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Electrical Engineering
Electrical engineering is a field of engineering that deals with the study and application of electricity, electronics and electromagnetism.
23,056 Questions
Current in a parallel circuit?
In any parallel connection The original current gets divided into the parallel branches, however the division is solely based upon the resistances of the parallel paths. Current always tries to flow through the branch having the least resistance. Thus More current will flow in the branch having less resistance and vice-versa. The currents flowing in the parallel branches can be found out by using the current divider rule. Suppose if R1 & R2 are two branches of a parallel connection & i1 & i2 is the current flowing through them respectively. Let 'I' be the original current then the current through R1 can be given as
i1=R1/(R1+R2) * I similarly current through R2 can also be calculated.
What is the difference between a standard capacitor and a coupling capacitor?
Coupling capacitors are used to couple different stages so as to prevent DC from the o/p of one stage to go into the i/p of the next stage. For instance in coupling two BJT (bipolar junction transistors) it is required to use coupling capacitor to allow only ac signal from the o/p of fisrt stage to go to i/p of next BJT as incoming dc can distrub the biasing of the other BJT.
Bypass capacitors are used to bypass the ac signal to ground. A capacitor is connected b/w the gnd and the wire. For ac signal capacitor will behave as short and will bypass it. However dc will not be bypassed as capacitor will behave as open for DC.
Why refrigerator is called closed loop control system?
A closed loop system is one where the ouput of the system is at least part of the input. In a refrigerator, the output of the cooling system (the cold air inside the refrigerator) is measured, and is fed back into the system to determine whether the system needs to continue cooling.
An example of a fridge that was an open loop system would be one that turns on and cools for 1 hour every 6 hours, regardless of internal temperature.
A generator is a device that converts mechanical energy into electrical energy by electromagnetic induction - it "generates" (or creates) electricity.
A generator is a mechanical device which converts mechanical energy to electrical energy. Generators may be driven by a broad range of sources; steam turbines, electricity, petrol, or oil, natural gas, wind, and even water (hydroelectric).
What is the formula used to calculate electrical power in a dc circuit?
Electric power is a measure of energy per unit of time.
For example: 1 volt=1 joule (energy)/ 1 coulomb (electric charge)
1 ampere=1 coulomb/1 second
1 watt=1 joule/1 second
In a direct current circuit, P (watts)=V (volts) x I (amps)
For direct current:
P=VxI
P=I^2R
P=V^2/R
Where R is resistance (ohms).
For alternating current:
S=P+jQ
S=VI* (I* means complex conjugate of I)
S=sqrt(P^2+Q^2)
V=IxZ
Z=R+jX
So P is the real part of S and Q is the imaginary part of S.
S is in unit of volt-amperes, P is in watts and Q is in vars (volt-ampere reactive).
X is reactance and is calculated by either jwL or 1/jwC or both depending on what components are in the circuit.
w is 2xpixfrequency of the AC circuit. L is inductance and C is capacitance.
CommentThere is no such thing as 'electrical power'. Power is simply a rate -it is neither electrical, mechanical, or anything else!How can a composite signal be decomposed?
Spectral analysis of a repetitive waveform into a harmonic series can be done by Fourier analyis.
This idea is generalised in the Fourier transform which converts any function of time expressed as a into a transform function of frequency. The time function is generally real while the transform function, also known as a the spectrum, is generally complex.
A function and its Fourier transform are known as a Fourier transform pair, and the original function is the inverse transform of the spectrum.
1905 watt's ( the pf hasn't been indicated as leading or lagging) this is wrong. the answer is 1770 W its looking for a symplified answer if you dont know whether its leading or lagging use basic formula 220v * 5a * .7 = watts
What is effect of power factor on the readings of wattmeter?
If you are asking whether power-factor improvement has any effect on a wattmeter reading, then the answer is no, it doesn't. Improving the power factor of a load has absolutely no effect on the power of the load, but it can act to reduce the value of the load current.
What the difference between extraction and bleeding in steam turbine?
bleed is amount of steam output from turbine through pipe and exit from final stage of turbine . this bleed enter to feed water heater (low and high) and deaereator to increase unit efficiency
or rather bleed is the amount of steam drained out of the steam turbine during the expansion of steam and this rejected heat energy is used to heat the feed water supplied to the boiler...........
How do you give values to resistor color codes?
Resistor Colour Bands Explained
We need to know the difference between some different types in order to read the colour codes of resistors.
Where as "most" resistors commonly in use, uses four bands, there are others using five and even six bands.
It is not always easy to know which way to hold the resistor in order to read the code correctly.
On four band resistors, there is normally a gap between the first three and the last fourth band.
______ 1 2 3 4 5 6 ______ Example of a 4 band resistor Note that band 1,2,3 and 5 makes up the 4 in use
In this example the first 2 bands reads out the value directly.
The third band is used to tell you the multiplication factor.
First band is Brown. This is 1.
Second band is Red. This is 2.
This makes the number 12. Now for the multiplication factor.
Third band is Brown again. This is multiplication factor 10. We multiply the number 12 by 10.
The value of this particular resistor is 12x10 equals 120 Ohm.
(We can also think about brown as 1... One extra zero added to the answer. 12+0=120)
The 5th band tells us how accurate this value is! (tolerance of the resistor)
Gold indicate 5% accuracy.
See the schematics further down for more tolerances.
______ 1 2 3 4 5 6 ______ Example of a 5 band resistor Note that band 1,2,3,4 and 5 makes up the 5 in use
In this example the first 3 bands read out the value directly.
The 4th band is used to tell you the multiplication factor.
First band is Brown. This is 1.
Second band is Red. This is 2.
Third band is Black. This is 0.
This makes the number 120. Now for the multiplication factor.
4th band is Brown. This is multiplication factor 10. We multiply the number 120 by 10.
The value of this particular resistor is 120x10 equals 1200 Ohm.
(We can also think about brown as 1... One extra zero added to the answer. 120+0=1200)
The 5th band tells us how accurate this value is! (tolerance of the resistor)
See the schematics further down for these tolerances.
______ 1 2 3 4 5 6 ______ Example of a 6 band resistor Note that all bands 1 through 6 is in use
Brown, Red, Black; makes 120; multiply by brown (10) and you get 1200 Ohm.
5th band is Gold (1200 Ohm +-5% tolerance)
The value of the resistor so far follows the previous 5 band explanation
The 6th band only adds more information about the resistor.
This information is related to temperature (Temperature coefficient).
In other words, how much the value will increase or decrease depending on temperature.
(most resistors will have slightly increased resistance with increased temperature.)
Now that you know how to read the different bands on different resistors
it is time for the full chart of colours used on resistors.
Colour value MultiplierTolerance Temperature CoefficientSilver 0,01 Silver 10% Gold 0,1 Gold 5% Black 0 1 Brown 1 10 1% 100ppm Red 2 100 2% 50ppm Orange 3 1k 15ppm Yellow 4 10k 25ppm Green 5 100k 0,50% Blue 6 1M 0,25% Violet 7 10M 0,10% Gray 8 0,05% White 9
Note:
Some resistors may lack the band for tolerance alltogether. These resistors may be highly inaccurate and offers only 20% accuracy regarding their markings.
Note that the temperature coefficient is different for different values of resistors.
We calculate the temperature drift by dividing the resistor value by 1 million (That gives us 1 part of a million), then we multiply by the 6th band code value of which can be 15,25,50 or 100.
This gives us the drift in Ohm per degree Celsius.
Example 1:
A resistor of 10.000 Ohm (10KOhm) with a 6th ring being Red, we calculate the drift:
10.000/1.000.000*red (50) = 0,5.
The resistance will increase by 0,5 Ohm per degree Celsius.
If the temperature increases by 45 degree Celsius, the resistance will increase by 22,5 Ohm.
Example 2:
A resistor of 1.200 Ohm (1,2KOhm) with a 6th ring being Brown, we calculate the drift:
1.200/1.000.000*brown (100) = 0,12.
The resistance will increase by 0,12 Ohm per degree Celsius.
If the temperature increases by 45 degree Celsius, the resistance will increase by 5,4 Ohm.
This drift is normally added because resistance increase with temperature.
If you plan on making equipment that is used in colder environments like in outer space, then you subtract this drift.
It depends on where you are and where you want to go.
Note that ALL resistors have a temperature coefficient whether this is marked or not.
Resistors that are not marked with a 6th band for this, typically have a TC of 200ppm or more.
Resistors do not necessarily follow the pattern 100% through temperature changes.
A resistor of 10.000 Ohm may increase its value from 0-50oC and then decrease again from 50-100oC. It may even be the other way around, or even a completely different pattern.
A 6 band resistor will typically only increase in value from 0oC and upwards. 6 band resistors are very high quality resistors that are designed to be predictable.
Some information not written on the resistors:
Commercial grade: 0oC to 70oC
Industrial grade: -40oC to 85oC (sometimes -25oC to 85oC)
Military grade: -55oC to 125oC (sometimes -65oC to 275oC)
Standard Grade -5oC to 60oC
The Electronic Industries Association (EIA), and other authorities, specify standard values for resistors, sometimes referred to as the "preferred value" system, where the colour coding is the key to understanding all of them. The above explanation deals with them all.
(It should be noted that allthough EIA have specified standard values, this is only a common guideline. The colour coding can easily describe other values depending on spechial needs.)
Further information on the standard series might be of interest and is as follows:
E6 series 20% tolerance. 6 values between 100 and 1000 Ohm.
The two first bands are used for the value. The third band is used for the multiplier.
Fourth band is most often omitted on these, hence indicating only +/- 20% accuracy.
The standard values are:
100, 150, 220, 330, 470, 680 Ohm.
E12 10% tolerance. 12 values between 100 and 1000 Ohm.
The two first bands are used for the value. the third band is used for the multiplier.
Fourth band is normally Silver, which indicate +/- 10% accuracy, or Gold, which indicate +/- 5% accuracy.
The standard values are:
100, 120, 150, 180, 220, 270, 330, 390, 470, 560, 680, 820 Ohm.
E24 5% tolerance (and often 2% tolerance). 24 values between 100 and 1000 Ohm.
The two first bands are used for the value. the third band is used for the multiplier.
Fourth band is normally Gold, which indicate +/- 5% accuracy, or Red, which indicate +/- 2% accuracy.
The standard values are:
100, 110, 120, 130, 150, 160, 180, 200, 220, 240, 270, 300, 330, 360, 390, 430, 470, 510, 560, 620, 680, 750, 820, 910 Ohm.
E48 2% tolerance. 48 values between 100 and 1000 Ohm.
The three first bands are used for the value. the fourth band is used for the multiplier.
Fifth band is normally Red, which indicate +/- 2% accuracy, or Brown, which indicate +/- 1% accuracy.
These resistors may have a 6th band indicating temperature coefficient. Often Brown (100ppm) or Red (50ppm).
The standard values are:
100, 105, 110, 115, 121, 127, 133, 140, 147, 154, 162, 169, 178, 187, 196, 205, 215, 226, 237, 249, 261, 274, 287, 301, 316, 332, 348, 365, 383, 402, 422, 442, 464, 487, 511, 536, 562, 590, 619, 649, 681, 715, 750, 787, 825, 866, 909, 953
E96 1% tolerance. 96 values between 100 and 1000 Ohm.
The three first bands are used for the value. the fourth band is used for the multiplier.
Fifth band is normally Brown, which indicate +/- 1% accuracy. Green (0.5%), Blue (0.25%), Violet (0.1%) or Gray (0.05%) might be found.
These resistors often have a 6th band indicating temperature coefficient. Often Brown (100ppm), Red (50ppm), Orange (15ppm), Yellow(25ppm).
The standard values are:
100, 102, 105, 107, 110, 113, 115, 118, 120, 124, 127, 130, 133, 137, 140, 143, 150, 150, 154, 158, 162, 165, 169, 174, 180, 182, 187, 191, 196, 200, 205, 210, 220, 221, 226, 232, 237, 243, 249, 255, 267, 270, 274, 280, 287, 294, 301, 309, 324, 330, 332, 340, 348, 357, 365, 374, 390, 392, 402, 412, 422, 432, 442, 453, 470, 475, 487, 499, 511, 523, 536, 549, 560, 576, 590, 604, 619, 634, 649, 665, 680, 698, 715, 732, 750, 768, 787, 806, 820, 845, 866, 887, 909, 931, 953, 976 Ohm.
E192 0.5, 0.25, 0.1% and even higher tolerances.
The three first bands are used for the value. the fourth band is used for the multiplier.
Fifth band is normally Green, which indicate +/- 0.5% accuracy. Blue (0.25%), Violet (0.1%) or Gray (0.05%) might be found.
These resistors often have a 6th band indicating temperature coefficient. Often Brown (100ppm), Red (50ppm), Orange (15ppm), Yellow(25ppm).
The standard values are:
100, 101, 102, 104, 105, 106, 107, 109, 110, 111, 113, 114, 115, 117, 118, 120, 120, 123, 124, 126, 127, 129, 130, 132, 130, 135, 137, 138, 140, 142, 143, 145, 150, 149, 150, 152, 154, 156, 158, 160, 160, 164, 165, 167, 169, 172, 174, 176, 180, 180, 182, 184, 187, 189, 191, 193, 200, 198, 200, 203, 205, 208, 210, 213, 220, 218, 221, 223, 226, 229, 232, 234, 240, 240, 243, 246, 249, 252, 255, 258, 270, 264, 267, 271, 274, 277, 280, 284, 300, 291, 294, 298, 301, 305, 309, 312, 330, 320, 324, 328, 332, 336, 340, 344, 360, 352, 357, 361, 365, 370, 374, 379, 390, 388, 392, 397, 402, 407, 412, 417, 430, 427, 432, 437, 442, 448, 453, 459, 470, 470, 475, 481, 487, 493, 499, 505, 510, 517, 523, 530, 536, 542, 549, 556, 560, 569, 576, 583, 590, 597, 604, 612, 620, 626, 634, 642, 649, 657, 665, 673, 680, 690, 698, 706, 715, 723, 732, 741, 750, 759, 768, 777, 787, 796, 806, 816, 820, 835, 845, 856, 866, 876, 887, 898, 910, 920, 931, 942, 953, 965, 976, 988 Ohm.
Each ascending series provide increased tolerance and accuracy. Where as we in the "old" days used variable resistors to adjust circuitry, we can today mass-produce electronics with fewer, more accurate components, hence mostly eliminating the need of variable resistors for adjusting and tuning.
Here is a mnemonic device for remembering the band colors in order by multiplier value. It may seem a little racist, but no disrespect is intended; the use of the word "black" in reference to a black color band prevents it from being confused with blue or brown. This mnemonic device is so effective that I recalled it from memory even though I haven't read a resistor in over 15 years.
"Black boys rape our young girls, but Violet gives willingly."
Black --> Black
Boys --> Brown
Rape --> Red
Our --> Orange
Young --> Yellow
Girls --> Green
But --> Blue
Violet --> Violet
Gives --> Gray
Willingly --> White
-HW
Postcode for Kidderminster in the West Midlands, UK.
Also a vector group (connection configuration) of a 3-phase transformer.D - Means Delta Wound Primary
Y - Means Wye (Star) Wound Secondary
11 - Is the phase shift between the two windings. The 11 refers to 11 on a clock face, hence 30 degrees.
What is inductance and types of inductance?
inductor is a electronic component that resist a change in the flow of current inductance is that property of inductor.
What happens when secondary of the transformer is open?
The secondary winding leakage inductance limits the current during a short. It seems that the current through the primary is limited by winding resistance and leakage resistance when the secondary is shorted.
What happens to resistance when increasing cable length?
this is because there will be more collisions between atoms and electrons as there is a greater distance to travel. The longer the length of wire, the more collisions. It is like a traffic jam, the longer the road, the loner you are stuck in it for.
Why does the emitter bypass capacitor increase the voltage gain?
In the common emitter configuration, gain is hFe or collector resistance divided by emitter resistance, whichever is less. Placing a capacitor across the emitter resistor effectively makes the emitter resistor less, for higher frequencies, so the gain is higher for higher frequencies. This creates a high pass filter, or a low cut filter, depending on what you want to call it.
Why inductors are not used in active filters?
inductors are more expensive and complex.and they take up space. Their effect can be replicated by active circuits.
Difference between clipper and clamper circuit?
main difference is that clamper circuit contains a caoacitor while clipper not
clipper cut off the specific portion of wave
What happens to the voltage if the current increases?
Yes, if the resistance remains constant. Power is voltage times current, and current is voltage divided by resistance, so power is voltage squared divided by resistance. In essence, the power increases as the square of the voltage.
Why do resistor voltage decrease while capacitor discharges?
The reason why resistor voltage decreases while a capacitor discharges is because the resistor acts like a source of electrical energy. As the capacitor discharges, it draws energy from the resistor, which causes the voltage across the resistor to decrease. This is because the capacitor is acting like a drain, and is taking energy out of the resistor, thus causing the voltage across the resistor to decrease.
The resistor and capacitor work together in order to create a discharge circuit. This is done by connecting the capacitor to the resistor, and then to a voltage source. The voltage source supplies the energy to the resistor, and then the resistor transfers this energy to the capacitor. As the capacitor discharges, it takes energy from the resistor, which causes the voltage across the resistor to decrease.
In order to understand this process better, it is important to understand the basics of Ohm's Law. Ohm's Law states that the voltage across a resistor is equal to the current through the resistor multiplied by the resistance. As the capacitor discharges, it takes energy from the resistor, which means that the current through the resistor decreases, and therefore the voltage across the resistor will also decrease.
What is input and output impedance?
To get all the voltage from a source to a target without loss you need voltage bridging, that is a relative low output impedance to a higher input impedance. Usualy the input impedance is more than ten times higher then the output impedance.
An input impedance is called also a load impedance or an external impedance.
An output impedance is called also a source impedance or an internal impedance.
Do The resistance of a material generally increases as its temperature increases?
The answer to this depends on the material from which the resistance is made.
For most materials resistance increases with increasing temperature. This is referred to as having a "positive temperature coefficient".
Some materials have a negative temperature coefficient; these do have uses in electronics.
Average kilowatt hours a us household uses in a month?
From an article about Al Gore's exorbitant energy consumption, dated February 26, 2007:
"The average household in America consumes 10,656 kilowatt-hours (kWh) per year, according to the Department of Energy."
http://www.tennesseepolicy.org/main/article.php?article_id=367
10,656 / 12 = 888 kWh per month
Why the step down transformers are in delta star?
There is no such thing as a multi phase transformer. A transformer has one phase input and one phase output. There may be multiple windings on input and on output, but they are all in phase, insofar as the power factor allows it.
What we call a three phase transformer is really three transformers operating together, one on each of the three phases. They do not share the phases. They do not share windings. They do not share cores. They do not share magnetic fields. They are independent. They only thing they might share is they same physical container.
Star-delta configuration for three transformers (emphasis on plural) is a common configuration, although star-star is supposed to be better from an eddy current perspective. It comes down to the objectives of the load, and whether or not there there is a neutral involved, and where the neutral is connected. You can still have a neutral in star-delta, but it won't be centered in the middle of the three phase power - it will be centered in the middle of one of the split phase single phases, in the style of 120/240 split phase like typical residential power. Again, it comes down to objectives.
AnswerThree-phase ('polyphase') transformers are widely-used in electricity transmission and distribution systems.
A three-phase transformer typically comprises a common, three-limb, silicon-steel core, around which are placed three pairs of primary- and secondary-windings, entirely enclosed within a sheet-steel tank containing a mineral oil for the purpose of insulation and cooling. For a delta/wye configuration, the primary winding is accessed through three ceramic bushings, while the secondary winding is accessed through four ceramic bushings.
Three, separate but identical, single-phase transformers can also be connected together to create a 'three-phase transformer bank'. Three-phase distribution transformer banks are more common in North America than in the UK, where three-phase transformers are the norm.
Most power transformers (i.e. transformers used in the transmission system) are three-phase transformers, although at really high MV.A levels, three-phase transformer banks are used because their very large physical size makes them easier to transport and install.
In the UK, distribution transformers normally use the delta/wye configuration, because the high-voltage primary is supplied from an 11-kV three-phase, three-wire, system, while the low-voltage secondary supplies a three-phase, four-wire, system with a line voltage of 400 V and a phase voltage of 230 V.
In North America, a three-phase distribution transformer's secondary configuration is normally delta-connected, with one phase centre-tapped in order to supply the standard, split-phase, 240/120 V low-voltage system.
