AC Systems
2500 W (P = I^2 x R) (P=10^2 x 25)
A heating element in a heater has a resistance of 25 ohms and draws a current of 10 amperes. How much power is dissipated in the heater?
the peak value
A measurement taken from zero to the highest value obtained in either the positive or negative half of a sine wave would determine ? .
3%
The NEC recommends that voltage drops on branch circuits not exceeding ? at the farthest outlet of power, for heating or lighting loads, will provide for reasonable efficiency of operation
263.3 V
A motor was overheating because of low voltage at its terminals. A transformer was installed to correct the problem. What is the secondary voltage of the transformer required to be in order to supply 240 volts to the motor? (Round the FINAL answer to one decimal place.)
True
Alternating current is used to supply over 90% of the world's electrical power requirements.
0.8
Determine the cosine of angle theta. (Round the FINAL answer to one decimal place.)
75 V
Solve for the voltage across R2
Drag the terms below to the appropriate locations to properly label the sides of the impedance triangle
.
1.) Positive 2.) Positive 3.) Positive 4.) Zero
1.) Match the correct word to accurately complete the sentences below. In an AC circuit, when both the current and voltage of the circuit have a negative value, the power of this circuit is ? . 2.) In an AC circuit, when both the current and voltage of the circuit have a positive value, the power of this circuit is ? . 3.) In an AC circuit, when current of the circuit is ? and the voltage of the circuit is negative, the power of this circuit has a negative value. 4.) In an AC circuit, when the current of the circuit is negative and the voltage of the circuit is zero, the power of this circuit has a ? value.
Inductive Reactance
? is the induction of voltage or CEMF that opposes the current flow in a coil.
Instantaneous
? power in a circuit is the voltage at a certain instant multiplied by the current at that same instant. Select one: a.Average b.Effective c.Instantaneous d.RMS
4.167 A (I=P/E) (I= 1000/240)
A 1,000-watt lamp operates on 240 volts. How much current does it draw? (Round the FINAL answer to three decimal places.)
12 A I = E/R = 120/10 =12A
A circuit has a resistance of 10 ohms and a voltage of 120 volts. How much current flows?
20A I = E/Z = 100/5 = 20A
A circuit has an impedance of 5 ohms and a voltage of 100 volts. What is the current flow?
101.8 V E1 = Epeak x Sin 0 = 144 x 0.707 = 101.82 = 101.8 V
A sine wave has a maximum voltage (peak) of 144 V. What is the voltage at 45° of rotation? (Round the FINAL answer to one decimal place.)
resultant
A single vector produced from combining two or more vectors is called the ? .
all of the above
Conductor resistance causes a(n) ? between the voltage source and the connected load. Select one: a.decrease in current b.power loss c.voltage drop d.all of the above
in
Current and voltage in an AC resistive circuit are ? phase.
all of the above
Current passing through a resistance produces ? . Select one: a.a dissipation of power b.a voltage drop c.heat d.all of the above
10
Calculate the horizontal component of vector V1.
0
Calculate the horizontal component of vector V2.
-4
Calculate the horizontal component of vector V3.
-6
Calculate the vertical component of vector V4.
transformers
AC is converted from one level of voltage for transmission and then reduced to a different level of voltage for utilization by the end-user by using ? .
True
Alternating current flowing through a coil is opposed by two factors, resistance (R) and inductive reactance (XL).
True
An AC waveform will cross the zero axis, but a DC waveform will not cross it. Select one: True False
Electrons
An electric current is defined as the flow of ? through a conductor.
Reactive
An electrical measurement called VARs is used to measure ? power. Select one: a.apparent b.peak c.reactive d.true
the RMS value
Another name for the effective value is the ? .
180°
As a generator armature makes one full revolution, it goes through ? of mechanical rotation.
Increase
As frequency increases, skin effect ? . Select one: a.increases b.decreases c.stays the same
0°, 180°, 360°
At what degrees on the sine wave is the voltage equal to zero?
A vector that has the initial point at (0, 0) is in the ? position. a.minimum b.neutral c.standard d.zero
C. Standard
36.87 0- = Tan ^-1 0.75 =36.87
Determine the angle theta. (Round the FINAL answer to two decimal places.)
Initial point (-2, -5), terminal point (6, 5)
Determine the initial and terminal points of vector V1. Select one: a.Initial point (-5, -2), terminal point (5, 6) b.Initial point (-2, -5), terminal point (6, 5) c.Initial point (5, 6), terminal point (-5, -2) d.Initial point (6, 5), terminal point (-2, -5)
Current Curving up first and then curving down
Drag the appropriate current sine wave to the correct location to show an in-phase relationship.
True True False
Drag the terms True or False for the following statements.
B. increase
Factors such as skin effect and eddy currents are present in an AC circuit and, in practice, ? the resistance of the conductor. Select one: a.decrease b.increase c.do not affect
120 V RMS = Effective
Give the RMS value for 120 VAC effective
108 V Eavg = E peak x 0.637 =170 x 0.637 = 108 V
Give the average value for 120 VAC effective. (Round the FINAL answer to the nearest whole number.)
170 VAC Epeak = Eeff x 1.414 = 120 x 1.414 = 169.68 rounds to 170 VAC
Give the peak value for 120 VAC effective. (Round the FINAL answer to the nearest whole number.)
339 V Epeak- to - peak = 2x Epeak = 2x 169.68 = 339.36 =339 V
Give the peak-to-peak value for 120 VAC effective. (Round the FINAL answer to the nearest whole number.)
Epeak = E(p-p)/2 =600.00/2 =300 E(eff)=E(peak) x sin (45) = 300 x sin(45) = 212.132034 P = E(eff^2)/R =212.13^2/20.00 =2249.9999
Given the circuit, solve for the following: (Round the FINAL answer to two decimal places, if needed.) What is the peak voltage for the circuit? _____ Volts What is the effective voltage for the circuit? ______Volts What is the total power or wattage of the circuit? ____ Watts
1.) Eeff = Epk x .707 =42.40 x .707 = 29.9767 29.98 volts 2.) R2 = Epk / I (r2-pk) = 42.40/0.0090 =4711.1111 4711 omega 3.) I(r1pk) = Epk/R1 =42.40/5600.00 =0.007571428 =7.57 mA 4.) I(teff) = (Ir1pk + Ir2-pk) x 0.707 =(0.0075714285714290 +0.0090) X 0.7O7 =0.011716000000000303 =11.72mA 5.) Peff = Eeff x I(teff) =29.98 x 0.0117160 =0.3512081888 =351 mW
Given the circuit, solve for the following: (Round the FINAL answers to two decimal places.) The parallel circuit has 42.4 peak volts applied, a given R1 resistance of 5,600 ohms, and a peak current through R2 of 9 milliamperes. 1. What is the effective voltage? _______ Volts 2. What is the resistance of R2? 3. What is the peak current through R1? 4. What is the total effective current? 5. What is the effective power consumed by this circuit?
I inst= I peak x sin0
How can instantaneous AC current values be determined? Select one:
d. III or IV
How could you correct a voltage drop problem involving two rows of fluorescent fixtures fed from the same circuit in a practical manner? I. Change the fluorescent fixtures to incandescent light fixtures. II. Install a lighting panel closer to the fixtures. III. Install larger wire. IV. Put each row of fixtures on a separate circuit.
0 W Pshort = Ishort^2 x R =252^2 x 0 =0
How much power is consumed by the load under short-circuit conditions? All voltage sources contain internal resistance that is usually ignored in calculations because the resistive value of the load is so much greater than the resistance of the source. This is not always the case. (RB represents the battery's internal resistance.)
5 V Evd = Esource - Eload =240-235 =5v
If a generator voltage is 240 volts, and the load voltage is 235 volts, how much voltage is dropped on the line?
32 V Eavg = Epeak x 0.637 = 50x 0.637 = 31.85 V = 32V
If the AC voltage input to a full-wave rectifier is 100 volts peak to peak, what is the average DC voltage value? (Round the FINAL answer to the nearest whole number.)
Increase / decrease
If the voltage in a given circuit is increased, the current will ? , but if the resistance is increased, then the current will ? .
C. A single/both
In a direct current (DC) circuit, the current flows in ? direction, but in an alternating current (AC) circuit, current flows in ? direction(s). Select one: a.a negative / a positive b.a positive / a negative c.a single / both d.the forward / the reverse
True
In a parallel circuit, the total current equals the sum of the current of the loads.
B. Current/Voltage
In a pure resistive circuit, the true power (or watts) is equal to the product of the ? and ? . Select one: a.current / resistance b.current / voltage c.voltage / resistance d.reactance / current
all of the above
In an AC circuit, ? will oppose current flow. Select one: a.eddy currents b.resistance c.skin effect d.all of the above
The direction at which the conductor cuts the flux field changes as it rotates.
In an AC generator, what changes to cause polarity changes?
D. Voltage/ ExI
In order to lower power loss by reducing the current, one must raise the ? by the same proportion as one lowers the current to deliver the same amount of power to the user. This is expressed mathematically as P = ? .
True
It is theoretically possible for a circuit to be energized at 240 volts and have 100 amperes flowing and yet consume no power. Select one: True False
Lesson 2
Lesson 2
parallel / series
Loads are normally connected in ? with the source, and the resistance of the line is in ? with the source.
Average voltage D Effective voltage (RMS) C Peak-to-peak voltage A Peak voltageAnswer B
Match the points on the sine wave that indicate the values in the table. Average voltage Effective voltage (RMS) Peak-to-peak voltage Peak voltageAnswer
764
One horsepower equals ? watts.
Apparent, True
Power factor is a numeric ratio applied to the ? power to yield the ? power. Select one: a.apparent, true b.reactive, true c.true, apparent d.true, reactive
cosine
Power factor is the ? of angle Ө in the impedance triangle. Select one: a.cosine b.sine c.tangent d.All of the above
z= (square root Xl^2 +R^2)
Select the equation for determining the total impedance in an inductive and resistive circuit.
are Not
Skin effect and eddy currents ? present in a DC circuit, and, therefore, will not be factors that affect the opposition to current flow in a DC circuit. Select one: a.are b.are not
Reduced
Skin effect can be ? by using stranded conductors, which provide greater surface area for current than solid conductors. Select one: a.reduced b.increased
True
Skin effect increases the effective resistance of the conductor.
eddy currents
Skin effect is caused by induced ? from the AC current flow, which cause the electrons to be repelled toward the outer surface of the conductor.
0.0109 A
Solve circuit to find IR1. (Round the FINAL answer to four decimal places.)
Average
The ? value is the actual average of all the instantaneous voltage or current values across a full cycle of a rectified sine wave. a.average b.effective c.peak d.RMS
679 V Epeak = Eeff x 1.414 = 480 x1.414 =678.72 =679 V
The effective voltage is 480 volts. What is the peak voltage? (Round FINAL answer to the nearest whole number.)
P= Ex I
The equation for finding power in a circuit when the current and voltage are known is ? .
VARS =E(L) x I(L) VARS = E(L^2)/X(L) VARS = I(L^2) x X(L) ALL OF THE ABOVE!!!
The equation to find the VARs in an inductive circuit is ? .
False VARs = E(l) x I(l) In a circuit containing reactance, true power can be calculated by the formula: P = E x I x PF The correct answer is 'False'.
The power formula P = E x I applies in all cases. Select one: True False Note: This applies only in DC circuits and AC circuits when the current and voltage are in-phase, or in a purely resistive circuit where there is no reactive power. Reactive power can be calculated by the formula:
B. impedance/Z
The total current-limiting effect of an inductor is called ? and is symbolized by the letter ? . Select one: a. counter electromotive force / C b.impedance / Z c.inductive reactance / X d.resistance / R
True
The total current-limiting effect of the inductor is a combination of the inductive reactance and resistance of the inductor.
False Note: Total circuit power = 636 W. Power of the loads = 623 W; 13 W of power is dissipated as heat in the circuit conductors. The correct answer is 'False'.
The total power consumed by the circuit is equal to the power consumed by the loads.
Resistance
The true power, in watts, consumed by the circuit is consumed by the ? of the circuit. Select one: a.impedance b.reactance c.resistance d.all of the above
ampere/A
The unit of electric current is the ? , which is represented by the letter ? .
volt / V
The unit of electrical potential is the ? , which is represented by the letter ? .
False
The waveforms will have the same heating effect on a resistor.
45 degree
These sine waves indicate voltage and current ? out-of-phase.
12
Two rows of fluorescent lamps are installed in an office on the same branch circuit, with each row drawing 12.5 amperes. The source voltage is 277 volts, and the line resistance is 0.5 Ω. The wire used has a constant (k) of 12.6. If the load is 129 feet from the source, what is the specific wire size used in this installation? (Assume 75°C wire.) Wire size = ____ AWG
10
Two rows of fluorescent lamps are installed in an office on the same branch circuit, with each row drawing 12.5 amperes. The source voltage is 277 volts, and the line resistance is 0.5 Ω. The wire used has a constant (k) of 12.6. If the load is 130 feet from the source, what size wire would you need to install for this circuit to meet the recommendations of the NEC for acceptable voltage drop on a branch circuit? (Assume 75°C wire)Wire size = ____ AWG
False
Two rows of fluorescent lamps are installed in an office on the same branch circuit, with each row drawing 12.5 amperes. The source voltage is 277 volts, and the line resistance is 0.5 Ω. The wire used has a constant (k) of 12.6. The voltage drop will be within the recommendation of the NEC.
4.5% % VD = Evd/Es x 100 =12.5/277 x 100 = 4.5%
Two rows of fluorescent lamps are installed in an office on the same branch circuit, with each row drawing 12.5 amperes. The source voltage is 277 volts, and the total line resistance of the circuit conductors is 0.5 Ω. The wire used has a constant (k) of 12.6. What is the percentage of voltage drop? (Round the FINAL answer to one decimal place.)
264.5 V
Two rows of fluorescent lamps are installed in an office on the same branch circuit, with each row drawing 12.5 amperes. The source voltage is 277 volts, and the total line resistance of the circuit conductors is 0.5 Ω. The wire used has a constant (k) of 12.6. What is the voltage at the load? (Round the FINAL answer to one decimal place.)
0.817 A R100w = Es^2/P = 120 ^2/100 = 144 ohm I100w = Eload/R100w = 117.67/144 =0.817 A
Use the diagram to determine the current of each 100 W lamp. (Round the FINAL answer to three decimal places.)
0.613 A R75w = Es^2/P = 120 ^2/75 = 192 ohm I 75w = Eload/R 75w = 117.67/192 =0.613 A
Use the diagram to determine the current of the 75 W lamp. (Round the FINAL answer to three decimal places.)
3.11 A Rm= E^2/Pm = 120^2/(746x0.5) =38.60589812 ohm I m = E load/Rm = 117.67/38.60589812 = 3.05 A
Use the diagram to determine the current of the motor. (Round the FINAL answer to two decimal places.)
P 100w = Eload x I 100w = 117.67x0.817 =96 W
Use the diagram to determine the power consumed by each of the 100 W lamps. (Round the FINAL answer to the nearest whole number.)
706 W I = E/Rb + Rm = 12.6/0.05+0.025 =168A P= I ^2 x R =168^2 x 0.023 = 706W
Use the diagram to determine the power consumed by the motor when the push button is depressed. (Round the FINAL answer to the nearest whole number.)
I = E/Rb + Rm =12.6/0.05 +0.1 =84A P= I ^2 x R =84^2 x 0.1 = 706W
Use the diagram to determine the power consumed by the motor when the push button is depressed. (Round the FINAL answer to the nearest whole number.)
794W I = E/Rb + Rm =12.6/0.05 +0.050 =126A P= I ^2 x R =126^2 x 0.050 = 794 W
Use the diagram to determine the power consumed by the motor when the push button is depressed. (Round the FINAL answer to the nearest whole number.) Note: All voltage sources contain internal resistance that is usually ignored in calculations because the resistive value of the load is so much greater than the resistance of the source. This is not always the case. (RB represents the battery's internal resistance.)
358.9 W Pm = Eload x Im = 117.67 x 3.05 =358.9 W
Use the diagram to determine the power consumed by the motor. (Round the FINAL answer to one decimal place.)
Pline = I t^2 x Rline = 5.3^2 x 0.44 = 12.36 W
Use the diagram to determine the power loss in the conductors. (Round the FINAL answer to two decimal places.) Use the diagram to determine the power loss in the conductors. (Round the FINAL answer to two decimal places.)
5.3 A I loads = Im +I(100w) +I(100w) +I(75w) =3.05+0.817+0.817+0.613 =5.3 A
Use the diagram to determine the total current of the loads. (Round the FINAL answer to one decimal place.)
636W Pt = Es x I loads = 120x 5.3 636 W
Use the diagram to determine the total power consumed by the circuit.
9.3 V It = Et/ (Rb _+ Rm) = 12.6/(0.05+0.14) = 66.3 A Eb = It x Rb = 66.3 x 0.05 = 3.3 V Em = Et-Eb 12.6 - 3.3 9.3 V
Use the diagram to determine the voltage across the load when the push button is depressed. (Round the FINAL answer to one decimal place.) All voltage sources contain internal resistance that is usually ignored in calculations because the resistive value of the load is so much greater than the resistance of the source. This is not always the case. (RB represents the battery's internal resistance.)
117.67 V Eload=Eg - Eline = 120 - 2.33 = 117.67 V
Use the diagram to determine the voltage at the load after calculating the voltage drop of the wire.
112.72 V E0.1= Il x R0.1 =2.2 x0.1 =0.22V El = Em - E0.1- E0.1 =113.16 - 0.22 - 0.22 =112.72 V
Use the diagram to determine the voltage drop across load L. (Round the FINAL answer to two decimal places.)
113.16 V Im +l = Im + Il = 1.5 +2.2 =3.7 A Eo.2 = Im+l x R0.02 = 3.7 x 0.2 =.74 V Em = Er-Eo.2-Eo.2 =114.64-.74-.74 =113.16 V
Use the diagram to determine the voltage drop across load M. (Round the FINAL answer to two decimal places.)
It = Ir +Im +Il = 3+1.5+2.2 = 6.7A E 0.4= I(t) x R(0.4) =6.7 x 0.4 =2.68 V Er = Es - E 0.4 - E0.4 =120 - 2.68 -2.68 = 114.64 V
Use the diagram to determine the voltage drop across the resistor R. (Round the FINAL answer to two decimal places.)
2.33 V Eline = It x (Ra + Rb) =5.3 x 0.44 2.33 V
Use the diagram to determine the voltage drop of the conductors. (Round the FINAL answer to two decimal places.)
5.3 A It = Es/Rt = 120/22.7 = 5.3A
Use the diagram to determine total current. (Round the FINAL answer to one decimal place.)
22.7 Omh Ra and Rb represent the resistance of the wire. The 120 volts of the motor and lamps is their rated voltage and not the actual voltage.
Use the diagram to determine total resistance. (Round the FINAL answer to one decimal place.) Note: Use the rated voltage and wattage to determine resistance.
Inductive/inductive
VARs are equal to the amount of current flowing through a(n) ? part of a circuit times the voltage applied to the ? part of the circuit.
The correct answer is: 0° = ? amps → 0, 30° = ? amps → 5, 45° = ? amps → 7.07, 60° = ? amps → 8.66, 180° = ? amps → 0
What is the instantaneous value of a 10 ampere peak sine wave at 0, 30, 45, 60, and 180 degrees? 0° = ? amps 30° = ? amps 45° = ? amps 60° = ? amps 180° = ? amps
71 VAC Epeak = Eeff x 1.414 = 50 x 1.414 = 70.7 VAC 71 VAC
What is the peak voltage value of an AC power source with an effective value of 50 volts? (Round the FINAL answer to the nearest whole number.)
100 V Epeak-to-peak = Epeak x 2 = 50 x 2 = 100 V peak to peak = 100 V
What is the peak-to-peak value of the AC voltage wave?
2.1% %VD = Evd/Es x 100 = 5/240 x 100 = 2.1%
What is the percentage of voltage drop if you have 235 volts at a load fed from a 240-volt source? (Round the FINAL answer to one decimal place.)
0.05 omegas (ohms
What is the value of RL when the wattage is at peak?
10,000 : 1 Note: Voltage is not a consideration; power loss in a transmission line would be calculated by the formula P = I2 × R, 1,0002 = 1,000,000, 102 = 100, and 1,000,000 − 100 = 999,900. The higher current transmission line would have a power loss 10,000 times that of the lower current transmission line, given that the resistance of the conductors was the same.
What would be the ratio of power loss of a transmission line carrying 1,000 amperes at 1,000 volts as compared to 10 amperes at 100 kilovolts? Assume a resistance of 1 ohm on the transmission line.
I short circuit = Et/Rb =12.6/0.05 =252A
What would the current flow be if a short circuit is put across the battery's terminals? Note: All voltage sources contain internal resistance that is usually ignored in calculations because the resistive value of the load is so much greater than the resistance of the source. This is not always the case. (RB represents the battery's internal resistance.)
True
When a steady direct current flows through a coil, the only opposition to the flow of current is the resistance of the wire from which the coil is made.
RMS
When an AC voltage is given, it is always the ? value unless stated otherwise. Select one: a.average b.nominal c.peak d.RMS
True
When comparing AC to DC, it is easier to transform an AC voltage. Select one: True False
d. resistance / current
When distributed by transmission lines, power loss is due to the ? of the wire that generates heat in the conductor. The heat is generated as a result of ? flowing through the conductor.
180°, 360°
When is the voltage on an AC sine wave at the maximum positive and maximum negative value?
True
When referring to values of AC voltages or currents, the letters RMS stand for Root Mean Square.
P open = I^2 x R = 0^2 x infinite sign = 0w
When the battery terminals are open, how much power is consumed by the load?
in-phase
When the current and the voltage sine waves are ? , they both have the same frequency, crossing the reference line at the same time and going in the same direction.
out of phase
When the current and voltage are ? , one may be positive while the other is negative. Select one: a.in-phase b.out-of-phase c.None of the above
maximum/in-phase
When the current and voltage are ? , one may be positive while the other is negative. Select one: a.in-phase b.out-of-phase c.None of the above
90 degrees
When the current and voltage are ? out-of-phase, the power consumed is zero watts. Select one: a.0° b.45° c.90° d.180°
E= I x R
Which equation expresses Ohm's Law in its simplest form?
100 Ω
Find the total resistance in the following circuit.
582.8 Ω (Rt + R2 + ...+Rn) ( 100+470+12.8) = 582.8
Find the total resistance in the following circuit.
0
For this question you will be working to determine a single, equivalent resultant vector. To add the six vectors you will first find the horizontal and vertical components of each vector. The next step will be to combine like vertical and horizontal values vectorially where then you can apply the Pythagorean Theorem to determine a single equivalent resultant vector. Use the table to track your progress. Calculate the vertical component of vector V1.
counterclockwise
From 0° on the X (horizontal) axis, the positive vector angle positions are rotated in the ? direction.
186.5 W (P=746xHP) (746 x 1/4)
How much power is required by a 1/4-hp motor? (Neglect I2R losses.)
Initial point (2, 2), terminal point (-3, 8)
Determine the initial and terminal points of vector V2. Select one: a.Initial point (-8, 3), terminal point (-2, 2) b.Initial point (-3, 8), terminal point (-2, 2) c.Initial point (-2, 2), terminal point (-3, 8) d.Initial point (2, 2), terminal point (-3, 8)
0.6 sin = o/h
Determine the sine of angle theta. (Round the FINAL answer to one decimal place.)
0.75 Tan=O/A =12/16 =0.75
Determine the tangent of angle theta. (Round the FINAL answer to two decimal places.)
Top left Terminal , Bottom right Initial
Drag and locate the appropriate term to properly label the vector's start and end point.
See definition
Each of the vectors below have a magnitude of 10. Drag the appropriate angle value to the space next to the correct vector to indicate it's direction.
reverses direction
Each time the generated voltage within a generator alternator reverses polarity, the current in an external circuit connected through slip rings to the generator alternator ? .
False
In this circuit, four 120-volt/100-watt lamps are connected in parallel. Each lamp will not have a 120-volt drop across it and, therefore, will not dissipate the 100 watts of power it is rated for.
Note: The Pythagorean Theorem method is used with the triangle method.
Match the name of the method shown for solving for two vectors at right angles to each other next to the images below.
True
One possible method to solve for the resultant of vectors V1 and V2 is the triangle method.
Resistance/Ω
Opposition to current flow is called ___? the unit of which is represented by the symbol ____?
True
Peak-to-peak, Peak, RMS, and Average are four forms of measurement of voltage and current associated with sine waves.
True
Power in a circuit is the amount of work being done per unit of time.
57.36 Vy = Sin 35 x 100
Reduce the vector shown to it's (Y) vertical component. (Round the FINAL answer to two decimal places.)
81.92 Vx = Cos 35 x 100
Reduce the vector shown to its (X) horizontal component. (Round the FINAL answer to two decimal places.)
50% / 75% P= I^2 x R Reducing R by one half reduces power loss by 50%Reducing I by one half reduces power loss by 75% The correct answer is: 50% / 75%
Reducing the resistance of the wire by one-half will reduce power loss by ? , but reducing the current by one-half will reduce the power loss by ? .
False Skin effect is a result of alternating current; it is directly proportional to frequency. The higher the frequency, the greater the skin effect.
Skin effect is smaller at high frequencies.
2.182 A
Solve for the current in the circuit. (Round the FINAL answer to three decimal places.)
0.25 A Rt = R1 + R2 + R3 =27 + 82+ 51 = 160 OHM It = Et/Rt = 40/160 =0.25 A
Solve for the current through R1 in the following circui
100 Ω R2,3,4 = R/N (75/3 =25 OMH) Rt= R2,3,,4 Rt = 75+25 = 100 omh
Solve for the current through R1 in the following circuit
1.6 A Ir1 = Es/R1 = 500/312.5 = 1.6A
Solve for the current through R1 in the following circuit.
120
Solve for the unknown value (E) in the circuit.
250
Solve for the unknown value in the following circuit. (Hint: Electrical equations are designed to be solved in base units, amps, ohms, volts or watts.)
5.5 V E r3 = I r3 x R3 = 0.05 x 110 = 5.5 V Er2 = Er3 = 5.5 V
Solve for the voltage across R2
275 V E r2 = I r2 x R2 = 12.5 x 22 = 275 V
Solve for the voltage across R2.
: 5536 Ω
Solve the circuit to find the total resistance. (Round the FINAL answer to the nearest whole number of ohms.) The resistance values are in kilo-ohms (1000 ohms). Note: The values calculated for this question will be used for additional questions.
RMS value
The ? is the value of AC voltage that produces the same amount of power as a like value of DC voltage.
sine wave
The AC voltage waveform is in the positive direction for some period of time and in the negative direction for some period of time. What is the name given to this waveform?
15 W (P=ExI) (P=12 x 1.25)
The current through a lamp is 1.25 amperes when the lamp is connected to a 12-volt battery. How much power is consumed by the lamp?
a 2-amp positive DC current
The current waveform shown is an example of a(n) ? .
60 / 60 / 1
The most common frequency in the United States is ? Hz, which means the voltage waveform completes ? cycles in ? second(s).
120 V Eeff = Epeak x .707 = 170 x 0.707 = 120 V
The peak voltage is measured and found to be 170 volts. What is the effective voltage? (Round the FINAL answer to the nearest whole number.)
2
The peak-to-peak value is equal to ? time(s) the peak value.
the sine of the angle of rotation
The plotted resulting waveform as the conductor rotates in a magnetic field follows ? .
P + I^2 x R
The power loss in a conductor can be expressed mathematically as ? .
resistance / current
The power loss of a transmission line can be reduced by either reducing the ? of the wire or the amount of ? .
watt/ W
The unit of electrical power is the ? , whose symbol is ? ,
True
The vectors V1 and V2 could be added by using the parallelogram method or the triangle method.
True
The vectors V1 and V2 could be added by using the parallelogram method.
b. Cosine/Sine
To determine a vector's X (horizontal) and Y (vertical) components when the magnitude and direction (angle) are known, one typically uses the function ? to find the X and ? to find the Y components. a.sine / cosine b.cosine / sine c.tangent / sine d.cosine / tangent
The direction of a vector is indicated by an arrowhead on the end of the line segment. Select one: True False
True
93
Use the Pythagorean Theorem to determine the value of the resultant Vr for the two vectors shown. (Round the FINAL answer to the nearest whole number.)
True
Using the electron theory, determine if the direction of current flow through each of the resistors and the polarity of the voltage drop across each of the resistors in the circuit is correct as indicated.
Added
Vectors can be ? using the parallelogram method.
0.01 seconds
What is the period for a frequency of 100 Hz? (Round the FINAL answer to two decimal places.)
t = 1/f t = 1/ 1,000,000 t= 0.000001 seconds 1.0E-6 seconds
What is the period for a frequency of 1MHz?
72.91 V Note: Up until now, we have calculated voltage drop by subtracting the calculated drop from the supply voltage. However, using the standard voltage drop formula, we assume that the device will be supplied by the full (supply) voltage and then use the load current in our calculation. In this problem, we are looking at what can happen to a circuit when the wire has been undersized and then calculating the actual voltage delivered to the load using Ohm 's Law as the basis of our calculation.
What voltage is delivered to a 120-volt/5,000-watt load that is fed with #10 AWG wire (1.24 ohms/1,000 feet) and located 750 feet from the 120-volt source? (Round the FINAL answer to two decimal places.)
Rt= R1 + R2 + R3....+ Rn
Which is the correct formula for determining total resistance in series circuits?
d. II Weight is a force. Although pounds of force can be applied in any direction when measuring weight, the force is in a down direction due to the pull of gravity. Weight is a vector.
Which of the following is a scalar quantity and not a vector?
I, II, and V
Which of the following represents a formula that can be used to find power? I. II. III. IV. V.
C. I and IV
Why is AC used in power distribution systems more often than DC?I. AC can be easily transformed to raise or lower levels of voltage and current for a given amount of power.II. AC is easier to produce than DC.III. AC is safer than DC.IV. AC transformers allow very high voltage values to deliver large amounts of power at low current levels. Select one: a.I. and II. b.I. and III. c.I. and IV. d.II. and IV.
x = 8, y = 10
Write the vector V1 in component form. Select one: a.x = -10, y = -8 b.x = -8, y = -10 c.x = 8, y = 10 d.x = 10, y = 8
x = -5, y = 6
Write the vector V2 in component form. Select one: a.x = -6, y = -5 b.x = -5, y = -6 c.x = -5, y = 6 d.x = 5, y = 6
Which of the following statements is true? Select one: a.Scalar quantities display both magnitude and direction of force. b.Vector quantities display both magnitude and direction of force. c.Both a. and b. are true. d.Neither a. or b. is true.
b.Vector quantities display both magnitude and direction of force.
The magnitude of both scalar and vector quantities are represented by the ? of a line. Select one: a.color b.direction c.length d.all of the above
length
