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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
What are the applications of rectifiers in use?
A bridge rectifier, is a group of rectifiers (4 in a single phase) wired so that each half of an AC current is passed to respective positive and negative lines of a DC output.
It provides full wave rectification of AC into DC.
How do you reduce 9V DC to 3V DC?
by using the step down transformer we can easily reduce the voltage.if we step down means the current(amps) icrease its vry useful for us
AnswerAs transformers are a.c. machines, you cannot use a transformer for this purpose. You will need to create a voltage dividercircuit -essentially a pair of resistors, of appropriate value, connected in series across the supply.
Reactive power is an odd topic in AC (Alternating Current) power systems, and it's usually explained with vector mathematics or phase-shift sinewave graphs. However, a non-math verbal explanation is possible.
Note that Reactive power only becomes important when an "electrical load" or a home appliance contains coils or capacitors. If the electrical load behaves purely as a resistor, (such as a heater or incandescent bulb for example,) then the device consumes "real power" only. Reactive power and "power factor" can be ignored, and it can be analysed using an AC version of Ohm's law.
Reactive power is simply this: when a coil or capacitor is connected to an AC power supply, the coil or capacitor stores electrical energy during one-fourth of an AC cycle. But then during the next quarter-cycle, the coil or capacitor dumps all the stored energy back into the distant AC power supply. Ideal coils and capacitors consume no electrical energy, yet they create a significant electric current. This is very different from a resistor which genuinely consumes electrical energy, and where the electrical energy flows continously in one direction; moving from source to load.
In other words, if your electrical appliance contains inductance or capacitance, then electrical energy will periodically return to the power plant, and it will flow back and forth across the power lines. This leads to an extra current in the power lines, a current which heats the power lines, but which isn't used to provide energy to the appliance. The coil or capacitor causes electrical energy to begin "sloshing" back and forth between the appliance and the distant AC generator. Electric companies must install heavier wires to tolerate the excess current, and they will charge extra for this "unused" energy.
This undesired "energy sloshing" effect can be eliminated. If an electrical load contains both a coil and capacitor, and if their resonant frequency is adjusted to exactly 60Hz, then the coil and capacitor like magic will begin to behave like a pure resistor. The "energy sloshing" still occurs, but now it's all happening between the coil and capacitor, and not in the AC power lines. So, if your appliance contains a large coil induction motor, you can make the motor behave as a pure resistor, and reduce the current in the power lines by connecting the right value of capacitance across the motor coil.
Why is reactive power so confusing? Well, the math is daunting if not entirely obscure. And the concept of "imaginary power" puts many people off. But this is not the only problem. Unfortunately most of us are taught in grade school that an electric current is a flow of energy, and that energy flows back and forth in AC power lines. This is completely wrong. In fact the energy flows constantly forward, going from source to load. It's only the charges of the metal wires which flow back and forth.
Imagine that we connect a battery to a light bulb. Electric charges already present inside the wires will begin to flow in the circle, and then electrical energy moves almost instantly to the light bulb. The charge flow is circular like a belt, but the energy flow is one-way. Now imagine that we suddenly reverse the connections to the battery. The voltage and current will reverse... but the energy still flows in the same direction as before. It still goes from battery to bulb. If we keep reversing the battery connections over and over, we'd have an AC system. So, in an AC system, only the voltage and current are "alternating," while the electrical energy flows one-way, going from source to load. Where AC resistive loads are concerned, electrical energy does not "alternate." To understand energy flow in AC systems, it's critically important that we understand the difference between charge flow (current, amperes) and energy flow (power, watts.)
What is imaginary power? Simple: it's the unused power which flows backwards and forwards in the power lines, going back and forth between the load's coil or capacitor and the distant AC generator. If your appliance was a pure capacitor or inductor, then it would consume no electrical energy at all, but instead all the flowing energy would take the form of "sloshing energy," and we'd call it "imaginary power." Of course it's not actually imaginary. Instead it's reflected by the load.
What is real power? Even more simple: it's the energy flow which goes continuously from the AC generator and into the appliance, without any of it returning back to the distant generator.
Finally, what is "apparent" power? It's just the combination of the above two ideas: it is the continous-forward-moving or "real" energy flow, combined with the sloshing or "imaginary" energy flow.
What can electrical shock cause to you?
we do get electric shocks as when we hold a peice of electric wire in our hands and when the electricity switched on, the electrons get transferred through us in the free air. if we hold a peice of cutted wire in both our hands (one hand holding one hand and the other holding another end ) and we complete the circuit and switch the electricity on, nothing will happen but at the point where we leave the wire from our hands, we will get n electric shock.
Difference between a diode and a transistor?
diode is a bipolar device and transister is a three terminal device
a diode will conduct any time there is a positive voltage from cathode[-] to anode[+] following an exponetial curve of the diode.
a transistor can control the same exponential curves by a voltage applied to the base.
Why tungsten filament does not obey ohm's law?
A tungsten filament does follow Ohm's Law at any instant of time. You may be confused in that the filament resistance changes from its "cold" state to its "hot" state. When cold the resistance is about 1/15 the resistance of what it is when the filament heats up, which happens very quickly. At any instant Ohm's Law holds. When the voltage is applied you have an initial current draw that exceeds the steady state current draw based on the change in resistance.
AnswerOhm's Law either applies, or it does not. It cannot apply 'at an instant of time' -a change in current is either proportional to a change in voltage, or it isn't!
A tungsten filament does not obey Ohm's Law, because the current flowing through the filament does not increase in proportion to the applied voltage. This is because the resistance changes due to the filament's increasing temperature as the applied voltage increases. This is why Ohm's Law specifies that current is proportional to voltage, provided the temperature remains constant.
Although tungsten doesn't obey Ohm's Law, the so-called Ohm's Law equation applies whether a circuit obeys Ohm's Law or not. This is because the formula is really derived from the definition of the ohm, and not from Ohm's Law itself, which makes absolutely NO reference to resistance!
How do you find the branch current in parallel circuit?
For each individual branch, you can use Ohm's Law - just divide the voltage by the resistance.
A current flowing towards the viewer in a cross section conductor is shown by?
Sketch the direction line of force around a conductor which is carrying current away from the viewer and also towards the viewer.
How do you convert 380v 3 phase to 220v 3 phase?
Mathematically, just divide 480 by the square root of three.
Electrically, 480V refers to the line-to-line value of a three phase system. For example, measure the voltage across A-phase and B-phase and you'll get 480V. 277V is the line-to-neutral value. Measure the voltage across A-phase and the neutral conductor and you should get 277V.
How is total capacitive reactance for parallel capacitors using their reactances is calculated?
Total capacitance for parallel capacitors is simply the sum of all capacitor's individual capacitances. This would apply within (reasonably) any frequency, ignoring non-ideal resistance and inductance, so the same can be said for capacitive reactance.
What is the advantages of mosfet?
Advantages:-
1- mosfet are small compare to bjt's so it fabricated easily and space saving scheme on the ic's
2- mosfet's input impedance are very high so they do not load the circuits. loading effect doesn't arise.
3- operating frequency is very high so may be used at higher frequencies.
4- used in digital circuits for it's reliability.
5- effect of noise is less than bjt. so high signal to noise ratio.
6-mosfets are unipolar devices so reverse saturation current doesn't exist.
7- it consume less D.C power rather than BJT.
Disadvantages:-
handling is not easy-
Mosfet is very sensitive to electrostatic charge so it may be destroy when you touch the pins of a mosfet devices by hand.
trans conductance is low than BJT.
What is an example of Ohms Law?
The simplest example of Ohm's Law is an old fashioned dimmer switch in your house. As you turn the dimmer switch up, the light gradually brightens until it reaches full intensity. Conversely, you can turn the dimmer switch down, and the light gradually darkens.
The dimmer switch is a variable resistor. That is, the electrical resistance of the dimmer switch changes as you rotate the knob. Ohm's Law tells us that the flow of current is directly proportional to the voltage, and inversely proportional to the resistance. Since the voltage across the switch doesn't change, the only thing that changes is the resistance when you turn the dimmer switch knob.
As you turn the dimmer switch down, you are actually increasing the resistance of the dimmer switch. The current is inversely proportional to the resistance, so as the resistance goes up, the current (flow of electricity) goes down, and the light gets darker. This is an example of Ohm's Law.
NOTE: This example applies to rheostat switches, and does not apply to modern current-clipping dimmer switches. Rheostat switches are seldom used now because they can overheat, but the illustration is still a useful example of Ohm's Law.
A capacitor in its simplest form is merely two electrically conductive plates separated by an insulator from each other. As such the capacitor will block any DC voltage from passing through it, up to the electrical dielectric strength of the insulator. The capacitor will accept a DC charge and an electrical field will exist between the plates of the capacitor. The capacitor will retain this charge until it either leaks away via the high electrical resistance of the insulator, or is intentionally discharged.
When an AC or varying voltage is applied to a capacitor, a varying electrical field is set up between the plates of the capacitor. This will thus pass through the capacitor, and can be seen on the opposite plate. Thus, a capacitor will pass an AC voltage.
Now,as to the question, " application of Capacitor". One of the oldest and most useful of capacitor applications is filtering or smoothing the output of an AC to DC power supply. In this supply, an AC voltage is rectified by a diode into a varying DC voltage. A capacitor is placed across the output, and serves to supply voltage or "fill in" the output whenever the output voltage is less than the capacitor. The capacitor subsequently recharges on the next cycle and repeats the process. Thus, the output voltage of the power supply is smoothed out.
What is a current in a circuit measured in?
amps
AnswerElectric current is measured by means of an ammeter. Electric current is expressed in amperes (symbol: A), which is defined in terms of the magnetic effect of an electric current -i.e. the force between two, parallel, current-carrying conductors.
If you take a permanent magnet and heat it up past the Curie temperature (or Curie point, Tc) and cool it, the magnetic domains in the magnet, which were aligned when it was made, will become randomly oriented. When the "magnet" cools, its magnetic properties will have "disappeared" and the you'll have a piece of metal alloy. If you like, you can make a new magnet out of your hunk of metal by heating the metal past the Curie point again, applying a static magnetic field to it, and then cooling it back down in the presence of the magnetic field. That's the way the magnet was manufactured and made into a magnet to begin with.
Why does the voltmeter input have a much higher resistance than the current input?
Anything that a voltmeter is measuring has some internal output impedance. If the voltmeter had a low input impedance, these two impedances would form a voltage divider and reduce the voltage measured.
The voltmeter has a high input impedance so that it does not affect ("load down") the thing it is measuring.
What is the main advantage of an fet transistor over a bjt transistor?
BJT & FET parameters are temperature dependent. In BJT the collector junction resistance decreasing ( collector current increasing) with temperature raise.Due to the highe temperature & current transistor will damage quickly. In FET drain resistance increasing (drain current decreasing ) with increasing temperature.Due to this property it will not damage easily. We can say from the above two statements FET is more temperature stable.FET can use in highe temperature applications.
What are the disadvantages of TTL?
The disadvantages of TTL are as follows:
- High power consumption
- It functions just on 5v
- The fan-out capacity for this device is low
- Low input resistance
What are normally open and close circuits?
The electric path which starts from the positive terminal of a cell or battery ends at its negative terminal, without any break, is called closed electric circuit or complete electric circuit. The electric path,which starts from the positive terminal of a cell or battery, is broken at some point, is called open electric circuit or incomplete electric circuit.
What is a material that has a high resistance?
Diamond, rubber, plastic, styrofoam, ice, wood, glass, paper, concrete.
How voltage gets converted into current in an ammeter?
A: It must be be understood that current needs voltage other wise it is zero. An ammeter for DC is always a voltmeter that reads small IR drop to convert that reading into current present. Like an ohmmeter needs volts to read ohm. Both reading are volts it just convert those reading into whatever scale is switch to.
How does a zener diode work in reverse bias?
Zener diodes operate like any other diode in reverse bias, they just have the point where they breakdown more carefully controlled, and usually lower than the typical ~50V for a standard silicon diode. The process by which most diodes (with breakdowns larger than a few volts) operate under reverse biases strong enough to cause breakdown is called "Avalanching".
Avalanching is where the reverse biasing is strong enough that the electric field between the positive and negative terminals grows to a point where the electrons and holes being swept across the junction have enough energy so that when they eventually release that energy it is enough to generate a new electron and hole pair which themselves are swept away by the electric field also.
What is a disadvantage of using a parallel circuit?
While a parallel conversion minimizes the risk of major flaws in the new system causing irreparable harm to the business; it also means the cost of running two systems over the period must be incurred. Because running two editions of the same system on the computer could place an unreasonable demand on computing resources, this may be possible only if the old system is largely manual
What are the properties of a semiconductor?
There are a few (general) properties of semiconductors:
- Allowing current to move more easily in one direction than another
- Operating better at high temperature (as opposed to normal conductors where the reverse is true)
- The can exhibit variable resistance
- They can be sensitive to light
- They can be sensitive to heat
- Can used to produce coherent light (semiconductor lasers)
The exact property is determined by the make up of the semi-conductor
The basic element of a semiconductor memory is the memory cell. Although a variety of electronic technologies are used, all semiconductor memory cells share certain properties:
- They exhibit two stable (or semi-stable) states, which can be used to represent binary 1 and 0.
- They are capable of being written into (at least once), to set the state.
- They are capable of being read to sense the state.
What does voltage current mean?
V=IR, voltage is directly propostional to current and resistance (by ohm's law).
CommentVoltage is not 'proportional to resistance'. Resistance is a constant, and is not affected by voltage at all.
