0.22
8.3 Fractions The decimal equivalent for the fraction 1/2 is?
0.50 1 divided by 2 = 0.5
8.4 Percentages The decimal equivalent for 75% is?
0.75 Drop the % sign and move the decimal point over two places to the left. 75% = 0.75
8.7 Reciprocals What is the reciprocal of 1.25?
0.80 To obtain the reciprocal of a number, convert the number into a fraction with the number one as the numerator (top number). 1 divided by 1.25 = 0.80
8.9 Square Root The square root of 3 is?
1.732
8.13 Parentheses What is the maximum distance that two 14 AWG conductors can be run if they carry 16A and the maximum allowable voltage drop is 10V? Formula: D = (Cmil x VD) / (2 x K x I) D = (4,110 cmil x 10V) / (2 x 12.90 ohms x 16A)
100 ft (4,110 x 10) / (2 x 12.9 x 16) (41,100) / (412.8) 99.56 or 100 ft
9.11 Power Losses of Conductors The total circuit resistance of two 12 AWG conductors (each 100 ft long) is 0.40 ohms. If the current of the circuit is 16A, what is the power loss of both conductors? Formula:P = (I x I) x E
100W (16 x 16) x 0.4 = P (256) x 0.4 = 102.4 or 100W
8.14 Testing Your Answer For Reasonableness The output power of a transformer is 100W and the transformer efficiency is 90%. What is the transformer input if the output is lower than the input? Formula: Input = Output/Efficiency
110W 90% = 0.90 100 / 0.90 = Input 100 / 0.90 = 111.11
8.8 Squaring a Number The numeric equivalent of 12 squared is ____.
144 12 x 12 = 144
8.8 Squaring a Number The numeric equivalent of 4 squared is ____.
16 4 x 4 = 16
9.8 Pie Formula Circle What is the power loss in watts of a conductor that carries 24A and has a drop of 7.20V? Formula: P = I x E
175W 24 x 7.20 = 172.8 or 175
8.4 Percentages The decimal equivalent for 225% is?
2.25 Drop the % sign and move the decimal point over two places to the left. 225% = 2.25
9.13 Power Changes with the Square of the Voltage What is the power consumed by a 10 kW heat strip that's rated 230V, if it's connected to a 115V circuit? Formula: P = (E x E) / R
2.50 kW (230 x230) x 10 kW = resistance (52,900) x 10,000 = 5.29 (115 x115) x 5.29 = power consumed (13,225) x 5.29 = 2,500W or 2.50 kW
8.5 Multiplier An overcurrent protection device (circuit breaker or fuse) must be sized no less than 125% of the continuous load. If the load is 16A, the overcurrent protection device will have to be sized no less than____.
20A 125% = 1.25 16 x 1.25 = 20 The breaker must be no smaller than 20A
8.10 Volume What is the volume (in cubic inches) of a 4 x 4 x 1.50 in. box?
24 cu in. 4 x 4 = 16 16 x 1.50 = 24
8.12 Rounding Off The approximate sum of 2, 7, 8 and 9 is equal to ____.
25 2 + 7 + 8 + 9 = 26
8.4 Percentages The decimal equivalent for 300% is?
3 Drop the % sign and move the decimal point two places to the left. 300% = 3.00
8.9 Square Root What is the approximate square root of 1000?
32
9.11 Power Losses What is the conductor power loss for a 120V circuit that has a 3 percent voltage drop and carries a current flow of 12A? Formula: P = I x E
43W 120 x 3% = voltage drop 120 x 0.03 = 3.6V 12 x 3.6 = 43.2 or 43W
8.13 Parentheses What is the current in amperes of an 18 kW, 208V, three-phase load? Use the equation: Current: I = 18,000W / (208V x 1.732)
50A 18,000W / (208V x 1.732) = I 18,000W / (360) = I 18,000W / 360 = 50
8.8 Squaring a Number What is the power consumed in watts by a 12 AWG conductor that is 100 ft long and has a resistance (R) of 0.20 ohms, when the current (I) in the circuit's is 16A? Formula: Power = (I x I) x R.
50W 16 x 16 = 256 256 x 0.20 = 51.2
9.7 Ohm's Law Formula Circle What is the voltage drop of two 12 AWG conductors (total of .40 ohms for both conductors) supplying a 16A load, located 100 ft from the power supply? Formula: Evd = I x R
6.4 16 x 0.4 = 6.4
9.12 Cost of Power What does it cost per year ( at 8 cents per kWh ) for the power loss of a 12 AWG conductor ( 100 ft long ) that has a total resistance of 0.40 ohms and current flow of 16A? Formula: Cost per year = Power of the year in kWh x $0.08
72 (16 x 16) x 0.4 = Power loss (265) x 0.4 = 102.4W 102.4 = 0.1024 kWh 0.1024 x 24 = 2.4576 kW a day 2.4576 x 365 = 897.024 kW a year 897.024 x 0.08 = 71.76192 or $72 cost per year
9.9 Formula Wheel What is the approximate power consumed by a 10 kW heat strip rated 230V, when connected to 208V circuit? Formula: P = (E x E) / R
8.2 kW (230 x 230)V / 10,000W = (52,900)V / 10,000W = 5.29R (208 x 208)V / 5.29R = (43,264)V / 5.29R = 8178W or 8.178kW
8.7 Reciprocals A continuous load requires an overcurrent protection device sized no smaller than 125% of the load. What is the maximum continuous load permitted on a 100A overcurrent protection device?
80A 125% = 1.25 1 divided by 1.25 = 0.80 100 x 0.80 = 80
8.5 Multiplier The maximum continuous load on an overcurrent protection device is limited to 80% of the device rating. If the overcurrent device is rated 100A, the maximum continuous load is____.
80A 80% = 0.80 100 x 0.80 = 80 The maximum continuous load is 80A
8.6 Percent Increase The feeder calculated load for an 8 kW load, increased by 20% is ____.
9.60 kW 20% = 0.20 8 x 0.20 = 1.60 8 + 1.60 = 9.60 8 kW increased by 20% is 9.60 kW
8.10 Volume The volume of an enclosure is expressed in ____, and it is calculated by multiplying the length, by the width, by the depth of the enclosure.
Cubic Inches The volume of an enclosure is expressed in "cubic inches," and it is calculated by multiplying the length, by the width, by the depth of the enclosure.
9.5 Ohm's law The Ohm's law formula, I = E/R, states that current is ____ proportional to the voltage, and ____ proportional to the resistance.
Directly, Inversely The German physicist Georg Simon Ohm (1787 - 1845) stated that current is directionally proportional to voltage, and inversely proportional to resistance.
7.4 Voltage (Pressure) Electrical pressure is called "____," and it is measured in Volts.
EMF-Electromovtive Force or Potential Electrical pressure is called " EMF or Potential," and it is measured in volts.
6.4 Electromagnetic Relay "Normally Closed" means the contacts are closed when the coil is energized. True or False?
False "Normally Closed" means the contacts are "open" when the coil is energized. "Normally Closed" means that the contacts are closed when the relay is NOT energized, but open when the relay is energized. Contacts are sometimes referred to with a "form" designation as follows: Form B--Normally Closed or "B" Contact
9.2 Power Source The polarity and the output voltage from an ac power source never changes direction. True or False?
False Alternating current power sources produce voltage that changes polarity and magnitude.
8.9 Square Root Deriving the square root of a number is almost the same as squaring a number. True or False?
False Deriving th square root of a number is the opposite of squaring a number. The square root of 36 is a number that, when multiplied by itself, gives the product 36. The square root of 36 equals 6, because 6, multiplied by itself equals the number 36.
5.2 Field Intensity The field intensity around a conductor carrying current decreases with increased current flow, and is stronger the further the distance from the conductor. True or False?
False Field intensity (lines of flux) "increases" with increased current flow, but "weakens" as they get further from the conductor.
6.4 Electromagnetic Relay A holding relay is primarily used for worker convenience. True or False?
False Holding relays are used in many types of control Circuits, primarily for safety. One of the safety features of the holding relay is that once the relay is de-energized, the power to the equipment will be removed. In addition, the circuit cannot be re-energized unless the "start" button is pushed.
10.1 Practical Uses of the Series Circuit A 115/230V rated motor connected to a 230V circuit must have the windings connected in a series so that each winding receives at least 230V. True or False?
False It only needs 115V. If the motor had each winding receiving 230V it would be additive to 460V, because it's in series.
9.3 Conductance The best conductors, in order of their conductivity, are gold, silver, copper, and aluminum. True or False?
False The order is silver, copper, gold and aluminum.
9.2 Power Source The polarity and the output voltage from a DC power source changes direction. One terminal will be negative and the other will be positive. True or False?
False The polarity and the output voltage from a DC power source never changes direction.
9.13 Power Changes with the Square of the Voltage The voltage applied to a resistor dramatically affects the power consumed by that resistor because power is affected in direct proportion to the voltage. True or False?
False The voltage applied to a resistor dramatically affects the power consumed by that resistor. If the voltage is doubled, the power will increase by four times. If the voltage is decreased 50 percent, the power will decrease to 25 percent of its original value. Thus, for a small change in voltage, there is a considerable change in power consumption.
5.1 Electromagnetism in a Wire The direction of the electromagnetic fields around a conductor because of current flow is determined by the right-hand rule as it relates to electron theory. True or False?
False When current flows through a conductor, an electromagnetic fields develops around the wire. The direction of the electromagnetic field is determined by the left-hand rule as it relates to "Electron Current Flow Theory," or the right-hand rule as it relates to "Conventional Current Flow Theory."
5 Introduction When electrons are forced to move through a conductor, the magnetic fields of individual electrons subtract from one another. True or False?
False When electrons are forced to move (current flow) through a conductor, the magnetic fields of individual electrons "add" together.
9.2 Power Source The polarity and the output voltage from a dc power source changes direction. One terminal will be negative and the other will be positive. True or False
False dc power only flows in one direction
6.4 Electromagnetic Relay "Normally Open" means the the contacts are open when power is applied. True or False?
False "Normally Open" means the contacts are "closed" when power is applied. "Normally Open" means that the contacts are open (not touching each other) when power is NOT applied to the coil, but the contacts close when power is applied. Contacts are sometimes referred to with a "form" designation as follows: Form A--Normally Open or "A" Contact
9.2 Power Source The polarity and the output voltage from an ac power source will never change direction. True or False?
False Alternating Current or ac is a power sources produce a voltage that changes polarity and magnitude.
7.5 Resistance Aluminum has a lower resistance to the flow of electrons than does copper. True or False?
False An aluminum conductor has a greater resistance to the flow of electrons than an equivalent size copper.
7.5 Resistance Every component of an electrical circuit contains resistance, except the power supply. True or False?
False Every component in an electrical circuit (load and conductors) contains resistance, including the power supply (batteries, generators and transformers.)
9.6 Ohm's Law and Alternating Current In a dc circuit, the only opposition to current flow is the physical resistance of the material. This opposition is called "reactance" and is measured in ohms. True or False?
False In a dc circuit, the only opposition to current flow is the physical resistance of the material. This opposition is called "resistance" and is measured in ohms.
9.3 Conductance The best conductors, in order of their conductivity, are gold, silver, copper, and aluminum. True or False?
False silver, copper, gold, and aluminum
9.5 Ohm's Law Ohm's law demonstrates the relationship between circuit ____.
Intensity EMF Resistance Ohm's law demonstrates the relationship between a circuit's " current intensity (I), electromotive force (EMF or E), and resistance (R) in a dc circuit.
7.6 Electric current In electrical systems, the volume of electrons that move through a conductor is called the "circuit____."
Intensity In electrical systems, the volume of electrons that move through a conductor (amperes) is called the "intensity" of the current flow and is measured in amperes.
8.4 Percentages To change a percent value to a decimal or whole number, drop the percentage sign and move the decimal point two places to the ____.
Left To change a percent value to a decimal or whole number, drop the percentage sign and move the decimal point two places to the "left."
6.2 Electric Motors The electric motor works on the principle of the attracting and repelling forces of ____ fields.
Magnetic The electric motor works on the principle of attracting and repelling forces of "magnetic" fields.
6.1 Basic Electric Meters A clamp-on ac ammeter has a coil that is clamped around the conductor and detects the rising and falling ____ field being produced due to the ac flow through the conductor.
Magnetic A clamp-on ac ammeter has a coil that is clamped around the conductor and detects the rising and falling "Magnetic" field being produced due to the ac flow through the conductor.
8.5 Multiplier The method of increasing a number by another number is done by using a ____.
Mulitplier When a number needs to be changed by multiplying it by a percentage, this percentage is called a multiplier. The first step is to convert the percentage to a decimal, then multiply the original number by the decimal value.
9.1 Electrical Circuit According to the Electron Current Flow Theory, electrons leave the ____ terminal of the source, flow through the conductors and load(s), and return to the ____ terminal of the source.
Negative to Positive According to the Electron Current Flow Theory, electrons leave the "negative" terminal of the source, flow through the conductors and load(s), and return to the "positive" terminal of the source.
6.1 Basic Electric Meters Voltmeters are connected in ____ with the circuit and measure the difference of potential between the two test leads.
Parallel Voltmeters are connected in "parallel" with the circuit and measure the difference of potential between the two test leads.
7.7 Power "____" is defined as the rate of work measured by the unit called the watt.
Power Power is defined as the rate of work measured by the unit called the watt.
6.1 Basic Electric Meters Ohmmeters measure the ____ or opposition to current flow of a circuit or component.
Resistance Ohmmeters measure the "resistance" or opposition to current flow of a circuit or component.
6.1 Basic Electric Meters The Megger is used to measure very high ____ values, such as those found in cable insulation, or motor and transformer windings.
Resistance The Megger is used to measure very high-"resistance" values, such as those found in cable insulation, or motor and transformer windings.
6.1 Basic Electric Meters The Wheatstone bridge meter is used for extremely accurate ____ measurements.
Resistance The Wheatstone bridge meter is used for extremely accurate "resistance" measurements.
6.3 Electric Generators The ____ of a generator is forced to rotate while it is being subjected to the magnetic field of the stator.
Rotor The "rotor" of a generator is forced to rotate while it is being subjected to the magnetic field of the stator.
6.2 Electric Motors The conductor that rotates between the stationary magnetic field poles of the stator is called the "____."
Rotor or Armature The conductor that rotates between the stationary magnetic field poles of the stator is called the " rotor or armature."
6.1 Basic Electric Meters DC ammeter of the direct connection type must be connected in ____ with the power source and the load. If connected in reverse polarity, the coil will move in the opposite direction.
Series DC ammeter of the direct connection type must be connected in "series" with the power source and the load. If connected in reverse polarity, the coil will move in the opposite direction.
9.3 Conductance Conductance or conductivity is the property of metal that permits current to flow. The best conductors in order of their conductivity are: ____.
Silver, copper, gold, and aluminum.
6.2 Electric Motors The stationary magnetic field of a DC motor, called a "____," is a permanent magnet or an electromagnet.
Stator The stationary magnetic field of a DC motor, called a "stator," is a permanent magnet or an electromagnet.
10 - Introduction A series circuit is a circuit in which a specific amount of current leaves the voltage source and flows through every electrical device in a single path before it returns to the voltage source. True or False?
True
10.2 Understanding Series Calculations Resistance opposes the flow of electrons. In a series circuit, the total circuit resistance is equal to the sum of all the resistances in a series. True or False?
True
10.2 Understanding Series Calculations Kirchoff's Voltage Law states, "In a series circuit, the sum of the voltage drops across all of the resistors equals the applied voltage." True or False?
True
10.2 Understanding Series Calculations No matter how many resistances there are in a series circuit, the sum of the voltages across all of the resistances equals the voltage of the source according to the Law of Proportion. True or False?
True
10.2 Understanding Series Calculations The opposition to current flow results in a voltage drop of the circuit voltage. True or False?
True
7.2 Electron Current Flow Theory According to the Electron Current Flow Theory, electrons flow away from the negative terminal of the source, through the circuit and load, toward the positive terminal of the source. True or False?
True According to the "Electron Current Flow Theory," current always flows from the negative terminal of the source (where there is an excess of electrons), through the circuit and load, to the positive terminal of the source (where there is a deficiency of electrons).
9.4 Circuit Resistance Often the resistance of the power source and conductor are ignored in circuit calculations. True or False?
True Because the resistance of the power source and conductor is so much smaller than that of the load, they are generally ignored in circuit calculations.
9.3 Conductance Conductance is the property that permits current to flow. True or False?
True Conductance or conductivity is the property of a metal that permits currents to flow.
9.3 Conductance Conductance is the property that permits current to flow. True or False?
True Conductance or conductivity is the property of metal that permits current to flow.
7.3 Conventional Current Flow Theory According to the Conventional Current Flow Theory, positive charge flows from the positive to negative in the circuit. True or False?
True Conventional Current Flow Theory is a method of explaining current flow that focuses on the flow of "positive charge" rather than the flow of electrons.
7.7 Power DC power is determined by multiplying the Electromotive Force by the circuit intensity. True or False?
True DC power is determined by multiplying the Electromotive Force by the circuit intensity (P=ExI).
9.2 Power Source Direct current is used for electroplating, street trolley and railway systems, or where a smooth and wide radge of speed control is required for a motor-driven application. True or False?
True Direct current is used for electroplating, street trolley and railway systems, or where a smooth and wide radge of speed control is required for a motor-driven application. Direct current is also used for control Circuits and electronic instruments.
5.3 Field Interaction If a conductor carrying current is next to another conductor carrying current in the opposite direction, the electromagnetic field attempts to push the conductor apart. True or False?
True If a conductor carrying current is next to another conductor carrying current in the opposite direction, the electromagnetic field attempts to push the conductor apart.
5.4 Field Interaction Loops If a conductor is twisted to form a loop, electromagnetic fields around the conductor are compressed to create a dense and strong electromagnetic field. True or False?
True If a conductor is twisted to form a loop, electromagnetic fields around the conductor are compressed to create a dense and strong electromagnetic field.
5.5 Electromagnetism in a Coil If conductor loops are wound in the same direction, the conductor's electromagnetic fields add together. True or False?
True If conductor loops are wound in the same direction, the conductor's electromagnetic fields add together.
9.2 Power Source The major advantage of ac over dc is the ease of voltage regulation by the use of a transformer. True or False?
True In ac power a transformer can be used to either "step up" or "step down" the voltage, through electromagnetism.
7.7 Power Power is not equal to E x I for ac circuits because consideration must be given to inductive reactance. True or False?
True Power is not equal to E x I for ac circuits because consideration must be given to inductive reactance (the relationship between the voltage sin wave and the current sin wave). I.E. electromagnetic resistance.
7.5 Resistance Smaller conductors have a greater resistance and larger conductors have lower resistance. True or False?
True Smaller conductors have a greater resistance and larger conductors have a lower resistance.
8.8 Squaring a Number Squaring a number means multiplying the number by itself. True or False?
True Squaring a number means multiplying the number by itself. 10 x 10 = 100 23 x 23 = 529
7.1 The Electrical Circuit The work that can be performed by the moving electrons dependants on the circuit pressure and the circuit's opposition to the flow of electrons. True or False?
True The amount of electrical work that can be performed by an electrical circuit and the quantity of electrons that are forced to move (amperes) to produce work (watts) is dependent on the circuit pressure (voltage) and the circuit's opposition to the flow of electrons (resistance).
5.6 Magnetic Core The electromagnetic field of a coil can be made stronger by placing a soft iron core inside the coil windings. True or False?
True The electromagnetic field of a coil can be made stronger by placing a soft iron core inside the coil windings.
5.7 Amperes and Turns The strength of an electromagnetic field depends on the magnitude of the current and the number of turns in the electromagnet coil. True or False?
True The strength of an electromagnetic field depends on the magnitude of the current and the number of turns in the electromagnet coil.
9.2 Power Source Direct current is used for electroplating, street trolley and railway systems, or where a smooth and wide range of speed control is required for a motor-driven application. True or False
True Those are all uses for dc power as well as many electronics.
5.3 Field Interaction When conductors carrying current in the same direction are brought together, the electromagnetic fields attempt to pull the conductors together. True or False?
True When conductors carrying current in the same direction are brought together, the electromagnetic fields attempt to pull the conductors together.
9.10 Using the Formula Wheel When working any formula, the key to finding the correct answer is to follow these four steps: Step 1:Knowing what the question is asking you to find. Step 2:Determine the knowns of the circuit. Step 3:Select the formula. Step 4:Work out the formula calculation. True or False?
True When working any formula, the key to finding the correct answer is to follow these four steps: Step 1:Knowing what the question is asking for: I, E, R, or P. Step 2:Determine the knowns: I, E, R, or P. Step 3:Determine which of the formula wheel applies: I, E, R, or P and select the formula from the section based on what you know. Step 4:Work out the formula calculation.
6.4 Electromagnetic Relay An electromagnetic relay is a switch that uses an electromagnetic field to open or close its contacts. One part of the contact is fixed and the other moves by the attraction of the magnetic field. True or False?
True An electromagnetic relay is a switch that uses an electromagnetic field to open or close its contacts. One part of the contact is fixed and the other moves by attraction of the electromagnetic field.
9.9 Formula Wheel The formulas in the formula wheel apply to ____.
dc ac with unity power factor
9.11 Power Losses of Conductors Power in a circuit can be either "useful" or "wasted." Wasted work is still energy used; therefore it must be paid for, so we call this "____."
power losses Wasted work is still energy used; therefore it must be paid for, so we call this "power losses." The heating of conductors, transformers, and motor windings is wasted work.
9.1 Electrical Circuit An electrical circuit consists of the ____.
power source conductor load
9.4 Circuit Resistance The circuit resistance includes the resistance of the ____.
power source conductors load The total resistance of a circuit includes the resistance of the "power supply, the circuit wiring, and the load."
9.6 Ohm's Law and Alternating Current In an ac current, the factors that oppose current flow are____.
resistance inductive reactance capacitive reactance
10.1 Practical Uses of a Series Circuit Series circuits are often used for ____ applications.
signal and control
10.2 Understanding Series Calculations Kirchoff's Current Law states, " In a series circuit, the current is ____ through the transformer, the conductors, and the appliance.
the same In a series circuit current stays the same.
