What does negative voltage supply mean?
- Thread starter BrendanP
- Start date
Brendan
To save time wandering aroung Googleland,
Some excellent basic info here:
http://www.kpsec.freeuk.com/voltage.htm
http://www.kpsec.freeuk.com/imped.htm
e
To save time wandering aroung Googleland,
Some excellent basic info here:
http://www.kpsec.freeuk.com/voltage.htm
http://www.kpsec.freeuk.com/imped.htm
e
Andrew Cowan
Senior Member
Say you have a 9V battery. If you call the positive terminal 0V, what do you call the negative termanal?
-9V.
A
-9V.
A
BeanieBots
Moderator
Well voltage has been answered nicely, so here's the other bit.
Resistance ONLY applies to resistors.
Impedance is to resistance what velocity is to speed.
Impedance includes time and phase.
For example, an inductor's impedance is a function of frequency.
So is a capacitor's.
If you put two resistors in parallel, the combined resistance goes down and is simply the sum of their condcutances. 1/R' = 1/R1 + 1/R2.
However, that simplified equation would not work if you were to put an indcutor and a capacitor in parallel. You would need to include the time domain in the summing equation.
Hence, when people talk of input impedance, they mean the WHOLE thing. Not the DC RESISTANCE part.
Resistance ONLY applies to resistors.
Impedance is to resistance what velocity is to speed.
Impedance includes time and phase.
For example, an inductor's impedance is a function of frequency.
So is a capacitor's.
If you put two resistors in parallel, the combined resistance goes down and is simply the sum of their condcutances. 1/R' = 1/R1 + 1/R2.
However, that simplified equation would not work if you were to put an indcutor and a capacitor in parallel. You would need to include the time domain in the summing equation.
Hence, when people talk of input impedance, they mean the WHOLE thing. Not the DC RESISTANCE part.
BeanieBots
Moderator
Not quite true. Impedance itself is always real but you will need "imaginary" numbers to calculate it.Impedance is also often imaginary, (not real)
Resistance and impedance more-or-less describe the same phenomenon.
The subtle difference is that resistance is typically a DC (direct current) measurement, whereas impedance is an AC (alternating current) measurement.
For instance, if you measure a loop of wire with a DC ohm meter, you will get 0 Ohms, which is the DC resistance. However, if you then put an AC signal across the loop and measure it's impedance (you can do this with an oscilloscope in XY mode where 1 axis is the voltage and the other axis is current, and computing impedance from the slope of the line since R=V/I), you will observe that the impedance will start out at or near 0 for low frequencies, but then increase as you increase the frequency (incidentally, this is due to the inductance of the wire).
The subtle difference is that resistance is typically a DC (direct current) measurement, whereas impedance is an AC (alternating current) measurement.
For instance, if you measure a loop of wire with a DC ohm meter, you will get 0 Ohms, which is the DC resistance. However, if you then put an AC signal across the loop and measure it's impedance (you can do this with an oscilloscope in XY mode where 1 axis is the voltage and the other axis is current, and computing impedance from the slope of the line since R=V/I), you will observe that the impedance will start out at or near 0 for low frequencies, but then increase as you increase the frequency (incidentally, this is due to the inductance of the wire).
BeanieBots
Moderator
More to the point, V & I will not be in phase.
Hence, R=V/I will be different at any given moment in time.
Hence, R=V/I will be different at any given moment in time.
Just think, with nearly 6 hours of Googling and Alta-Vista-ing and Wiki-ing you could have found a concise answer , with graphs, pictures and everything you could have asked for...
So, next question; whats the speed of light in a volume at absolute zero K in a field of zero gravity? Discuss how this could affect quantum theory related to the use of Superconductors and supercooled opto-electronic logic gates. Feel free to burble on about tachyons too if you think it will impress.
So, next question; whats the speed of light in a volume at absolute zero K in a field of zero gravity? Discuss how this could affect quantum theory related to the use of Superconductors and supercooled opto-electronic logic gates. Feel free to burble on about tachyons too if you think it will impress.
Final exams?
Q: Draw a neat labelled map of the world. Be sure to include all street names and bus stops.
or
How come this question is worth 20 marks when the answer is "Yes"?
Re negative voltages. Take two 9V batteries and put them in series. Call the negative of the lower one 0V. You will have 9V where they are joined, and 18V on the positive of the higher one. Or to look at it another way, call the join 0V, and then you have -9V on the negative of the lower one, and +9V on the positive of the higher one.
It is a bit semantic as to which one you use. If those batteries and their circuit are not connected to anything else, then you might use 0V. But say you connect 0V to the case of a computer and that case is connected to Ground. Now your 0V becomes ground. And this has real consequences, because a wire in a moist environment with a reasonably low resistance to ground (say a nail in a bit of wet wood) with +9V on it will corrode, but a nail with -9V will not.
Q: Draw a neat labelled map of the world. Be sure to include all street names and bus stops.
or
How come this question is worth 20 marks when the answer is "Yes"?
Re negative voltages. Take two 9V batteries and put them in series. Call the negative of the lower one 0V. You will have 9V where they are joined, and 18V on the positive of the higher one. Or to look at it another way, call the join 0V, and then you have -9V on the negative of the lower one, and +9V on the positive of the higher one.
It is a bit semantic as to which one you use. If those batteries and their circuit are not connected to anything else, then you might use 0V. But say you connect 0V to the case of a computer and that case is connected to Ground. Now your 0V becomes ground. And this has real consequences, because a wire in a moist environment with a reasonably low resistance to ground (say a nail in a bit of wet wood) with +9V on it will corrode, but a nail with -9V will not.
westaust55
Moderator
Even with a straight length of wire, the DC and AC resistance will differ.
That is due to skin effect with AC, where the current density is greater near the surface and little current flows near the centre of the conductor.
Then as mentioned inductance/capacitance will come into play with AC measurements
That is due to skin effect with AC, where the current density is greater near the surface and little current flows near the centre of the conductor.
Then as mentioned inductance/capacitance will come into play with AC measurements
Jeremy Leach
Senior Member
I googled Impudance by mistake - which is an "Improvised Explosive Curry" according to the online Urban Dictionary....
BeanieBots
Moderator
I thought that was not being able to reach your full potential.
Jeremy Leach
Senior Member
Correct, as explained here .. http://en.wikipedia.org/wiki/The_Answer_to_Life,_the_Universe,_and_Everything#Answer_to_Life.2C_the_Universe.2C_and_Everything_.2842.29
All picaxe related (!) but digressing a bit