Capacitors & Capacitance

[Jamie]

Hi,
Just been reading about capacitors and understand the property of
capacitance. The problem is I don't see how this property is of use, many
circuits use capacitors but I don't understand what there role is.

I know capacitors don't allow current to flow through them and that they can
be charged and discharged and that the time taken to charge and dischage can
be calculated. But how are these devices off any real use?

Thanks for ya time guys.

let me give you an example.
lets assume that you have the need for a negative pulse from a circuit
that only has a common and + supply of voltage.
using a 100Uf capacitor to test with, connect the - side to your +
input of your DM ( multimeter Voltage Scale). the - lead of your DM to
the common side of lets say a 9 volt battery which would be the -
terminal in this example.
using a simple thing like a double throw switch, connect the + side
of the capacitor to the center pole of the switch, one side of the switch
to common and the other side to the + terminal on the 9 v battery.
watch you DM as you switch from one side to the other.
you will noticed that you get a momentary pulse of + voltage when the
center pole of the switch is connected to the + terminal of the Battery.
now switching the center pole of the switch to the common side (which
would be the - side of your battery) yields a - voltage in your meter.
if you were to short the capacitor with a jumper and repeat the action
of connecting the center pole of the switch to + terminal of the battery
and then the common side (- terminal of the batter), you will see only a
+ reading on your meter and then only a 0 zero, you will not see a -
voltage develop.
just think of a battery's terminals being switched to give reverse
polarity.
the capacitor is in effect a cell (battery being 2 or more cells);
--
now lets apply this to a simple class A amplifier.
i will only talk about the basics here.
imagen using a resistor from the + terminal of your 9 volt battery to
supply current to the collector of a transistor.
now when the circuit is properly biasing the transistor (setting is
current state), you can measure the voltage at the collector and lets
assume that it is for now 50% of the supply voltage, in this case
using your 9 volt batter = 4.5 volts.
if you were to connect a speaker to this same point, the speak would
push to one side and stay there due to the DC , there for you would only
get a half cycle movement in the speaker. this is not good.
if you were to now decouple the connection with a capacitor of lets
say around 1000 uf or more (incase you want to experiment with this),
the variation of voltage at the collector and resistor will give you a
+ and - (true -) voltages. When the DC stabilizes, the cap will become
fully charged and thus no current will no longer flow leaving the
speaker cone at it's natural resting place.
So you can simply think of capacitors in circuits like alternate the
direction of flow to give you real AC voltage effects, and
also caps are used to suppress the variations voltages and for making
time constant effect circuits etc. ( the list goes on)
if you would look at a LM555 timer and some examples, you could a
good idea how they could be applied in timers, oscillators (tone
generators) etc.
you mite want to get your hands on one of those 101 kits. they are
very intuitive for introducing people to electronics.

I hope long winded message didn't bore you.

 

[Kitchen Man]

Hi,
Just been reading about capacitors and understand the property of
capacitance. The problem is I don't see how this property is of use, many
circuits use capacitors but I don't understand what there role is.

I know capacitors don't allow current to flow through them and that they can
be charged and discharged and that the time taken to charge and dischage can
be calculated. But how are these devices off any real use?

Thanks for ya time guys.

You said it: "Time taken to charge and discharge can be calculated."
This allows us to use fancy math to make electrons dance any dance we
want, from pulling the buzz out of electricity that we want to be clean,
to putting the zing into electricity that we want to resonate - for
instance, creating a musical note in an electric piano. IOW, caps allow
us to remove and create frequencies accurately and reliably. This puts
music and speech on top of radio waves, alphabetic characters on a video
screen, and squeezes wall-shaking rumbles out of subwoofers.

You may have misread that documentation you have that says capacitors do
not pass AC. That's kind of generally what happens, but what your book
most likely means is that capacitors give us the means to control what
frequencies of AC are allowed, and which are not.

 

[Ross Mac]

Since pure DC has no rate of change, it produces no current through a
capacitor. but any other voltage waveform from varying DC to
sinusoidal AC or any other variation in voltage over time causes
current to pass through capacitors.

And so explaining the old term "Blocking Condensor"....
Great explanation John, as usual!.........Ross

 

[Mike Webster]

There is a diagram over these factors which I think is very useful
but I can only find it in a pdf file from a swedish company.
http://www.elfa.se/se/fakta.pdf

I wish there was a better way to find such a diagram, better than
to have to download a pdf file in swedish and find the diagram. If
anybody knows about such diagrams in other places on the web, tell
us about it.

These diagrams are useful because you only need your eyes to focus
and follow lines, there is no need to do calculations or touch
anything, I have this diagram in front of me all the time at the
work bench, and use it very often.

Is it anything like the Smith chart listed here: ?
http://dbserv.maxim-ic.com/appnotes.cfm/appnote_number/742

About halfway down, the blown up version, unfortunately, has writing on
it.

Ah, sweet Google to the rescue, check here:
http://www.sss-mag.com/smith.html

BTW, This group has instantly restored my faith in Usenet after
languishing for years in the alt. domains ...

Mike Webster
Sophomore, ECE, NCSU

 

[Roger Johansson]

The diagram for calculating relations between voltage, resistance,
current and power (wattage) in a linear (ohmic) resistance:

http://humanist.250free.com/VAOW2.jpg

If you know the voltage and the resistance of a resistor you follow the
line from the voltage scale and the line from the resistance scale to the
point where they meet. From that point go to the other scales and you see
the current and the wattage (power) on the other scales.

Use a pen to point at the meeting point in the beginning, later it is
easy to just focus your eyes on a certain point. Very handy when your
hands are occupied with a soldering iron and components.

I have added some colors to the diagonal resistance scale which are the
third ring color on resistors, and I have extended the diagram upwards to
calculate higher currents than the original diagram.

Sorry about the messy look but I have used this for many years and added
lines as I needed it. I used a scanner to get it off the front cover of
my homemade workbench handbook. I would love to see a better version of
the diagram.

.......

The diagram for calculating inductance, capacitance, impedance and
frequency:

http://humanist.250free.com/LCFO2.jpg

This is also very useful for calculation of resonance frequency in LC
circuits, see where the L-value and the C-value meet, and see what
frequency that gives.

Is it anything like the Smith chart listed here: ?
http://www.sss-mag.com/smith.html

It works in the same way, it gives a simple visual graphic solution
instead of using equations and a calculator.

BTW, This group has instantly restored my faith in Usenet after
languishing for years in the alt. domains ...

There are more groups which are very helpful and relatively nice, try
alt.comp.freeware for discussions and announcements of free software for
all your needs. The participators in a.c.f vote for the best freeware in
all categories every year, so you can easily find the best free software
for any purpose.

http://pricelesswarehome.org/

This year's list, divided into categories:
http://pricelesswarehome.org/2005/about2005PL.php

 

[Roger Johansson]

The diagram for calculating relations between voltage, resistance,
current and power (wattage) in a linear (ohmic) resistance:
http://humanist.250free.com/VAOW2.jpg
The diagram for calculating inductance, capacitance, impedance and
frequency:
http://humanist.250free.com/LCFO2.jpg

In the angloamerican world it is seen as some kind of cheating to use
diagrams, they want people to memorize a lot of formulas instead.

In Europe (Germany) it is much more accepted to use diagrams. The first
diagram above is actually copied from a german book originally.
They use diagrams for many types of calculations.

I read an article in Wireless World many years ago about english and
american engineers visiting an electronics congress in Germany, and the
article made fun of the way german engineers always had a pocket book
(Schlau Buch = Sly Book = Handbook) with them and how they looked up
things instead of having everything memorized in their brains as the
angloamericans tried to do.

It has been an ideological difference in the way we teach and learn
things.

The germans think more like this; If we simplify everything as much as
possible we can free more energy and time to learn even more instead of
wasting our time with remembering equations, and making calculations with
pen and paper.

The british always want to do things "the right way", learning the proper
equations and doing the math. And american like to memorize things, even
when it fills no sensible practical purpose, like learning strange
sentences to remember the colors in the resistor color code.


I have tried to create better looking versions of these diagrams, using a
graph paper design program which could create logaritmic scales
vertically and horisontally. Then I took a copy of that diagram into a
paint program, rotated it 45 degrees and tried to superimpose it on the
original diagram, to create logaritmic scales diagonally as well as
vertically and horisontally.

But it didn't work so well, the program didn't produce diagrams which
were suitable for this. So I'll wait for better graph paper design
programs, or hope somebody else will create such diagrams.

You are free to copy and distribute these diagrams as you like, I cannot
keep them on a free web site indefinitely. Such web sites are often
closed down unexpectedly.

 

[John Fields]

In the angloamerican world it is seen as some kind of cheating to use
diagrams, they want people to memorize a lot of formulas instead.

In Europe (Germany) it is much more accepted to use diagrams. The first
diagram above is actually copied from a german book originally.
They use diagrams for many types of calculations.

I read an article in Wireless World many years ago about english and
american engineers visiting an electronics congress in Germany, and the
article made fun of the way german engineers always had a pocket book
(Schlau Buch = Sly Book = Handbook) with them and how they looked up
things instead of having everything memorized in their brains as the
angloamericans tried to do.

It has been an ideological difference in the way we teach and learn
things.

The germans think more like this; If we simplify everything as much as
possible we can free more energy and time to learn even more instead of
wasting our time with remembering equations, and making calculations with
pen and paper.

The british always want to do things "the right way", learning the proper
equations and doing the math. And american like to memorize things, even
when it fills no sensible practical purpose, like learning strange
sentences to remember the colors in the resistor color code.


I have tried to create better looking versions of these diagrams, using a
graph paper design program which could create logaritmic scales
vertically and horisontally. Then I took a copy of that diagram into a
paint program, rotated it 45 degrees and tried to superimpose it on the
original diagram, to create logaritmic scales diagonally as well as
vertically and horisontally.

But it didn't work so well, the program didn't produce diagrams which
were suitable for this. So I'll wait for better graph paper design
programs, or hope somebody else will create such diagrams.

You are free to copy and distribute these diagrams as you like, I cannot
keep them on a free web site indefinitely. Such web sites are often
closed down unexpectedly.

 

[Roger Johansson]

And handbooks can be lost, or stolen, or destroyed, but having once
heard "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx foul language", it's
with you for life.

As others have already pointed out this introduces an unnecessary step in
the thinking process. It is a lot easier to learn to associate the color
with a number directly.

The best way to learn the colors is to sort a few hundred mixed resistors
using a color code table.

After that you need only look at that table occasionally to reinforce the
color you are not sure about.

How do you learn the multiplication table in your schools?

Do you have some foul language mnemonic sentences for that too?

And what happens if you see a few movies from Hollywood filled with more
extreme foul language wordings which I will not exemplify here.

Do you get your colors codes and multiplication tables all mixed up then?

I am pretty sure you don't even use such mnemonics yourself when you look
at a resistor. You associate the color with a number directly, don't you?

 

[John Fields]

As others have already pointed out this introduces an unnecessary step in
the thinking process. It is a lot easier to learn to associate the color
with a number directly.

---
Bullshit. It's an index which co-relates a number and a color with a
"naughty" phrase.
---

The best way to learn the colors is to sort a few hundred mixed resistors
using a color code table.

---
For you, maybe. For someone else, maybe not.
---

After that you need only look at that table occasionally to reinforce the
color you are not sure about.

---
I learned them by memorizing them, and I suspect that's how it's still
done, although maybe we've gone the German route and all the little
kids carry handbooks around so they don't have to clutter up their
minds with all that memorized garbage.
---

Do you have some foul language mnemonic sentences for that too?

And what happens if you see a few movies from Hollywood filled with more
extreme foul language wordings which I will not exemplify here.

Do you get your colors codes and multiplication tables all mixed up then?

 

[Rikard Bosnjakovic]

http://humanist.250free.com/VAOW2.jpg

"Hotlinking not permitted".


--
Rikard Bosnjakovic http://bos.hack.org/cv/

Anyone sending unwanted advertising e-mail to my address will be
charged $250 for network traffic and computing time. By extracting
address from this message or its header, you agree to these terms.

 

[c_t]

I personally have grown weary of how electronics is taught in America. I
wanted to see your diagrams, but it said that there is no Hotlinking,
(whatever that is), and to visit the site directly.

Can you help me out?

Thanks,

 

[Rich Grise]

I learned them by memorizing them, and I suspect that's how it's still
done, although maybe we've gone the German route and all the little
kids carry handbooks around so they don't have to clutter up their
minds with all that memorized garbage.

Nah. Pocket calculators. And then when they go to work, they only
have to press the buttons with the pictures of the burgers and fries,
and the POS terminal does all of the math for them.

Thanks,
Rich

 

[Roger Johansson]

wanted to see your diagrams, but it said that there is no Hotlinking,
(whatever that is), and to visit the site directly.

Can you help me out?

Ooops, sorry.

I had no problems clicking on the links I gave you, so I thought it would
work for others too, but now I realize they have put a cookie on my
computer so they know I am the owner, so I am allowed to go to the
picture directly.

For them to be available for other people I had to re-edit my index.html,
and I have done that now. I hope it will work now.

Try this link http://humanist.250free.com/

Then click on the two .jpg files at the bottom of the list.

Please tell me if it doesn't work, 'cause I want them to be available to
you and others.

 

[Roger Johansson]

And handbooks can be lost, or stolen, or destroyed..

Cool!

 

[Roger Johansson]

"Hotlinking not permitted".

For them to be available for other people I had to re-edit my index.html,
and I have done that now. I hope it will work now.

Try this link http://humanist.250free.com/

Then click on the two .jpg files at the bottom of the list.

Please tell me if it doesn't work, 'cause I want them to be available to
you and others.