what is electrical noise?

  1. What is electrical noise

2.what causes electrical noise

3.how is it prevented in most cases

  1. What are some basic examples of electrical noise

Have you tried google?

What did it say?

https://www.google.com/search?q=what+is+electrical+noise&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a&channel=fflb

  1. Variations in your signal you don't want. c.f., "weeds"
  2. Everything generates noise or unwanted signals. Unless you are dealing with receivers or very high gain amplifiers, most of the noise you will worry about is actually interference - signals from other sources that couple to your circuit.
  3. Filters and lower impedances.

This sounds like a homework question to me, is it?

Why Google when you can start an interesting discussion with a group of electronic experts? Why don't you go Google "how to not waste your time by replying "Google it" "

KeithRB: 1. Variations in your signal you don't want. c.f., "weeds" 2. Everything generates noise or unwanted signals. Unless you are dealing with receivers or very high gain amplifiers, most of the noise you will worry about is actually interference - signals from other sources that couple to your circuit. 3. Filters and lower impedances.

What is filters and what do you mean by lower impedances? I don't understand the word impedance because some people say it is resistance and some people say it is a word only used in ac electronics and not dc

You can't have DC noise!

filters just mean filter the frequencies you don't care about to eliminate the noise out of your desired band.

For example, if you were making a ,low-fidelity audio amp, you might high-pass filter out frequencies below 100 Hz to eliminate 60 Hz hum, and low-pass filter out signals above a few kHz to eliminate hiss.

A filter is a circuit that has a specified variation in gain as a function of frequency.

Being an RF engineer, I tend to use impedance and resistance interchangeably, though you can think of it as resistance.

For example, if you hook up the test leads to your 10Mohm+ DMM, and just leave them hanging, you will read quite a bit of voltage. If you use the same wire but put a 10K ohm resistor across the leads, you will lower the voltage reading a lot.

Impedance is often used to describe drive capability of an output.
Say you had an output that created a high level by just using a 10K pullup resistor to 5V, and a low level that was created by an open drain (N-channel MOSFET), or open collector (NPN), transistor.
You would say this circuit had a high impedance high level output because it only has 5V/10,000 = 0.5mA of drive capability.
However, for the low level it would have a low impedance output as the transistors can sink many mA of current, say up to 40mA for a decent small transistor.
A part that used a P-channel MOSFET or PNP transistor to source current to an output pin to create a high would be said to have a low impedance output.

In very high speed circuits, you would want the output impedance of the source to match the impedance of the transmission line so the signal does not reflect - this is often done by adding a resistor at the end of the line, or perhaps two resistors, one to Vcc and one to Gnd.

Figures 5 & 6 here show the result of impedance mismatch and the ringing that results: http://www.fairchildsemi.com/an/AN/AN-393.pdf

Impedance is often used in RF work because in AC circuits, current and voltage can be, and often are, out of phase. So in that case, the impedance of the circuit is a complex function of resistance and reactance. Reactance is the out of phase component of the impedance.

Reactance is either 90 degrees leading, or 90 degrees lagging the resistance. So you don't just add the two to get impedance. Instead, you use the Pythagorean Theorem, where the resistance and reactance are the two sides adjacent to the 90 degree angle, and the impedance is the length of the hypotenuse.

Resistance^2 + Reactance^2 = Impedance^2

You can say resistance in AC circuits, if current and voltage are in phase. But generally no one says impedance in DC circuits, since there are no changes to be out of phase.

calvingloster: What is filters and what do you mean by lower impedances? I don't understand the word impedance because some people say it is resistance and some people say it is a word only used in ac electronics and not dc

Really and truly wikipedia will answer all of these questions and a great deal more besides, as will many many other sites.

Start here: http://en.wikipedia.org/wiki/Electrical_impedance

calvingloster: Why Google when you can start an interesting discussion with a group of electronic experts? Why don't you go Google "how to not waste your time by replying "Google it" "

Careful, you are making a persuasive argument for not replying to your questions at all.

Why don't you go Google "how to not waste your time by replying "Google it" "

We don't google it, because we already know the answer.....

Seriously, what response did you expect to your stupid first question ? Me to sit here for an hour and type out a 1000 word essay on the subject ?

What is filters and what do you mean by lower impedances? I don't understand the word impedance because some people say it is resistance and some people say it is a word only used in ac electronics and not dc

... and another 5000 word essay here ?

I don't understand the word impedance

Did they burn all the dictionaries in your country ?

I concur with the advice about wikipedia. I have written many 5000 word essays there, for millions of people to read and hopefully derive some benefit from. Not just you.

michinyon: Seriously, what response did you expect to your stupid first question ? Me to sit here for an hour and type out a 1000 word essay on the subject ?

I really think he does, yes.

Even worse: Some people are actually doing it

(instead of just linking to the Wikipedia article called "Electrical noise")

michinyon:

What is filters and what do you mean by lower impedances? I don’t understand the word impedance because some people say it is resistance and some people say it is a word only used in ac electronics and not dc

… and another 5000 word essay here ?

I don’t understand the word impedance

Did they burn all the dictionaries in your country ?

I concur with the advice about wikipedia. I have written many 5000 word essays there, for millions of people to read and hopefully derive some benefit from. Not just you.

Oh wow arnt u a clever boy! I can’t understand how people complain about how they will waste their time if they answer my questions, but ironically they waste their time by telling me that haha. If ur gana waste your time then simply don’t even bother to reply. You basically just wrote a 500 word essay just complaining now.

Impedance is a term which describes what current flows in a reactive load when its fed with an AC voltage. A reactive load is one which contains a mixture of capacitance , inductance and resistance. Its only applicable in AC circuits, as only in AC circuits can the voltage and the current be out of phase. Electrical noise is always AC. There are 3 types of electrical noise. 1/ Thermal noise which exists everywhere and cannot be gotten rid of , unless you own a refrigerator that can achieve temperatures of 0K. You normally only need to worry about this if you are building low noise RF amplifiers. 2/ Man Made noise which can be sometimes be reduced or avoided, using filters, shielding etc. Note, not all man made noise is noise , as to some people its useful data, but to others its noise. 3/ Natural noise, such as caused by natural events such as lighting bolts ,solar flares etc , cant do much about this.

Thunderstorm accompaniments, Thunder caused by Lightning.

Go to your library. Look up Johnsson Noise, Shot Noise, and anything else interesting which you find there.

Recommended Reading "The Art of Electronics" by Horovitz & Hill (I might have mistaken the spelling on this line)