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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 meant by saying at what current is transistor biased?
The saying "at what current is transistor biased" means to ask the current through the transistor when there is no signal present. Typically, a transistor is biased at the center of its linear region, so as to minimize distortion. This, of course, depends on whether or not the transistor is AC or DC coupled, and where the clipping points might be.
Why do voltage have very high resistance?
Voltage and resistance are distinctly different quantities. I can say some voltages have very low resistances (and high currents), such as when you drop a hair dryer into the tub. You're question as it is written does not make sense.
How do you measure the power input and power output for the step-up transformer?
Power input to a transformer = (voltage across the primary winding) x (current through the primary)
Power output = (voltage across the secondary winding) x (current through the secondary)
It doesn't matter whether the transformer is used in step-up, step-down or simple isolation.
What is meant by hysteresis voltage in schmitt trigger?
A schmitt trigger is a type of dual threshold voltage comparator, with the difference between the two thresholds being the hysteresis voltage. Only one of the two input thresholds is active at a time and it is controlled by the present binary state of the output of the schmitt trigger, making the circuit bistable. This allows the schmitt trigger to ignore small variations and/or noise in its larger input signal that would cause false outputs (glitches) in an ordinary single threshold voltage comparator as the input signal is crossing the threshold.
Many digital logic ICs that are intended for use in noisy environments have schmitt trigger circuits built in on some or all of their inputs to increase their noise immunity. Schmitt triggers are also used in many analog sensing devices that produce digital outputs as a means of "filtering" spurious input signals from the real input signal.
Any gap in a series circuit causes the whole thing to stop working. That is why houses are wired in parallel with each other, and indeed there are many parallel circuits inside each house.
How do you get rid of unwanted eddy currents?
To eliminate eddy currents you can cut small slits in metals. This will prevent larger eddy currents from occurring. Placing insulators between small laminations can also help to protect against eddy currents.
What is the difference between Dbi and Dbm?
There are a few terms that need to be understood. [dBm,dBd,dBi and dB] For antennas, a common reference unit is the dBi, which states the gain of an antenna as referenced to an ISOTROPIC source. An Isotropic source is the perfect omnidirectional radiator, a true "Point Source", and does not exist in nature. Consider it a source which is the center of the sphere and the energy is coming equally out of it as a sphere. Now in reality nothing like that exists. It's also 2.41 dB BIGGER than the next common unit of antenna gain, the dBd, When you convert that to a real antenna.
So a simple dipole antenna has a gain of 2.41dBi, and a gain of 0dBd, since we're comparing it to itself.
Now lets talk about dBm, dBm is not is reference to anything else but the used as an actual gain ( say amplifiers ) , P(dBm)=10*LOG(1000*Power in milliwatts,10), an amp with an output of 30dBm puts out 1 Watt. It is not in refernce to two power level but directly correlating the gain of a device.
Now when you talk about a dB it is a relative measure of two different power levels. 10log (p1/p2, 10).
Why do you need a carrier wave?
In radio transmission, you could theoretically transmit radio signals at audio frequencies.
However, because the wavelength of electromagnetism at audio-like frequencies is Huge and the frequency of a radio transmitter dictates the size of the antenna and the power requirement, you would need A Very Big Antenna and a Very Big Power Supply to do this. So, we've learned to transmit at higher "carrier" frequencies, modulating either the amplitude or frequency of the carrier signal with our audio and subtracting the carrier at the receiver end.
Is soil a good conductor of electricity?
That depends on your soil and your definition of "good".
Dry soil is probably a very poor conductor.
Wet soil can be a pretty good conductor if you have large contact surface areas and dissolved salts in the water.
Why current leads in capaciter?
Capacitors resist a change in voltage. It takes current to effect a voltage change, resulting in the current "leading" the voltage. Similarly, inductors resist a change in current. It takes voltage to effect a current change, resulting in the current "lagging" the voltage.
What does forced commutation mean?
The term "Forced commutation" is used when a thyristor is turned off using external components.
If a thyristor is used in a DC circuit, when first turned on, it will stay on until the current goes to zero. To turn off the thyristor it is possible to use a Forced commutation circuit. The circuit creates a reverse voltage over the thyristor (and a small reverse current) for a short time, but long enough to turn off the thyristor.
A simple circuit consist of a precharged capacitor and a switch (e.g. another thyristor) parallel to the thyristor. When the switch is closed, the current is supplied by the capacitor for a short while. This cause a reversed voltage over the thyristor, and the thyristor is turned off.
How do I test a capacitor when I cannot remove it out of circuit?
You cannot. It must be taken out of the circuit and then tested on its own.
That's not 100% true because, if it has wires at its ends, you can cut through one wire with an appropriate tool and then test the capacitor "out of circuit". If the capacitor is ok you can then re-join the two cut wire ends by applying a blob of solder carefully. (But, to avoid damaging the capacitor, use a suitable heat sink to shield the body of the capacitor from the heat of the soldering iron.)
With direct current a capacitor also works like a special type of resistance. Whilst being charged up, it will show low resistance. As it slowly (or quickly) charges, the resistance will grow larger and larger. Whenever I repair circuitry and I have doubts about a capacitor (in the uF area) I simply use my multimeter on its Ohms setting. If a capacitor has shorted, then the result will be 0 Ohm. If the capacitor is working, or partially working, the resistance will gradually increase until it is out of range of the multimeter.
Use an ohm-meter first to test the on-board capacitor and then use it to test a similar capacitor off-board, to see if the results sort of match up.
Most often they will not match completely as on-board you also measure the effect of all other components connected into circuit with the capacitor. It might point you in the right direction though.
On a separate thought, if you really cannot remove it, or disconnect one of its connections, then why test it at all? If it really can't be removed to replace it, then it makes no sense to test it!
A capacitor can be tested using multimeter without removing it from circuit. but in order to check it, its polarities should be noted and then keep the positive terminal of multimeter on positive of capacitor and negative terminal on negative. It is vital to note that the readings will be affected by the remainder of the circuit. To test for capacitor function in circuit demands a good understanding of the circuit operation.
Of course there are ways to test capacitors, both in circuit and out. While a truly accurate test involved taking the cap out of circuit, a basic test can certainly be done in circuit.
Out of circuit, one can either connect to a VM, or better yet, an oscilloscope, and measure the time for voltage to decay to zero across the capacitor. This time should equal the time given by the equation for the time constant, and is dependant on the values associated with that particular capacitor.
For RC circuits, this equation equals:
τ = R × C. It is the time required to charge the capacitor, through the resistor, to 63.2 (≈ 63) percent of full charge; or to discharge it to 36.8 (≈ 37) percent of its initial voltage. These values are derived from 1 − e − 1 and e − 1 respectively.
It is important to keep in mind that one must apply a voltage across the capacitor at its rated value. Thus, if it is a 400V capacitor driving a tube amp, for instance, it must be driven at around 400V. Driving it at 12V will lead to useless results.
The only proper way to check for a capacitor value and or leakage is with a proper test bridge: set it to the capacitor's DC rating with it removed from the circuit completely. Any other way is just waste of time.
Additionally, a common in-circuit test for a electrolytic capacitor is to measure its Equivalent Series Resistance (ESR) which can be done with an ESR meter. This is a quick and easy way to locate failing electrolytic capacitors, especially in power supply circuits.
An effective method of testing any component in-circuit is with an in-circuit curve tracer. If you have an oscilloscope with X-Y input mode you can easily build one of these on your own. They do take some getting used to before you can use it effectively and are most useful for good board vs. bad boardcomparison.
What size resistor is needed to allow a 220 volt coil in a relay operate on 277 volts?
You will need to know the amount of current flowing through the coil when 220 volts is applied across it. A resistor in series with the coil will limit the current so that the coil only sees 220 volts. The resistor will need to drop 57 volts. So, 57 volts divided by the current in amps will give you your required resistance. You will need a resistor with a high power dissipation rating with 57 volts across it. Your resistor will probaly need to dissipate several watts. For example: A 220 volt coil with 300 milliamps (.3 amps) will require a resistor of 733 ohms. The power dissipation of the resistor would need to be 17.1 Watts! You might try using a light bulb as a series resistor. Ensure that it can handle 57 volts. To complicate matters, is that AC or DC you are using? AC relays have inductance build in, in order to increase the specific "ac resistance", thus the same coil could use as little as 0,001A so you will need a very low value resistor. Anyway, if any 220V relay uses as much as 300mA, I doubt if you will be able to pick it up with one hand! Such a relay coil will draw about 66W of power! I have a 16A rated contact 230V relay. Its current is 0,0015A that is equivelant to 0.33W at 220V!
There are a number of components in any circuit and their job is to restrict the flow of electrons and reduce the current or voltage flowing by converting electrical energy to heat. In other terms, electronics control the electrical circuit. Electric charge is nothing but the flow of electrons from one object to another. The working of the microwave is the example of how electronics work. In a microwave, electricity provides the power that generates high-energy waves that cook your food and electronics controls the electrical circuit that does the cooking.
Most motion detectors work on the principle of the Doppler effect. It's applied to the transmission of an ultrasonic signal and the comparison of the return or echo to what was transmitted. Any difference is caused by Doppler effect. Something was moving toward or away from the transmitter of the detector, and this caused an "apparent" change in the frequency of the echo. And that will set off the alarm. Use the link to the related question (which you will find below) to learn more about the Doppler effect.
Motion detectors used with security systems are passive infra-red (PIR) motion detectors, sensing both motion and heat to detect an intruder. They have a photo-diode that is sensitive to the heat radiation frequencies of the human body, and a special lens that looks at 20 - 30 narrow fields within the protected space. They 'see' the temperature of the background, and any change to this temperature is considered to be a suitable trigger. A person (or animal) moving in the space will move in and out of the fields of view, giving infra-red images to the detector in a 'now you see me, now you don't' pattern.
This generates a series of pulses as the target moves into and out of the fields of view of the PIR lens system. Even if part of your body is at the same temperature as the background, other parts will be at different temperatures, and will probably be detected. (Your head is hottest, your hands are cooler.) Most PIR detectors count the number of times a target appears and disappears from their view, and if it happes (say) 3 times in 5 seconds, they will 'trip' and give an alarm signal. Slow changes are ignored, as are single pulses, which may be environmental changes (air conditioners) or electrical noise (RFI). Because of the way their optical system works, PIR detectors are most sensitive to targets moving ACROSS their field of view. Anything moving directly towards the detector is less likely to be detected, particularly if the rate of movement is low.
To help overcome this problem, and to reduce the likelihood of false alarms from small pets. moving curtains etc, PIRs are increasingly incorporating a second detection system ('Dual Technology detectors') with a microwave based Doppler detector being added to the infra-red detection unit. This system is most sensitive to targets moving TOWARDS the detector, and less sensitive to targets moving slowly across its field of view. By combining the two systems, the detector can be made very difficult to avoid, and by controlling the range and desired target size of the microwave unit, can be made less sensitive to false triggering events.
The answer left out light detectors which grossly replaced the bulky expensive ultrasonic devices. A light sensor is simply a photo diode biased to a point whereby any set disruption of light will trigger an output response
There are many types of motion detection alarms that can be used in and around the home. Most homeowners elect to use a system that integrates the use of infrared technology. These alarm systems emit beams of light. When there is an interruption to the beams, an alarm is activated. In the same respect, there are laser beam motion alarms that are part of many security systems around the nation.
The ultrasonic motion detection alarm is quickly gaining in popularity in home security. This specific type incorporates devices that, if touched, sound an alarm. If you want to ensure that your property is safe, and the safety of those that live in your home, a motion detection alarm can assist you in ensuring security.
Dr. Clarence Melvin Zener of Southern Illinois University invented the zener diode.
What is the approximate instantaneous voltage at 37 degrees on a 169 Vp sine wave?
169sin(37*) = 101.7067389 (round to 101.7)
*=degrees (function found on TI Calculators under "Angle") you can not do like that generally VpSIN(Wt
it is a bipolar junction transistor having p-type emitter & collector terminal and ,
n-type base terminal .
What is transition mode pulse width modulation?
How is it possible to test a diode with a multimeter?
The diode must be isolated from any parallel current paths to test. check resistance both directions through diode. readings should show an open (or very high resistance) one direction and a short (or very low resistance) the other direction. Usually, a failed diode will show an open both directions. Set the multimeter to check resistance, attach each meter lead to opposite leads on diode, note reading, then swap meter leads and compare readings.
How much time constants to charge or discharge a capacitor?
Theoretically, forever, because as the voltage on the capacitor approaches the source voltage, the available current to charge the capacitor approaches zero.
In practice, however, it simply depends on what you call "charged".
In the simple example of a capacitor being charged from a voltage source in series with a resistance, the voltage is given by ...
VT = Vs (1 - e -T/RC)
... so, if your definition of "charged" is 99% of VT then T would have to be 5 RC's or 5 time constants.
If a resistor is connected in series with the capacitor forming an RC circuit, the capacitor will charge up gradually through the resistor until the voltage across the capacitor reaches that of the supply voltage. The time called the transient response, required for this to occur is equivalent to about
5 time constantsor
5T
. This transient response time
T
, is measured in terms of
τ= R x C
, in seconds, where
R
is the value of the resistor in ohms and
C
is the value of the capacitor in Farads. This then forms the basis of an RC charging circuit were
5T
can also be thought of as
"5 x RC"
.
Why are both negative and positive voltages generated as the magnet passes through the coil?
In this context, 'negative' and 'positive' are used to indicate the sense, or direction, of the induced voltages, as voltages do not have electric polarity (+ or -). The direction of the voltage induced into a conductor is determined by the direction of that conductor relative to the magnetic field. As the coil rotates, the directions of each side of the coil reverse relative to the field, and the induced voltages reverse too.
In ujt what does the j stand for?
For many people the letters UJT stand for Unitary Junction Transistor.
What is the property of a conductor that opposes the flow of charge passing through it is called?
property of a conductor that opposes the flow of charge passing through it
