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Electronics Engineering
Electronics Engineering is a branch of engineering that deals with practical applications of electronic components, devices, systems, or equipment. Electronics are devices that operate on low voltage sources, as in electron tubes, transistors, integrated circuits, and printed circuit boards and use electricity as part of its driving force.
24,372 Questions
What is a flip-flop in digital electronics?
Yes, a flip flop is a type of electronic logic circut. It is a bistable device, capable of being in one state or the other, "remembering" that state, until some signal triggers it to change state.
A flip flop is also a type of foot wear, but this was an electronics question. :-)>
there are many uses.
one major use i remember is in rectification i.e convert ac to dc
For switch operation
What is parasitic inductance of capacitor?
A: PARASITIC means like a parasite is there to offset the actual circuitry it can be inductance and/or capacitance A capacitor is usually wound in a coil this coil if frequency is hi enough will behave as a small coil has been added to the circuit. Hi frequency PWM capacitors have indeed four lead to reduce not eliminate this inductance
What is the colour code on resistors?
A: The basic color code for value is as follow 0 black, 1 brown 2 red 3 orange 4 yellow 5 green 6 blue 7 violet 8 grey 9 white if i remember correctly. To read the value is simple 153 for example means 14 and the last number is the multiplier in this case 3 zeros translated as 15000 or 15k resistor. There maybe a fourth band for % +/-
A sentence used to memorize this is "Bad boys rape our young girls but violet gives willingly to gold orange or 20%.
What are the differences between monostable and bistable multivibrators?
The bistable multivibrator, or flip-flop, will stay in one or the other state indefinitely, until it is told to change state.
The monostable (or astable) multivibrator, or one-shot flip-flip, will stay in one state indefinitely, but once set to the other (triggered) state, it will remain there for only a certain time. There are two varieties. The non-retriggerable one-shot will generate a pulse of known width when triggered, and will complete its cycle no matter what the input does. The retriggerable one-shot will generate a pulse of variable width, minimum being the base time constant, and the pulse can be extended (retriggered) as desired.
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.
Can a 1250 mAh battery replace a 1100 mAh battery?
Yes, provided all other factors are the same (shape, size & voltage rating). The rating mAh stands for "milli Ampere hours" and is a measure of electrical storage capacity. The 1250 mAh will last a little longer when fully charged.
Is there anyway to get 120V 60hz from a 240V 50hz power supply?
The following answer maybe more in tune with the question. In North America our domastic single power supplies are 110/220/60hz or 120/240/60hz or 120/208/60hz etc. In simple terms to explain the way to generate these power supplies are to connect two generators or generator windings in series (3 wire system, lets give them a color code of Black-White-Red)(White=centre tap or neutral wire) with output of 110 volt obtain from Black with White or Red with White and 220 volt from Black with Red. While in Europe the power supply is 220v/50hz generated with one generator with no tap for 110v/50hz. ?Answer The motor-generator method is the traditional method, but for the last 30 or 40 years, and electronic method would usually be preferred. Frequency changing is much more complicated than voltage changing, but it can be done, even up to gigawatt levels. A rectifier first converts the power to DC, and an inverter then produces the required output frequency and voltage. The first answer gave an example of this approach.
Can a radio receiver be located with a detector?
Yes, a radio receiver can be located with another receiver or tracer, most radio receivers is of the regenerative type and it has a local oscillator that is used to generate an intermediate (IF) signal of 465Khz on shortwave and 10.7Mhz on the higher frequencies like a FM or TV receiver, that oscillator is like a low power transmitter that is transmitting an un-modulated RF signal.
Any nearby receiver can pick up this signal although no sound will be heard on the receiver, to be able to hear a signal the tracer is equipped with a BFO, (Beat Frequency Oscillator) that will generate an audible tone when a signal is received, the same way as the local oscillator generate the IF signal but only in the audible frequencies and a signal strength meter, then with a directional antenna, the receiver that is to be traced can be pin pointed.
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).
How is the transmitter of a cellular telephone different from a powerful radio transmitter?
A radio plays music, and is not a phone. A telephone is used for talking between two persons.
How was the first radar invented?
To detect "the presence of distant metallic objects". (Taken from the Wikipedia page on Radar). You can read more about its beginning in the history section of it.
http://en.wikipedia.org/wiki/Radar#History
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
Which term refers to the number of electrons that move through a conductor in one second?
That description doesn't fit any electrical term, probably because it's not useful.
The number of electrons passing a single point in the conductor in one second
is proportional to the electrical current, and is described in units of amperes.
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
Relationship between the frequency of the overtones and the and the fundamental frequency?
Fundamental frequency = 1st harmonic.
2nd harmonic = 1st overtone.
3rd harmonic = 2nd overtone.
4th harmonic = 3rd overtone.
5th harmonic = 4th overtone.
6th harmonic = 5th overtone.
Look at the link: "Calculations of Harmonics from Fundamental Frequency".
Where did the electrons from cathode ray come from?
In a cathode ray tube (CRT), the particles, which are electrons, originate at the heated cathode, becoming the so-called cathode rays. The electrons stream off the cathode and rush over to the anode.
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.
Can you match a 6 ohms impedance amplifiers with 4 ohms speakers?
There is really no 3 ohms amplifier on the market with an output impedance of three ohms for power matching. You will find there 0.3 ohm or less for voltage bridging. Scroll down to related links and look at "Interconnection of two audio units - Power amplifier and passive loudspeaker".
How do cell phone jammers work?
How Cell Phone Jammers work
Cell phones are everywhere these days. According to the Cellular Telecommunications and Internet Association, almost 195 million people in the United States had cell-phone service in October 2005. And cell phones are even more ubiquitous in Europe.
It's great to be able to call anyone at anytime. Unfortunately, restaurants, movie theaters, concerts, shopping malls and churches all suffer from the spread of cell phones because not all cell-phone users know when to stop talking. Who hasn't seethed through one side of a conversation about an incredibly personal situation as the talker shares intimate details with his friend as well as everyone else in the area?
While most of us just grumble and move on, some people are actually going to extremes to retaliate. Cell phones are basically handheld two-way radios. And like any radio, the signal can be disrupted, or jammed.
In this article, you'll see how cell-phone jammers work and learn about the legality of their use.
Disrupting a cell phone is the same as jamming any other type of radio communication. A cell phone works by communicating with its service network through a cell tower or base station. Cell towers divide a city into small areas, or cells. As a cell-phone user drives down the street, the signal is handed from tower to tower.
A jamming device transmits on the same radio frequencies as the cell phone, disrupting the communication between the phone and the cell-phone base station in the tower.
It's a called a denial-of-service attack. The jammer denies service of the radio spectrum to the cell-phone users within range of the jamming device.
amming devices overpower the cell phone by transmitting a signal on the same frequency and at a high enough power that the two signals collide and cancel each other out. Cell phones are designed to add power if they experience low-level interference, so the jammer must recognize and match the power increase from the phone.
Cell phones are full-duplex devices, which means they use two separate frequencies, one for talking and one for listening simultaneously. Some jammers block only one of the frequencies used by cell phones, which has the effect of blocking both. The phone is tricked into thinking there is no service because it can receive only one of the frequencies.
Less complex devices block only one group of frequencies, while sophisticated jammers can block several types of networks at once to head off dual-mode or tri-mode phones that automatically switch among different network types to find an open signal. Some of the high-end devices block all frequencies at once, and others can be tuned to specific frequencies.
To jam a cell phone, all you need is a device that broadcasts on the correct frequencies. Although different cellular systems process signals differently, all cell-phone networks use radio signals that can be interrupted. GSM, used in digital cellular and PCS-based systems, operates in the 900-MHz and 1800-MHz bands in Europe and Asia and in the 1900-MHz (sometimes referred to as 1.9-GHz) band in the United States. Jammers can broadcast on any frequency and are effective against AMPS, CDMA, TDMA, GSM, PCS, DCS, iDEN and Nextel systems. Old-fashioned analog cell phones and today's digital devices are equally susceptible to jamming.
The actual range of the jammer depends on its power and the local environment, which may include hills or walls of a building that block the jamming signal. Low-powered jammers block calls in a range of about 30 feet (9 m). Higher-powered units create a cell-free zone as large as a football field. Units used by law enforcement can shut down service up to 1 mile (1.6 km) from the device.
Electronically speaking, cell-phone jammers are very basic devices. The simplest just have an on/off switch and a light that indicates it's on. More complex devices have switches to activate jamming at different frequencies. Components of a jammer include:
Antenna
Every jamming device has an antenna to send the signal. Some are contained within an electrical cabinet. On stronger devices, antennas are external to provide longer range and may be tuned for individual frequencies.
Circuitry
The main electronic components of a jammer are:
* Voltage-controlled oscillator - Generates the radio signal that will interfere with the cell phone signal
* Tuning circuit - Controls the frequency at which the jammer broadcasts its signal by sending a particular voltage to the oscillator
* Noise generator - Produces random electronic output in a specified frequency range to jam the cell-phone network signal (part of the tuning circuit)
* RF amplification (gain stage) - Boosts the power of the radio frequency output to high enough levels to jam a signal
Power supply
Smaller cell phone jammers are battery operated. Some look like cell phone and use cell-phone batteries. Stronger devices can be plugged into a standard outlet or wired into a vehicle's electrical system.
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.
