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.

3,174 Questions
Electronics Engineering
Electrical Engineering
Circuits

What is Ohm's law?

Ohm's Law states: "The current flowing through a conductor is directly proportional to the applied voltage, provided the temperature of the conductor remains constant."

It specifically refers to conductors and not resistors. And it takes into consideration the need to maintain a given temperature as the voltage and current vary. At the time, Georg Ohm already knew that allowing the temperature to vary would break the constant ratio.

Keep in mind that this was a historic new understanding that he had discovered was applicable to various conductors (metals).

Ohm's Law is by no means a universal law, and very few materials or electrical components actually 'obey' Ohm's Law. Those that do (some metals) are termed 'linear' or 'ohmic'; those that don't (most) are termed 'non-linear' or 'non-ohmic'.

Simply put, if the graph of voltage against current, plotted for variations in voltage, is a straight line, then Ohm's Law applies; if the graph is not a straight line, then Ohm's Law does not apply. And very few materials/devices produce a straight line graph. Based on this, you could say that 'Ohm's Law' is not a 'law' at all, but simply describes the behaviour of a limited range of materials.

So Ohm's Law doesn't apply to heated metals such as tungsten filaments, or to circuit components, such as diodes and to practically all other electronic devices.

The basic unit of electrical resistance was given the name 'The Ohm' in honor of Georg Ohm. The symbol for the unit is Ω, pronounced Omega. The ratio of a given voltage to resulting current will always tell us what the resistance happens to be for that particular instance. This is because the ratio of voltage to current is, by definition, resistance - however, this has nothing whatsoever to do with Ohm's Law, but is simply a definition of resistance!

E = I R

Voltage = Current times Resistance

As the alternate answers below clearly indicate, there is a widespread misunderstanding regarding Ohm's Law. Answer Resistance defines the relationships between (E) electromotive force in Volts and (I) current in Amperes. One ohm is defined as the resistance value through which one volt will maintain a current of one ampere. In other words, an ohm is a volt per ampere.

(I) Current is what flows on a wire or conductor like water flowing down a river. Current flows between points of different voltage. Current is measured in (A) Amperes, abbreviated: amps.

(E) Voltage is the difference in electrical potential between two points in a circuit. It's the push or pressure behind current flow through a circuit, and is measured in Volts.

(R) Resistance determines how much current will flow through a component. Resistors are used to control voltage and current levels. A very high resistance allows a small amount of current to flow. A very low resistance allows a large amount of current to flow. Resistance is measured in Ohms.

Answer The statement taught in electrical training is "Current is directly proportional to the applied EMF and inversely proportional to the resistance of the circuit".

Ohm's law: When there is a potential (Voltage-V) different between two ends of a conductor a follow of charges will be created (The current-I) through this conductor which is directly proportional to the voltage difference and inversely proportional to the resistance of the conductor (Resistance-R ).

I α Vdifference

I α 1/R

I=Vdifference/R : Current increases with increase of voltage, but decreases with the increase of the resistance

Answer Ohms Law states that the amount of current that passes through an object is directly proportional to the potential voltage across that object, and inversely proportional to the resistance, or electrical impedance, of that object. In other words: * as voltage goes up, the current goes up by the same proportional amount * as the impedance goes up, the current is reduced by the same proportional amount. Ohms Law can be stated mathematically as:

I = E/R Where: I is the current, E is the voltage, R is the resistance

As you can see from the above formula, if the voltage were to double, then so would the current. If the resistance were to triple, then the current would be one-third of its former value. You can use Ohms Law to calculate any value if you know the other two. These are expressed mathematically as: V = I x R (to calculate Voltage) R = V / I (to calculate Resistance) In the above calculations, V is measured in 'volts', I is measured in 'amperes' (or amps), and R is measured in Ohms.

Ohm's Law states Voltage = Current x Resistance. Except in unusual circumstances the resistance "R" is a constant. When you increase voltage, current increases.

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Ohm's Law states that 'the current flowing through a conductor at constant temperature is directly proportional to the potential difference across that conductor'.

Ohm's Law is by no means a universal law, and onlyapplies to those conductors or devices where the ratio of voltage to current is constant over a wide range of potential differences. These materials are termed 'ohmic' or 'linear', whereas those materials and devices that do not obey Ohm's Law (and there are a great many!) are termed 'non-ohmic' or 'non-linear'. Examples of non-ohmic materials and devices include tungsten (lamp filaments), diodes, electrolytes, etc.

The ratio of voltage to current is termed resistance (R = E/I), and is derived from the definition of the ohm, and not (as many people think) from Ohm's Law. This equation can be applied to both ohmic and non-ohmic materials and devices, so applies whether or not Ohm's Law is followed.

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Circuits

What is DC Resistance?

The resistance of a conductor is determined by the length, cross-sectional area, and resistivityof the conductor. Since temperature affects resistivity, resistance is indirectly affected by temperature.

Resistance is directly-proportional to the length of the conductor and inversely-proportional to its cross-sectional area, and resistivity is its constant of proportionality. If the length of the conductor is expressed in metres, and the cross-sectional area is expressed in square metres, then resistivity is expressed in ohm metres. Using American units of measurements, however, where length is expressed in feet and cross-sectional area in circular mils, resistivity is normally expressed in 'ohm circular mill per foot' (not, as often seen in textbooks: 'ohms per circular mil foot'!).

In the case of d.c. current, the charge carriers distribute themselves across the entire cross-sectional area of the conductor. In the case of a.c. current, however, due to what is known as the 'skin effect', there is a tendency for the charge carriers to move closer to the surface of the conductor -this acts to reduce the effective cross-sectional area of the conductor and, thus, raise its resistance. So a conductor's resistance to a.c. is somewhat higher than it is to d.c., and is generally termed its 'a.c. resistance'. A.C. resistance increases with frequency (and should not be confused with 'reactance' or 'impedance').

465466467
Biology
Temperature
Circuits

Why does absorption of a membrane increase with temperature?

This is a very simple question with rather a complication set of answers. Movement of some molecules or substances across a membrane only increases between the temperatures of 1 to 37 degrees Celsius (in most organism/cellular systems). At temp. greater than 37 Celsius the membrane proteins involved in transport become denatured. One has to consider the main processes of movement of substances across a membrane i.e ranging from passive diffusion and osmosis and including active transport systems and end/exocytosis etc.

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Electronics Engineering
Physics
Electricity and Magnetism
Circuits

What are the factors on which resistance depend?

It depends on the intermolecular structure of the individual material. It varies for various material.

Generalised formula for calculating the resistance of any material is :

R = k* L/A

Where

R = Total Resistance.

K = Specific Resistance of the material.

A = cross-sectional area of material for which resistance is measured.

334335336
Circuits
Muscular System

What is threshold voltage of a muscle?

1.5

319320321
Electronics Engineering
Circuits
Waves Vibrations and Oscillations

What type of feedback is used in the oscillator circuit?

There are many different types of oscillator circuits, the majority of which use positive feedback.

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Electronics Engineering
Electrical Engineering
Circuits

Is capacitor polarity sensitive?

Some capacitors are polarity sensitive; some are not. It depends on the design. Electrolytic capacitors, for instance, are polarity sensitive, while ceramic disc capacitors are not. You can generally tell, if the capacitor is marked with polarity signs, such as + and -, if it is or not.

283284285
Circuits
Physics

How can you convert the voltage into milli amps?

Voltage is a property of electrical potential. Amperes (and miliamperes) are the units of electrical current. Even though these are related to each other in a circuit, they are not the same thing, and they cannot be "converted" into each other.

Also, these properties are only related through a "load" the circuit provides (the resistance and inductance of the circuit), and make sense only when related to each other this way. If there is current, there will be voltage as well, but if there's only voltage, there will be no current unless there is some resistance as well (even a wire has resistance) - otherwise the circuit is "open" and no charge is flowing.

In a simple circuit with a voltage source and resistor:

milliamps = voltage*1000/resistance.

If your circuit has diodes, capacitors, inductors, etc. it gets much more complicated.

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Circuits

Which one is better potentiometer or voltmeter?

Neither is better or worse than the other. A potentiometer is an adjusting device usually for voltage while a voltmeter is a device for measuring the voltage. They are just two different things.

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Chemistry
Circuits

Why is melting point of fuse low?

Fuses are used to protect circuits from overload by being the part that fails first. To do their job they have to be the weakest link in the chain. If they had higher melting points something else instead of the fuse might break first, making the use of a fuse quite pointless.

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Electronics Engineering
Circuits

Is there a LM3914 circuit that ranges 8 to 18 volts?

I just stopped using the LM3914, and now use a quad comparator (LM339) with a simple voltage divider. It's a little bulkier but at least it works.

204205206
Home Electricity
Electrical Engineering
Circuits

Why was 120V chosen as the standard voltage of homes in the US and not some other voltage?

The reason that 120v service was chosen, was economic. Originally electricity was delivered to homes, and most businesses, for a single purpose and that was lighting. Can openers, TVs, washers, dryers, electrical factory machinery, etc. came later. At the time the most cost effective form of light bulb was a carbon filament bulb that operated best (optimally) at 100v to 110v. This, adjusted for transmission voltage drop, set most supply lines at 120v.

Supplemental and Related Information:

By the time cost effective, and higher voltage, metal filament bulbs were brought to the market, most of the cities in the USA were already running 120v supply lines. Europe was just starting such systems and opted for higher voltage supply lines.

Higher voltages are used for long distance transmission and power distribution because more power can be transferred over the same size wire at a higher voltage (lower current). Power generation plants often use voltages in the hundreds of thousands, 115,000 to 165,000 of volts to move power over long distances. For lines of up to 20 miles long around a city, 2400 volts works well to reduce the voltage loss in the wires.

In North America, the electrical power lines going to residential streets and roads are operated at a primary voltage of 7200 volts. This voltage (12500/1.73 = 7225) is one leg from a three phase 12500 volt primary line. On the secondary of the transformers it is center tapped to provide 120 volts from each 240-volt leg to the center point. The center point is electrically neutral. The actual measured voltage in your house receptacle circuits will normally be 110 to 120 volts. All appliances are rated for the minimum operating voltage (110-115). This is the cause of confusion about the actual level of the supply voltages.

Different nominal voltage level and frequency standards are used in different countries. Europeans - and many other countries around the world - use 50 Hz (cycles per second) as the alternating frequency, not 60Hz as is used in North America and, again, many other countries around the world. The reason to use a higher voltage is that it is more economical because the current is less, so the wires can be smaller. On the other hand, the reason to use lower voltage in homes is safety: the lower the voltage, the safer it is.

If you have 10 amps drawing on one leg of your 240/120 service, and 10 amps on the other leg, the I2R losses are one fourth what they would be if you had 20 amps on just the one leg.

The Europeans use 415/240 (415/1.73 = 240), so their I2R losses are 1/16th of our 120 volt losses, with 20 amps drawing on just one leg.

480 V center tapped (split phase) is used in the UK only rarely, typically in rural areas to supply an isolated small group of houses that can be fed off a single phase overhead spur. Most houses and small businesses are supplied with 240 V single phase taken from a 415 V three phase local system, fed from a transformer of up to 700 KVA connected to the 11 kV distribution system. The voltage is mostly 240 V but is nominally described as 230 V with a suitably wide tolerance, to comply with European standards.

Originally, the service voltage was about 90 volts direct current, which was Edison's plan. Tesla proposed that the electrical grid be alternating current (AC) and competed with Edison for the first generating plant to be built in the State of New York at Niagara Falls. Edison proposed a DC system and Tesla an AC system. History tells us that Tesla won the competition, and because of that the industrial revolution was quickly accelerated. Had Edison won we would probably still be in the dark ages because of the inefficiency of transmitting DC current over long distances. While Edison was promoting the electrical light bulb around the country, almost every town required its own generating station because DC would lose so much in the transmission that it became unusable after only a couple of miles.

Tesla also had invented the poly phase alternating current generators that provided for the ability to generate the voltages necessary for long distance transmission. Tesla kept the voltage about the same as what Edison started but raised it to the 110 volts alternating current (VAC) because of the higher related voltages of 220 VAC and 440 VAC, which were integral to the more efficient poly phase generators.

The standard voltage available in most parts of the country (US) is now nominally 120 VAC volts +/- 10%, and can vary from 108 VAC to 132 VAC. It's usually around 117-118 VAC.

Transmission distances, the actual power needed in a neighborhood, cost, efficiency and safety issues dictate service parameters. Common distribution voltages run up to 16,000 volts. 12,000 is very common but there is still a lot of activity adding on to legacy distribution grids at lower voltages. A 2400 volt primary is very low for a distribution transformer.

In actuality power transmission is over many miles and the transmission voltage is more then 110kV. In fact interstate transmission is in the range of close to 500kV. At a substation it is reduced to 16kV for local area distribution. Transmission for the whole of the grid in North America is all tied together . Why? For economy and reliability. For example in the Summer some states do not use air conditioning but in Las Vegas, Nevada they do, so they actually buy the power from Canada in the summer because it is cost effective and reduces the need for more generation plants. Even then reserve spin power must be sustained for peak demands. Because power plants cannot produce near instant acceleration to meet new demands. In many cities and other peak demand areas, specialist peakers work to ensure that the the integrity of the grid is always maintained. 240 v is standard for the USA but only one phase is used and the transformer center tap is grounded, making it safer. Also, the main frequency of 60 Hz produced by power generation is not as stable as some people think. It varies throughout the day as loading changes but the controllers must legally ensure that it averages 60Hz over a complete day so that electric clocks using synchronous motors remain accurate.

204205206
Circuits

How does a pressure switch work in a circuit?

when the pressure switch detects some pressure it turns the circuit on and sometimes depending on the programming in accordance with the amount of pressure it could do different things.

187188189
Electricity and Magnetism
Electrical Engineering
Circuits
Waves Vibrations and Oscillations

What is sinusoidal voltage?

A sinusoidal voltage is an oscillating voltage that can be described mathematically through the use of a sine function.

~

187188189
Car Electronics and Lights
Electronics Engineering
Circuits

Signal conditioning circuit of potentiometer?

you can use an impedence converter or a voltage follower

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Electronics Engineering
Colors
Circuits

Why are circuit boards green?

That is just the conventional color of the insulating varnish "mask" used to protect the board. It could be a different color, but green was selected as it contrasts well with copper traces allowing them to be seen through the "mask". Up until the late 1950's, circuit boards were usually brown in color. The brown boards had no "mask" on them, the traces were protected with solder dip. Brown is the color of the paper-epoxy or paper-phenolic board material used.

165166167
Electrical Engineering
Circuits

What is an arc suppressor?

An Arc Suppressor is a combined Resistive-Capacitive device that is applied across the contacts of a relay or motor-starter to suppress surges on startup or open opening of the contact. This is necessary to absorb the energy potential across the contact and prevent an arc. This prolongs the life of the electrical contact, reduces noise in the circuit, and in some cases may be part of personnel safety. The device must be sized according the potential that might be seen across the contacts.

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Circuits

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.

149150151
Circuits

What are the functions of execution unit in 8086 Intel?

Basically the function of execution unit in 8086 is to perform all arithmetic and logic operations.It tells the Bus Interface unit(BIU) where to fetch instructions and data from.It has 4 components:Control circuitry,ALU,Flag registers and general purpose registers.

1.control circuits-it directs all the internal operations.

2.ALU-performs all logic operations.

3.general purpose registers-used to store data during execution.

4.flag registers-it has a 16bit flag register containing 9 flags that are set for certain conditions during any operation.Ex.carry flag(whenever there is a carry).

It also has a decoder to decode the fetched instructions.

149150151
Electronics Engineering
Electrical Engineering
Circuits

What is a relay circuit?

A relay circuit is typically a smaller switch or device which drives (opens/closes) an electric switch that is capable of carrying much larger current amounts. Or a circuit which operates the coil or electronic actuator from one source and uses a separate power source to drive an isolated device. Generally speaking, a relay circuit is a circuit that uses a small mechanical switch or a semiconductor device (with associated circuitry) to energize a relay, which will then close a contact set to complete another circuit. This system is used by most people on a daily basis, and it is used to start a motor vehicle. The key switch (ignition switch) is turned to "start" and 12 volts (approximately) is applied to the starter solenoid (which is a big relay). The coil is energized, it shuts contacts, and the battery voltage is delivered through the heavy contact set (for high current capacity) to the starter motor. There are variations on this theme to which the term relay circuit can be applied, but the idea remains the same: a small switch of some kind controls switching in another (usually higher voltage and/or current) circuit. It could be argued that the telegraph is a relay circuit. Remember those old westerns? When a telegraph key is pushed down (thus completing the circuit), a remote (relay) coil is energized. The magnetic field created by energizing that coil pulls down an armature with the objective being to make a "click" instead of it being to close some electrical contacts. An early and dramatic application of the simple relay circuit, the telegraph, yes? A RELAY CIRCUIT DOES NOT IMPLY MASSIVE CURRENT SWITCHING. It is a means to isolate one source to another.

113114115
Electrostatics
Circuits

What is the internal resistance of leclanche cell?

pata nahi

131132133
Circuits

What are the four parts of any electrical circuit?

The three essential parts of any electrical circuit are: a power source (like a battery or generator), a load(like a light bulb or motor) and connectors (wires) to join them together.

A fourth part, that is always a very important thing to have in most circuits, is a control device such as a switch, circuit breaker or fuse.

939495
Circuits

Construction of mosfet in depletion region?

To make a depletion MOSFET, the channel must be doped with carriers; this is in total opposite to an enhancement MOSFET which avoids carriers in the channel at all cost. (because the carriers in the channel become the subthreshold leakage current)

Since you need to pinch the channel against the substrate to guarantee to turn off the channel completely, there must be a reverse bias between the substrate and the source terminal. As a result, the source terminal of an N type depletion MOSFET must be tied to Vdd. This is also a complete opposite to enhancement MOSFET.

In order to turn off the channel quickly, the carriers in the channel of depletion MOSFET are usually planted shallowly. This is a drastically different from enhancement MOSFET that carriers must be planted deeply into source terminal in order to support a large diffuse current.

The construction of depletion MOSFET thus requires far less diffusion time than enhancement MOSFET.

129130131
Electronics Engineering
Electrical Engineering
Circuits

How do you analyze the internal circuit of LM386?

One of the beauties of an integrated circuit is that you can regard the package as

a 'black box' characterized by its published operating parameters, and you don't

need to analyze the internal circuit.

If you've been assigned to analyze the internal circuit, then you're part of a class

or group of people who have been given the tools necessary to do it. Just go

ahead and dig into the nine transistors there in the LM386. There's a single-stage

differential amplifier with a few feedback components, and there's also what appears

to be a voltage regulator. There's not really that much in there, and you shouldn't be

scared off by the use of PNP and NPN transistors in cascade.

The whole thing is just an academic exercise anyway ... notice that the drawing

in the data sheet is labeled "equivalent schematic", and doesn't really represent

everything that's actually on the chip.

125126127
Electronics Engineering
Electrical Engineering
Circuits

What is the necessity of wave shaping circuit?

chutiya bahanchod

106107108

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