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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
Why the output waveform at summing amplifier is out of phase of 180 with input signal?
Because as the signal voltage increases on the base, the base current increases this causes the collector current to increase, this decreases the voltage drop Vc to ground. As the base voltage decreases the base current decreases causing the Collector current to decrease, increasing the voltage drop Vc to ground.
i think dis ans will clerify d doubts of students...
... in CE config..
as Vo=Vcc-Ic Rc nw as Vcc is const. v cn say Vo is directly proportional 2 (-Ic Rc) so nw when d base voltage is increased Ib will inc. thus, Ic will inc. cuz Ic=beta Ib thus Ic Rc drop increases... as Vo is prop 2 -Ic Rc thus, Vo will decrease...thus d curve for d +ve half cycle in which Ib is increasing drawn in 180 deg phase showing Vo is dec. n vice versa 4 -ve half cycle...
nw in CC...
as d o/p is taken frm emitter... Vo= Ie Re so der's no -ve sign..n for d +ve cycle Ie will incr(dat's leakage current) as der's no-ve sign it'll b in phase wid i/p..hence no phase shift as leakage current doesnt incr. so much thus,d o/p voltage Ie Re doesnt inc much thus, d o/p doesnt amplify much thus dis config knwn as emiter follower...
nw in CB,...
d I/P is appiled at emitter n o/p is taken frm collector... so, 4 d +ve half cycle d Eb junc will b more FB thus causing incr. in Ib n thus, in Ic... so inc. in Ic causes inc. in o/p voltage..n during -ve half cycle d junc will b less FB so o/p voltage will b decreasing..hence der's no phase shift...
for any other help..
cont.-
shrey.dhingra51@gmail.com
What property of a diode enables it to convert ac to dc?
A diode allows electrons to pass only in one direction. During the negative half cycle of an alternating current the diode will not allow electron current to pass. It is like a one way valve. This property of diode enables it to convert AC into pulsated DC
Top ten universities of Pakistan in engineering?
In Pakistan, ranking of universities is determined by the HEC. The ranking list is available at the following website:
http://www.paked.net/higher_education/hec_university_rankings.htm
Why 120 degree phase shift is maintained for 3-phase systems?
There are 360 degrees in a full cycle so 120 is one-third so each of the three phases is equally spaced delivering power evenly to the load.
What are the dimensions of an English electrical plug socket?
In England they use Type G plugs and sockets for their standard household electricity supplies. For more information see the Related Link shown below and also the answer to the Related Question.
What is current density of copper busbar for 4000A?
The current density for a copper busbar will vary as the size of the bar. And no, that's not a trick answer. More information about the application is needed to determine what size the busbar is, since only the ampacity was cited here. There are different specifications (sizes) for busbars, as you know. The deal is that there is usually a "temperature rise" factor that delimits what you're supposed to use. Higher temps mandate bigger bars, which you probably already figured out. The basic busbar size is set on how much heat the busbar will generate when conducting it maximun rated current. But factors regarding the thermal environment in which the unit is operating must be considered. Minimum size for 4000A is probably 1/4 x 10, but some applications will require up to 3/4 x 10 with some allowing something in between. With a specified size bar, you can easily calculate the current density by dividing the current (4000A) by the cross-sectional area. Pick one and go for it.
Does a start capacitor control speed?
No. A starter capacitor is just that....for start up purposes only. It does not control speed....this is done by selecting different phases of the running motor wired individually. Motors that rev up and down are called stepper motors and can be controlled by dedicated operating control boards that constantly monitor amps and load resistance.
What happens to a wire if the current capacity is exceeded?
The wire overheats. In a bad case, a fire can be started.
Note that, sometimes, current capacity is actually more a factor of insulation capacity rather than wire size.
A three-phase motor has a rotating magnetic field inside that is set up by the supply, so the armature always rotates in the correct direction. A single-phase motor can in principle start either way so it has a starting winding supplied through a capacitor to provide a small component of rotating field to get it started the right way. After it has picked up speed the starting winding can be switched out.
Differentiate direct proportion from inverse proportion?
when both increaes its direct proportion and when one increase and othe decreases its inverse proportion.
G-load, or gravitational load, is calculated by measuring the acceleration experienced by an object relative to the acceleration due to gravity (g). It is expressed as a multiple of g, where 1 g equals approximately 9.81 m/s². The formula used is G-load = acceleration experienced / gravitational acceleration. This measurement is commonly used in fields like aviation and automotive engineering to evaluate the forces acting on pilots and passengers during maneuvers.
What are the differences between a coal power plant and a hydroelectric power plant?
Coal is used in furnaces to heat water in a boiler to superheated (above 100 degrees Celsius) temperatures, and this steam is used to drive a turbine which, in turn, drives an alternator.
A hydroelectric plant uses the vertical fall of water to drive a water turbine which drives an alternator.
For capacitors connected in parallel the total capacitance is the sum of all the individual capacitances. The total capacitance of the circuit may by calculated using the formula:
where all capacitances are in the same units.
Why does humans conduct electricity?
humans conduct electricity because your body is made 70% of water. so its the best conductor.
What type of current does an uninterrupted power supply use?
Uninterrupted power supply (UPS) is a stand by battery. Charged with mains power, it is designed to give out DC current should the mains power suddenly goes off, long enough for computers to be shut down properly, so avoiding corruption of data and the computer system. I believe that in some larger commercial/military/Government organisations, an inverter DC to AC is in their larger capacity UPS systems, to continue on AC until the mains power is restored.
Another Answer
A UPS is often used to supply computers, in order to protect their data in the event of a power failure. They consist, essentially, of a battery charger, a rechargeable battery, and an inverter. The main power supply maintains the charge on a battery, via a battery charger, and the battery's output is converted to an a.c. output via an inverter. Voltage values are maintained by internal transformers.
How do star and delta configured three phase induction motors perform differently?
Star Delta starter control wiring ensures that initially the Motor winding is connected in Star and after set timer (few seconds) the winding gets connected in Delta automatically. There three power contactors and timers to make it happen.
Why do wee use network theorems and techniques to solve electrical circuits?
network theorems are nothing but the special cases of KCL and KVL .....applying these for each and every branch in a huge network of multiple branches would be a hideous task so by using network theorems this problem can be removed.
various network theorems are :-
1. mesh analysis
2.nodal analysis
3.thevenin and norton theorems
4.dual networks
5.source transformations
in general these theorems are used for solving any circuit consisting of 5-6 loops ,for much complicated networks there are methods based on graph thoery like cut-set method , tri-sec method etc. these methods are difficult when we apply these in simple network but they serve as a very powerfull tool when we apply these on extremely complicated networks
What is the current of an 415kW 415V three-phase load with cosFI093?
47.18 Amps.
Another Answer
The equation for the total power of a balanced three-phase load is:
P = 1.732 x VL IL x power factor, where the subscript, L, represents line values.
So if we change the subject of the equation, for the line current, we have:
IL = P / (1.732 x VL x power factor)
IL = 32 000 / (1.732 x 440 x 0.89)
IL = 47.18 A
Why is multimeter not used for insulation testing instead of a megger?
No, you cannot use a multimeter in place of a megger.
The megger is used to measure insulation resistance, which could be hundreds of megohms or so. In order to do that, you need a high voltage so as to develop the current needed to sense the resistance. Using an ordinary multimeter would not work as the applied voltage is not high enough, causing the sensed current to be too small to detect.
What is the resistance of a unit used to mersure it?
The conventional unit of electrical resistance is the ohm
What is line interphase transformer?
interference line transformer display digit number in electerical device,such as generator it display amps rate&voltage etc.
What are the types of power factor?
there are 3 types of power factor meter:
1). electrodynamic power factor meter,
2).moving-iron power factor meter and
3). nalder-lipman moving-iron power factor meter.
What are the electricity problems in Pakistan?
Causes Of Shortage Of Electricity In Pakistan
Introduction:
The country may plunge into energy crisis by the year 2007 due to rising electricity demand which enters into double digit figure following increasing sale of electrical and electronic appliances on lease finance, The shortage in electricity production in Pakistan is worsening day by day which is causing long break downs and load shedding as called by government. The crisis started about a year ago when all of sudden the electricity consumption increased to a point where all the electricity producing sources failed to fulfill the demand. Apparently it is a matter of supply and demand. The gap between the demand and supply resulted in routine load shedding.
Causes:
The country is facing a huge electric power crisis today. This crisis appears insurmountable in the near or even long-term future, unless proper understanding and correct implementation is undertaken on priority basis. The demand for electricity in Pakistan during the winter months actually goes down and this winter has not been an exception. The systemic issues such as the failure to build new dams and Gen. Mushraf Government's inability to add even a single megawatt of new power to the grid during 9 years of his rule, it seems that the present crisis is a result of bad management and the lack of foresight. The total installed capacity of WAPDA and KESC totals around 19,500 megawatts. Almost two third of this power comes from thermal power plants (fossil fuels), one third is generated by water and about 2% comes from nuclear power plants.
Throughout the month of December, the electricity consumption in Pakistan hovered around 11,000 MW, down from the peak levels of 17,500 MW seen in summer. This demand was well within the installed capacity of WAPDA & KESC yet they were only generating a meager one third (6500MW) of their maximum capacity during this period leaving a huge gap between supply and demand. There are two main reasons for this:
1. The water flow from all major dams was halted starting mid December to allow the annual cleaning of canals in January. This action effectively took all the hydro power off line.
2. The thermal power plants were working far below their potential due to the lack of money caused by the circular debt between various government agencies reaching a staggering 400 billion Rupees.
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Prof Zahid Ali Mangi
D J Sindh Government Science College
Karachi
