0
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 ohm's law is not applicable in networks?
Ohm's Law: Volage = Current times Resistance Yes, voltage is proportional to current. That applies in simple circuits as well as to complex circuits such as electrical networks. Your statement that "voltage is inversely proportional to current in electrical circuits" is incorrect. Perhaps you are not considering some critical part of the statement, or you simply heard it wrong.
How do you test chopper transformer?
A chopper transformer is a kind of transformer used in an switching power supply.The primary input voltage of it is a Direct current (D.C) unlike any other ordinary step down transformer which uses an Alternating Current (A.C).Chopper transformer uses a switching transistor to produce a secondary voltage..
Electrical current is a fascinating and powerful tool. It can be both safe and deadly: the emissions from a Tesla coil, while awe inspiring, pass harmlessly around and through humans; yet, ramp up the current enough, and severe effects can occur.
The major factors that affect a person are: the amount of current, measured in amperes or "amps"; the path the current takes through the body (i.e. through the heart); and the length of time the body is exposed as a circuit.
The voltage, environmental moisture, whether the heart is in a beat or not, and the person's health can also affect the severity of the shock. The following list details effects of current. Note that 1000 milliamperes (mA) equates to 1 ampere (A).
1 mA of current causes a bit of a tingling sensation, but can be dangerous under some conditions.
5mA of current results in a slight painless shock. Strong involuntary reactions can cause injuries to the person.
6-16mA results in a painful shock, and the individual is less likely to have control over their muscles.
17-99mA results in extreme pain, respiratory arrest and strong muscular contractions. Death is quite probable at this point.
100mA-2A results in uneven, uncoordinated pumping of the heart. Nerve damage begins here. Death is highly likely.
At more than 2 amperes, the heart stops, internal organs begin to cook, and sever burns occur. Death is quite probable without immediate medical assistance.
See the related links below for further details.
What must be applied to an electric charge to make it flow in a circuit?
There are many complex explanations for current flow in electronics. The answer below describes the basic requirements without including great detail. For a more academic discussion, you are advised to look at relevant sections of text books on electrical and electronic engineering.
In order for electrical current to flow, there must be two things:
1) A voltage (sometimes referred to as a "potential difference"). The voltage can be created by a battery, a generator, a solar cell or a mains voltage outlet.
2) A complete circuit. This must include conductors such as wires that start at the positive terminal of the voltage source and at the far end, return to the negative terminal of the voltage source. Other components such as lamps, resistors and switches can form part of the complete circuit.
We must have a voltage for current to flow because without it, there is no "electrical force" to cause the current to flow.
We need a complete circuit so that the current can flow from the positive of the voltage source, through conductors and return to the negative of the voltage source. Current will flow through any complete circuit. If a switch is part of the circuit, when it is open, no current can flow because the circuit has been broken. When the switch is closed, the circuit is complete and current will flow once again.
Therefore, it is possible to have a voltage without a current (switch open, for example) but it is not possible to have a current without a voltage.
NB: Mains electricity is alternating current. It follows the same principles as the DC examples mentioned above although there is a changing voltage rather than a constant voltage.
What is the difference between radio frequency and audio frequency?
They terms frequency are essentially the same, except radio waves are electromagnetic, and acoustic waves are pressure waves. An audio frequency is a range of frequencies that we can hear, approx up to 20Khz, anything past 20Khz is said to be radio waves
In a parallel circuit is the current is shared between the loops?
The current splits, part of it goes through each of the separate branches, then it gets back together again.
This answer is misleading.
What actually happens is this. Each branch draws a current which is determined by the supply voltage divided by the resistance of that branch. The sum of these branch currents is then drawn from the supply.
So, the current doesn't actually 'split', but is the sum of the individual branch currents.
How do you test a capacitor using a multimeter?
A cheap multimeter can be used to test if a capacitor is burnt out. Connect one lead of the capacitor to one lead from a resistor (about 50k ohms). Set the multimeter to a high "ohms" setting and place the test leads on the remaining cap and resistor leads. The display should begin at 50 KOhms and then get higher and higher until it reads infinity/overload.
A bad capacitor will either start at infinity/overload or start at 50KOhms and stay there. It won't tell you the ferad rating of the capacitor, but it will give a starting point to troubleshoot.
What if two current source connected in series?
Theoretically not allowed and practically not safe or desirable to have two current sources in series or two voltage sources in parallel. In practice, the sources will get hot and catch on fire -- very unwise to even try.
Why only 50 hz frequency is used in India?
It may be one of the following reasons:
- It may In US, the frequency is 60Hz and 110V supply, but in India is about 240V, 50Hz supply. For a particular load say 100kW the current will be 0.416A. But in US the same load will consume about 0.9A. Here the thing is the heat produced in the cable because of the flow of current will be large in US compare to India. Since US is a cold country they can use this level but not in India.
- Moreover, once standardisation is fixed for Indian (50Hz) by British, so its continuing and in America its 60 Hz according to their standardisation.
- Its only because, too low value will create fluctuation in apparatus like Bulb starts blinking(persistence of eye is 15 Hz) and too high value will lead more hysteresis and eddy current losses in many machines.
What is the leakage current of a conductor?
A: Transistor like any diode leaks a very small current. This leakage is specified as Ico tested with the base open. Manufacture specification sheets will have this information for each device that they manufacture.
What is the definition of operating point of diode?
The current you set it to work at. Using for example resistors you can set the voltages and currents at a certain DC level. At that point the transistor will work. It is mostly (but not always) used to put the transistor in its linear region.
How many coils are there in a transformer?
There are normally only one set of primary windings in a transformer. Some may have multiple windings though so that they can cover a wider range of input voltages.
How much ohms resistor is needed to drop 12 volts to 5 volts?
The size of the resistor will depend on the load. Let's look at this a bit to see if we can make sense of it. You want to drop the applied voltage to a device from 12 volts AC to 11 volts AC. That means you want to drop 1/12th of the applied voltage (which is 1 volt) across the resistor so that the remaining 11/12ths of the applied voltage (which is 11 volts) will appear across the load. The only way this is possible is if the resistor has 1/11th of the resistance of the load. Here's some simple math. If you have an 11 ohm load and a 1 ohm resistor in series, you'll have 12 ohms total resistance ('cause they add). If 12 volts is applied, the 1 ohm resistor will drop 1 volt, and the 11 ohm load will drop the other 11 volts. A ratio is set up here in this example, and each ohm of resistance will drop a volt (will "feel" a volt) across it. See how that works? If the resistance of the load is 22 ohms and the resistance of the (series) resistor is 2 ohms, each ohm of resistance will drop 1/2 volt, or, if you prefer, each 2 ohms of resistance will drop 1 volt. The same thing will result, and the load will drop 11 volts and the series resistance will drop 1 volt. That's the math, but that's the way things work. You'll need to know something about the load to select a series resistance to drop 1/12th of the applied voltage (which is 1 volt) so your load can have the 11 volts you want it to have. There is one more bit of news, and it isn't good. If your load is a "dynamic" one, that is, if its resistance changes (it uses more or less power over the time that it is "on"), then a simple series resistor won't allow you to provide a constant 11 volts to that load. What is happening is that the effective resistance of the load in changing over time, and your resistor can't "keep up" with the changes. (The resistor, in point of fact, can't change its resistance at all.) You've got your work cut out for you figuring this one out.
An operational amplifier, which is often called an op-amp, is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output.[1] An op-amp produces an output voltage that is typically millions of times larger than the voltage difference between its input terminals.
Typically the op-amp's very large gain is controlled by negative feedback, which largely determines the magnitude of its output ("closed-loop") voltage gain in amplifier applications, or the transfer function required (in analog computers). Without negative feedback, and perhaps with positive feedback for regeneration, an op-amp essentially acts as a comparator. High input impedance at the input terminals (ideally infinite) and low output impedance at the output terminal(s) (ideally zero) are important typical characteristics.
Op-amps are among the most widely used electronic devices today, being used in a vast array of consumer, industrial, and scientific devices. Many standard IC op-amps cost only a few cents in moderate production volume; however some integrated or hybrid operational amplifiers with special performance specifications may cost over $100 US in small quantities. Op-amps sometimes come in the form of macroscopic components, (see photo) or as integrated circuit cells; patterns that can be reprinted several times on one chip as part of a more complex device.
The op-amp is one type of differential amplifier. Other types of differential amplifier include the fully differential amplifier (similar to the op-amp, but with two outputs), the instrumentation amplifier (usually built from three op-amps), the isolation amplifier (similar to the instrumentation amplifier, but which works fine with common-mode voltages that would destroy an ordinary op-amp), and negative feedback amplifier (usually built from one or more op-amps and a resistive feedback network).
If a semiconductor carrying a current ( I ) is placed in a transverse magnetic field ( B ), an electric field ( E ) is induced in the direction perpendicular to both I & B.This is called hall effect.
for full explanation visit http://www.ecematerials.com/2013/07/hall-effect.html
What happens to the voltage in a series circuit when more loads are added?
A: assuming a infinite current source the current will increase accordingly
Diode is a two terminal semicon. Diode is a Switching device
Why DC current is not used in transformers?
A transformer couples energy from the input winding to the output winding by means of a changing magnetic field. AC current is a changing electric field, which produces changing magnetic fields when put to a wire and so is ideal for a transformer. This fact is why virtually all power distibution is AC. If DC were put to a transformer, once the winding magnetized in a fraction if a second, the current drawn would be so much it would blow the circuit. In other words, you can not use DC on a transformer because the transformer would be blown up by it.
Another Answer
When any current passes through any conductor, invisible Electro-Magnetic fields are produced in the immediate space around the conductor; the strength and distance of these fields are proportional to the amount of current that passed through the conductor. The electric field is in the plane of the conductor while the magnetic field is perpendicular to the conductor. If the current is DC, the fields grow to their maximum and stay there. If the DC source is removed, the fields collapse. If there is enough current passing through the conductor, the fields will expand, break away from the conductor, and continue to propagate through space at the speed of light. This is the principal of a radio and TV station antenna. This propagation is also a direct loss of source energy.
Induction is described as the relative motion of a conductor through a magnetic field. This can either be the magnetic field in motion with a fixed conductor, or a fixed magnetic field with the conductor in motion. Either of these conditions will induce an electric current in the conductor.
Transformers work under the principal of induction. There is a primary coil and a secondary coil in transformers. The core of the transformer can be air, iron powder, or solid iron; among other material configurations. The ratio of the windings from the primary to the secondary determines if the voltage will be stepped up or down in the secondary. If there are twice as many windings in the secondary as are in the primary, the output of the secondary will be twice the voltage and half the current of the primary. If there are twice as many windings in the primary as are in the secondary, the output of the secondary will be half the voltage and twice the current of the primary. This rule does not take into consideration any loss in the field generation due to: counter EMF, impedance, propagation, etc.
Since the transformer relies on the principal of induction, there has to be a relative motion between the magnetic field and the coil. If you apply a DC source to the primary of the transformer while watching the output of the secondary, what you'll see is a spike on the secondary where the magnetic field in the primary expanded, cutting through the secondary coil, but did not contract. This does not constitute the fundamental requirements of sustained induction. The above contributor is correct when saying the primary would draw as much current as the DC source could provide, usually ending in some catastrophic failure. The reason the DC current could run away is there is minimal resistance in the primary coil wire to DC current.
There is, in fact, a form of resistance to an AC source applied to a coil. This is known as impedance and is caused by some of the factors mentioned above, mainly "Counter EMF". Counter EMF is a phenomenon produced because one loop of the winding is lying next to the next loop in the winding; when current is sent through the coil. When the magnetic field in the first loop starts to expand, it does so in a particular direction. The "Right Hand Rule of Thumb" can be applied to this scenario to determine which direction the magnetic field is traveling around the wire. Imagine using your right hand to wrap your fingers around a wire with your thumb pointing in the direction of current flow. Your fingers point in the direction of the magnetic field. When this magnetic field expands through the next loop in the coil, it induces a small amount of current in the opposite direction of the source current, which acts as a dynamic resistance to the main current source. This impedance is why current lags voltage by 90° in an inductive circuit.
This subject is both broad and deep.
How diode can be used as switch?
No, a diode can rectify an AC signal but is not able to amplify an AC signal. Diodes are two layer devices whereas transistors have three. It is this very thin 'base' region in the transistor that gives it the ability to give a voltage or current gain.
What will happen if the voltmeter was inserted in place of an ammeter?
You would load the circuit, and it is likely it would not operate correctly. A volt meter is designed to have a very high resistance between the two probes; an ammeter is designed to have a very low resistance.
For instance, say you have a 120 watt light bulb that runs on 120 volts (you would then draw ~1 amp of current). If you tried to measure this with a meter that has .1 ohm resistance on ammeter setting, and 1,000,000 ohms on volt meter:
Error due to loading:
ammeter: .1 / (120 + .1) = .08%; Current will be .999Amps, power to the light bulb will be 119.9 watts
Volt meter: 1,000,000/ (120 + 1,000,000) = 99.9%; current will be 120micro Amps, power to the light bulb will be 14.4 milliwatts (the light bulb will not appear to be on).
1. Compressor
2.A fan
3.A gas, like freon, which vapourises @ a temp lower than room temp
4.The tubing/Piping
An AC is a heat transfer operation.The gas(in the form of a liquid) travels through the piping and it evaporates very quickly cooling the tube.The fan blows air across the tubes into the room, now to turn back the evaporated gas into a liquid so that it can be evaporated again, it is led into the compressor, the compressor is basically a mechanical component, which squeezes the gas back into liquid so that it can be evaporated again, this happens continously, and during compression, a lot of heat is generated, which is thrown into the outside atmosphere.This is the basic working of any refrigating device.
What is the properties of a P-n junction?
PN junction: putting a P-type material next to N-type material to form the PN junction.
P-type is where you have more "holes"; N-type is where you have more electrons in the material. Initially, when you put them together to form a junction, holes near the junction tends to "move" across to the N-region, while the electrons in the N-region drift across to the p-region to "fill" some holes. This current will quickly stop as the potential barrier is built up by the migrated charges. So in steady state no current flows.
Then now when you put a potential different across the terminals you have two cases:
1. +ve end to P-type, -ve end to N-type: The electric field from the external potential different can easily overcome the small internal field (in the so-called depletion region, created by the initial drifting of charges): usually anything bigger than 0.6V would be enough. The external field then attracts more e- to flow from n-region to p-region and more holes from p-region to n-region and you have a forward biased situation. the diode is ON.
2. +ve end to N-type, -ve end to P-type: in this case the external field pushes e- back to the n-region while more holes into the p-region, as a result you get no current flow. Only the small number of thermally released minority carriers (holes in the n-type region and e- in the p-type region) will be able to cross the junction and form a very small current, but for all practical purposes, this can be ignored.
of course if the reverse biased potential is large enough you get avalanche break down and current flow in the opposite direction. In many cases, except for Zener diodes, you most likely will destroy the diode.
What are the advantages and disadvantages of RC phase shift oscillator?
Advantages: it improves frequency stability.
phase modulation n demodulation is easy as compared to frequency modulation.
