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Circuits
Overachieving and under-appreciated, circuits are the foundation that our technological society is built on. Now's your chance to find out not only how they work, but why. Questions regarding the physics behind voltage, resistance, capacitance, inductance, transistors, LEDs, switches, and power supplies; and how they're used to create analog and digital circuits, should be directed here.
1,646 Questions
What the purpose of the diode rectifier used with a ac analog voltmeters?
The analog voltmeter uses a dial, which changes its position in accordance with applied voltage - however, this voltage must be DC in order for this to work (it's through either thermal or magnetic expansion). So, the AC must first be rectified into DC, before any measurement can take place.
Of course, rectifying AC into DC does increase the voltage (as it must - this action multiplies the voltage value by the square root of two), so before the measurement can occur, this increase is properly sanitized by associated circuitry (for example, a voltage divider could be used).
What is the formula of power being dissipated in a resistor?
Voltage times current. You obtain current from the division of voltage and resistance, so:
I[A] = U[V] / R[ohm]
and
P[W] = U[V] * I[A]
it follows, that
P[W] = U[V] * (U[V] / R[ohm]) = U[V] ^ 2 * R[ohm]
So, voltage squared divided by resistance will give you the power that will be dissipated in a resistor. Whether the resistor will take that abuse is up to its power dissipation rating, however.
Why alternatig current electricity is better than direct current?
Nobody said it was. Well, maybe except Nikola Tesla and George Westinghouse... *chuckle*
Each type (AC and DC) has unique advantages over the other in certain situations.
For example - AC is much more useful when transmitting power over distance, as power lost with AC has much more to do with parasitic inductance and capacitance than it does with resistance. AC is also the form in which most of our electricity is generated (electrical generators are turbines, they produce AC). And on top of that, AC is easily manipulated using transformers, which do their job thanks to alternating magnetic fields (DC doesn't produce an alternating magnetic field).
The main disadvantage of AC would be its lethality to all living creatures, and of course - AC is useless when it comes to state-based electronics. Most AC devices are also rather bulky and impractical to carry around for long.
DC, on the other hand, is much more useful in low-voltage applications where power doesn't need to go far, and wherever logical states are considered. As such, most electronics is mainly DC (with a few notable exceptions throughout the years). Your computer, radio, television set, even your wristwatch - they all run on DC, internally. Yes, the TV set uses DC as well, only at much higher voltages (typically around 180V/320V to start, and then a couple kV to drive the deflection coils and the electron gun).
Then again, DC was dropped in favor of AC when it came to power distribution - and why? Well, as I've mentioned before, DC transmission suffers much higher power losses over distances, as conductor (wire) resistance comes into play - this energy is wasted away as heat. This also limits the effective range of power distribution network to a couple of hundred kilometers (beyond which consumers would receive too little power to be of any use).
So, as it should already be evident, each form has its strong and weak points. None is better than the other - they're both different forms of the same thing - but each is better suited for some applications over others.
I hope this answers your question.
What does the resistance in an electrical circuit limit?
Current flow. It's also worthy of noting that a resistor doesn't limit-by, it limits-to, and the current is dependent on the voltage.
I[A] = U[V] / R[ohm]
It's also worth to note, that the power flowing through said resistor with resistance R is I[A] * U[V] for DC circuits - helps to remember this well when picking appropriately-rated resistors for replacement.
Example: let's say we have a 20-ohm, 2W resistor. If we place it in a circuit with 5V, we will get 5V / 20ohm = 250mA (0.25A) of current flowing through the resistor. The power the resistor will "see" is 250mA * 5V = 1.25W, so it's safe.
But let's now put that same resistor in a 12V circuit. The current flowing will be 12V / 20ohm = 600mA (0.6A), and the power will be 600mA * 12V = 7.2W, so the resistor will burn.
What is the total resistance of a circuit with a 75 ohm and a 150 ohm resistister in parallel?
The equivalent resistance of 75 ohms and 150 ohms in parallel is
(75 x 150)/(75 + 150) = 50 ohms
What is the most reliable test instrument to use in troubleshooting in a digital circuit?
The most robust device for all kinds of electronic troubleshooting is also the simplest - a multivoltmeter. Since almost any kind of measurement can, with the right equipment, be converted to appropriate voltage levels, many things (including resistance, capacitance, inductance and even frequency) can be measured using this simple tool.
However, for more complex analog signal processing circuits, and most digital circuits, an oscilloscope is an invaluable tool. It helps if the scope's bandwidth can go as high as 100MHz or more, if possible, esp. in the RF-decoding circuits (antenna circuits in TVs and radios) and in CRT television sets (deflection circuits, mainly). Still, having the best tools means nothing if you do not have the knowledge to understand the readings (or to connect the device properly).
Ultimately, the most important and the most reliable troubleshooting tool for any kind of circuit is your brain. :)
How you calculate the resistance of a capacitor?
There's nothing to calculate. Until it fails and must be replaced, the resistance of
a capacitor is infinite. A measurement with a typical ohmmeter will show that the
capacitor is open.
Should a motor with a start capacitor have a start relay?
The compressor motor employs both a start and run winding. The run winding is energized during the complete cycle of operation, whereas the start winding is energized only during the starting period. The current-operated type of relay has a coil connected in series with the run winding of the compressor. Some current-operated relays plug directly onto the compressor while others do not. Most relays are mounted in a case located on the compressor. When the thermostat closes, the compressor attempts to start, drawing heavy current through the run winding and the relay coil. This strong current flow through the relay coil creates a magnetic field strong enough to cause the start contacts to lift and close, energizing the start winding. When the compressor reaches approximately 3/4 running speed, the current flow through the relay coil decreases (due to the countering electrical magnetic field in the motor) and as the magnet weakens, the start contacts fall open. This type of relay must be used with an overload protector and must be mounted in an upright position, so that the contacts can fall freely to the "open" position.
What letter is used as a reference designator for a resistor?
Commonly and typically the letter ' R '. But there's no law,
and it really doesn't matter.
Will jumping a car batery damage alternator diodes?
Not if you jump it from the battery or electrical system of another car.
Do I need a voltage converter for UK?
That depends on where you're coming from, and on where
the appliances you bring with you are designed to operate.
What voltage is used in USA city hotels?
The standard nominal mains supply everywhere in the USA is 120 volts AC, 60 Hz.
What is feature size in transistor?
Integrated circuit processes are characterized by the feature size, which is the minimum size of a transistor or a wire in either the x or y dimension. Feature sizes have decreased from 10 microns in 1971 to 0.09 microns in 2006; in fact, we have switched units, so production in 2006 is now referred to as "90 nanometers," and 65 nanometer chips are underway. Since the transistor count per quare millimeter of silicon is determined by the surface area of a transistor, the density of transistors increases quadratically with a linear decrease in feature size.
What causes contact chatter in electrical circuit?
Overload can cause contact chatter. Once the contact closes, the voltage in the circuit collapses and that causes the relay to drop out. At this pint the relay energizes, since the voltage is back. This cycle will continue on.
What happens in a bad capacitor?
In essence, a failed (bad) capacitor appears as a "short" in the circuit, as opposed to a failed (open) resistor which appears as a "break". Unless of course the capacitor has exploded - in that case it'll probably be a "break" as well, but don't count on it.
It depends on the function of the capacitor. If the capacitor is used to 'smooth out' (filter) unfiltered voltage, this function will be lost and in addition, the capacitor will "load down" the voltage rail it's supposed to smooth out. If, on the other hand, the capacitor is part of an oscillator circuit (be it a standalone oscillator, an oscillator network, or timing source for an integrated circuit), the frequency of the oscillation will be greatly offset from the ideal value, and this may appear as many different problems (instability and lack of synchronisation with signals among others) which wouldn't easily be tracked down to the bad capacitor.
If, on the other hand, you were asking about what chemical and physical events take place within the capacitor as it fails, this question should be filed under "Chemistry" or "Physics" at least in additon to, if not in the stead of, "Circuits", and it would be wise to include a word or two asking about the reactions within the electrolyte itself (as most failed capacitors are electrolytic).
Can you use capacitor as a battery?
In a sense, a capacitor IS a battery. But a very small one. A typical 33uF capacitor will hold about 33uC - that is, 33uA (microamperes) per second. At 16V potential, that will be around 528uC of charge (or 528uA in a second).
In contrast, a 1.5V AA battery can typically provide between 1.5 and 1.8Ah (ampere-hours) at 1.5V. That is - a device drawing 1.8A (amperes) will keep running off of such a battery for about an hour. The same device would consume the charge stored in our 33uF capacitor in 1/54545th of a second.
So in the end - no, it's not likely that a capacitor would be a feasible means to store large amounts of charge.
Rather, capacitors are used wherever oscillating circuits are needed (a basic R-C oscillator can be built from a capacitor and a resistor), and wherever "voltage smoothing" is required - the amount of charge a capacitor holds wouldn't run a small pocket light, but it would be enough to "fill in the gap" if a momentary voltage drop occured in a line-powered device.
Capacitors are also used in this very manner to reduce ("de-couple") mains hum (50Hz or 60Hz, depending on the continent) by "filling the voids" that are left over in the rectified DC voltage when the AC voltage phase passes through 0V.
Why do you treat water within a closed circuit cooling system of a building?
To deoxygenate the water, thus preventing corrosion
What are all of the different electrical voltages in the US?
This is your lucky day. The standard mains supply
everywhere in the US is 120 V AC 60 Hz.
What does one-quarter W mean for a rated resistor?
It means that the resistor will safely dissipate the heat involved in transporting that much power through, without burning up/out. If you exceed that rating, the resistor will become too hot for its own good.
Power is always linked with Voltage and Current, and Current is linked with Voltage and Resistance of the resistor. You will do well to remember the tandem of laws:
Power [Watts] = Potential [Volts] * Current [Amperes]
and
Current [Amperes] = Potential [Volts] / Resistance [Ohms]
For example, if you have a 100ohm resistor rated at 0.25W, then to satisfy that requirement, a voltage of no more than 5V can be applied to it, because 5V / 100ohm = 0.05A, and 0.05A * 5V = 0.25W.
What happens if you remove the diodes from an alternator?
If you would remove those diodes, it would generate AC power instead of DC.
When the alternator makes electricity it makes it in AC, but your cars battery runs on DC. Those diodes calm down, if you will, the current making it DC.
So if the diodes are removed please don't put it back in your car, you will blow up your battery. No one wants that.
What should be done with unused TTL output?
Unused TTL inputs should never be left open. Depending on how their logic levels
will affect the operation you want from the device, unused inputs should always
be tied to either the +5v supply (logic 1) or to the circuit ground (logic 0). If an
input is left open ("floating"), then it can assume either logic level, and you literally
never know which state it's in.
Why CE configuration of BJT transistor gives 180 phase shift?
when the switch the emitter-base junection is an opnd circut and heance the value of input or base curent is zero.
Why diode rectifier need transformer?
A diode rectifier is a device (or four discrete devices- namely diodes), which converts alternating current (AC) into direct current (DC). It doesn't need a transformer as such. The transformer is there to convert the high voltage 'low energy' AC (like mains power) into low voltage 'high energy' AC (like 12V or 16V), which is then converted using the rectifier bridge into DC.
These are two separate devices, which nonetheless frequently appear together. This is because it is the easiest to transport power over large distances (say, from power plant to your house) using high voltage AC, so that a lot less energy is lost due to heat or weather along the way, but high voltage AC isn't the most useful form of energy for electronic devices. Electronic devices "like" the low-voltage (but 'high energy') DC, so the transformer first "steps the voltage down" (and "converts" the "volts" into usable "amperes"), and then rectifies it into DC, which is what many transistors (of which most electronics are made of) use to do some work for us (like playing a radio station).
So, the rectifier bridge doesn't need a transformer, but it is useful for many applications to have it.
Consider, on the other hand, your picture tube TV (the CRT ones, with the big, bulky rear ends?) - these picture tubes required high voltages, and so the line voltage wasn't stepped down using a transformer at all! In fact, it was actually stepped UP to the levels of several kilovolts needed to emit electrons which draw nice pictures on the front of the picture tube.
A Field Effect Transistor is a device with a single channel (conductor between two of the terminals). This channel is turned on an off by a voltage applied to the third terminal which is connected to the conducting channel in a J fet (junction Fet) or isolated from the channel in a Metal Oxide Semiconductor (MOS) fet. To keep the explanation simple, an enhacement mode MOS FET pulls charge carriers (electrons for N channel and holes for P channel) into the channel so its resistance decreases. This turns it on. By removing this voltage, charge carries move out of the channel and the FET turns off. It can be turned on partially by putting a small voltage on the control terminal called the GATE. In an N channel FET, the charge carriers (electrons) move from the SOURCE terminal (-ve) to the DRAIN terminal (+ve) when the FET is on. The voltage on the GATE is applied with respect to the SOURCE. In a P channel enhancement mode FET, charge carriers (holes) are also pulled into the channel in the same way but because the charge carriers are holes, the SOURCE is the +ve terminal and the DRAIN is the negative. The holes referred to are gaps in the crystal lattice of a substance like silicon which is doped (impurities added) with aluminum which has only 3 electrons in the outer shell instead of 4 like silicon. In a depletion mode FET, everything is the same except in reverse. Charge carriers are pushed OUT of the conducting channel.
