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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 wattmeter measure the active power?
The wattmeter contains two coils one is current coil and other is pressure coil.
the current coil is connected in series with the line and pressure coil is connected across the supply.
so, the disc links with the flux which is the resultant of these two.(resultant means consider the vector resultant), which include phase angle also.
the active power P=VI(cosine of angle between v & I).
there fore the wattmeter measures the active power.
CommentThere is no 'disc' in a wattmeter. Furthermore, the current coil doesn't measure the load current, it measures the in-phase component of the load current.
Why the input impedence of op-Amp is very high?
An ideal amplifier will have a very high input resistance, and low output resistance. This is so it doesn't "load" the input circuitry, and can drive output circuitry.
Say you hooked an op amp up to a microphone that kicked out 100mV unloaded. If you shorted out the microphone, the output would approach 0mV (very low resistance load). If you connected a very high resistance load instead, the output would remain close to 100mV. As the load becomes a smaller resistance/bigger load, the output voltage will decrease until it is no longer useful. This is because the microphone has an internal resistance that remains constant while you're varying the attached load. The voltage drop across the internal resistance will increase as current output increases, causing less of a signal to be delivered to the amplifier.
What is the base voltage in a transformer circuit?
depends on the type of trans former.buck or boost.primary winding a secondary winding
Can an electrical short be caused a phase to a phase?
It could be a phase to phase, ph to neutral or earth fault. In single ph wiring ph to ph exhibits no short ckt fault
AnswerYes, but you have got the terminology wrong. There is no such thing as 'phase-to-phase', the correct term being 'line-to-line'. So you can have a short circuit as a result of a line-to-line fault, a line-to-neutral fault, or a line-to-earth fault.
Is electromagnetic induction useful for agriculture?
Induction is necessary to electrical parts of a tractor engine. This makes it useful for agriculture! The same can be said of other tools and equipment used by the farmer. So "yes" is a correct answer to this question.
But was that the intent of the question? Perhaps the question is meant to discover whether there's value in direct electromagnetic stimulation of plants.
In that case, too, the answer is "yes."
In 2009, a study was documented in which potato tubers were exposed to alternating elecromagnetic fields (resulting in induction) of varying strengths. That study cites numerous earlier similar studies. The results showed a definite positive correlation between the strength of the applied field and the growth of the tubers when planted, as well as the storage life of the tubers. Reference below.
What is the starting salary of an electrical engineer?
The starting salary of an electrical engineer in the United States is approximately $52,990 a year. The highest earning ten percent of electrical engineers make approx. $125,000 a year and median earners of the group make $82,000 a year.
Can you reverse the polarity of AC and DC?
We have the capacity to reverse the polarity of a DC voltage, at least as regards what we apply it to. When we consider a DC motor, like, say, the ones in the little "robot wars" we see on TV, the motors can be run in reverse by reversing the polarity of the applied DC voltage. We normally consider AC as already reversing its polarity. It is, after all, AC, which is alternating current. The current alternates because the voltage alternates. We'll avoid any further discussion of the polarity of AC voltages here and leave it at that.
Answer
The problem, here, is that 'polarity' has several different meanings.
Polarity, in the sense of 'electric charge' cannot really be applied to a voltage (potential difference) although it can be to a potential (although the polarity is relative; it depends on the point of reference).
Polarity, in the sense of 'direction', can be applied to a voltage. For example, is the voltage acting clockwise or counter clockwise around a circuit?
Polarity, in the sense of 'connection', can be applied to a voltage. For example, it's important that the line conductor is connected to the centre terminal of an Edison lamp holder or to one or other of the slots in a receptacle (power socket).
As a battery ages and is used up what will the internal resistance be?
As it ages, its Kirchhoff virtual 'internal resistance' increases. Pictured this way, the practical effect is that the open-circuit voltage of a failing cell still measures good, but the voltage quickly sags when you try to draw any current from it
Will a DC motor actually produce voltage if it is spun in reverse?
It'll produce voltage if you spin it forwards, too. The only difference between a DC motor and a DC generator is what you use it for.
A long time ago, cars had DC generators on them instead of AC alternators. When you replaced a generator, you had to "polarize" it so it would make electricity. You hooked it up to your battery and let it run, as a motor, for a few seconds. Don't try that with an alternator because you'll break it.
If you're looking for a neat little elementary-school science project, you can use little Radio Shack electric motors as generators for things like windmills, water wheels, dynamos turned by bicycle tires...
Actually, yesA motor works by passing current through the conductors of an electromagnet (the rotor or armature) suspended in the magnetic field of a permanent magnet (or another electromagnet). The rotor is the moving part, that is, the part that spins. If instead of energizing the rotor's windings, you turned the rotor by hand, you would indeed induce a current in the rotor's windings. Basically you have created a generator.
Motors work on the basic principle of a current going through a conductor producing a magnetic field around the conductor. If you reverse that you have a magnetic field around a conductor which produces current.
Explain capacitance of bundled conductor line?
Capacitors are formed by placing two conductors near each other. Usually, they are plates separated by an insulating dielectric. The capacitance is a function of the area and closeness of the plates. Bundled conductors have capacitance for the same reason - they are conductors close to each other. Since capacitors work by transferring charge (remember that the equation of a capacitor is dv/dt = i/c) then a signal on one conductor can induce a "copy" of the signal on the other line - usually a faint copy, but a copy nontheless. This induced voltage effect is also known as interference, and must be considered in the final system design.
What has to be interchange in order to reverse the direction of rotation of shunt generator?
the direction of the rotation of dc shunt generator could be changed only by changing the direction of rotation of the prime mover
Operation principle of three phase power supply?
http://en.wikipedia.org/wiki/Three-phase_electric_power
Click on this link from Wikipedia. It gives an excellent description of three phase power.
120v to 16v 10w transformer how do you convert 16vDC to 2vDC to run an LED?
Divide the LEDs current into the voltage and derive a proper current limiting resistor value. 16/0.02=800 ohms. That is for a 20 ma LED.
How do you reduce spike current?
by using capacitor on the line we can reduce spike current or we can use a capacitor bank for the rated line capacity.
Which is better a doctor or a engineering?
Assuming that you are capable of becoming any one of them, you need to figure out which one would make you happier. If more money would make you happier, then "doctor" would be a better choice, under the above assumptions.
What is short circuit ratio of an alternator?
Short circuit ratio is the ratio of field current required for the rated voltage at open circuit to the field current required for the rated armature current at short circuit
How do you calculate active power of 250mva and power factor of 95?
.25 x .95 = .2375 watts = 237.5 milliwatts
Power factor has a maximum value of 1, so I assume you meant .95
CommentOnce again, we have questions that use the wrong symbols for electrical units, leading to confusion.
In 'mva', 'V' and 'A' should both have been capitalised, so it is reasonable to assume that 'M' should have been capitalised, too! So what the questioner probably really means is 'MV.A' (megavolt amperes), not mV.A (millivolt amperes)!
So the answer the writer is probably looking for is 237.5 MW (megawatts).
How should an ammeter be placed in a circuit?
An ammeter should be placed in series, between the element you want to know the current of and the node the element was attached to before.
Does Four 1000 Ohm resistors placed in parallel have a resistance of 250 Ohms?
Yes. The equivalent resistance of resistors in parallel is written as 1/Req=1/R1+1/R2+1/R3+... which, in this case, would be 1/Req=1/1000+1/1000+1/1000+1/1000=0.004. This means that Req=1/0.004=250Ohms.
What is Electricity use difference between 3 phase and 1 phase?
A two-phase a.c. system is an archaic system, in which two phase voltages are generated 90 electrical degrees apart. It has nothing whatsoever to do with the US 'split phase' system that supplies North American homes. A two-phase system can be a four-wire system, or a three-wire system, and was useful because, unlike a single-phase system, it could create naturally rotating magnetic fields in induction motors. It has long been superseded by the three-phase system.
Can a 220 volt motor be converted to 110 volt?
only if it,s a multiple voltage motor, there should be a plate showing the hook up, if,s showing 110v /220v then yes other wise NO,
Power dissipated in an 800 ohm's resistor connected to a 230V supply is?
66W
230/800= 0,2875. 230= 66w
The "full load speed" is the speed at which a motor has been designed to turn - usually measured in RPM (revolutions per minute) - when it is delivering its full rated output power.
What is the formula in finding the reduced size wire if the resistivity is increased?
L1-L0=(RESISTANCE*AREA)/RESISTIVITY
where L1=INIIAL LENGTH
and L2=FINAL LENGTH
