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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
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.
It is 230V single phase and 440V in 3 phase system at 50 Hz.
AnswerIf the single-phase voltage is 230 V, then the three-phase voltage must be 400 V, not 440 V. The line voltage is 1.732 times the phase voltage.
What is the same in a parallel circuit?
Always voltage constant in parallel circuit if you look your house wiring all are in parallel therefore 220 volt present in every house but current is different
Is voltage and current proportional to each other?
Yes, in accordance with Ohms law.
Accross a given resistance, current will increase directly proportional to the increase in Voltage.
Voltage(Volts) = Current (in Amps)x Resistance(in Ohms)
You can transpose the formula to find the unknown, given 2 of the values.
What is the circuit symbol for a bulb?
The symbol for a relay is in two parts, and it's rather difficult and ineffective to describe verbally. Therefore, I added a direct link to an image of the accepted symbol to the "Related Links" section.
What circuit is it when electrical current has two or more paths to follow?
A circuit in which electricity only flows in one path is called a series circuit.
JFET = junction field-effect transistor. The transistor design is to restrict/control the current in the channel by expanding or contracting the depletion region, hence the channel cross-section, with a gate signal. The gate is the junction in JFET, compared with using oxide in an MOSFET.
36.9 volts
Explanation:
A trafo works in ratios, much the same as percentage. Easily calculated in this question .
520 turns and 480 Volts secondary.
We find the Voltage of each turn by dividing Voltage by turns. 480/520=0,9230769231 Volt.
Then multiply this by primary turns of which is 40. 40*0,9230769231
=36,9230769231 Volts.
More related info:
This is the AC voltage. In order to find a quite accurate estimate for a rectified DC output with a charging capacitor, simply multiply the AC voltage by 1.44
What converts an alternating current to diredt current?
Alternating Current can be converted to Direct Current by using a DC Converter which contain a Bridge Circuit , a Capacitor and if needed a Transformer.
CommentA 'DC converter' is normally called a rectifier.
The mathematical relationship between current voltage and resistance is known as?
Ohm's Law
AnswerIt's not known as anything; it's simply an equation. Ohm's Law describes constant proportionality between current and voltage for certain, but not all, materials (linear or ohmic) -it has nothing to do with this equation.
What is the difference between analogue and digital system?
the main difference in analoge and digital system is analog is continues type of data and ditital is discreate type of data. e.g old galvanometer having needle is analog but new multimeter is digital in which voltage and current is shown in digits... analog is not much accurate..but digital is accurate...
