Do capacitors allow or block ac signals?

[ameet]

Now that I have heard that capacitors "allow" ac signals but "block"
dc signals as below.

Xc=1/[2(pi)(Fc)],

Fc=frequency of signal.

Now for dc signals Fc=0 Hz sothat Xc~infinity which implies that it is
open circuited,so we conclude that capacitor blocks dc signals and
allows ac signals(as they have a definite value of Fc).


But the problem is here: Why do we use capacitors in radio circuits to
"block" noise signals which are nothing but ac signals?????

Can any one please explain where I am going wrong?????

 

[UncleWobbly]

it depends on the application:

A capacitor between a signal line and 0V will reduce any AC present - in the
same manner as smoothing caps in a main power supply.

Capacitors in series, i.e. cut the signal line and insert a capacitor, will
block DC as you have proved mathematically below, the AC will be affected by
the same equation so if you wish to pass a signal but block others (a simple
'band pass') you will need the right cap for the right job, smaller caps
will pass higher frquency signals... and vice versa.



"ameet" <ameet321@yahoo.com> wrote in message
news:e6f52e9d.0311150119.2d68f09d@posting.google.com...

Now that I have heard that capacitors "allow" ac signals but "block"
dc signals as below.

Xc=1/[2(pi)(Fc)],

Fc=frequency of signal.

Now for dc signals Fc=0 Hz sothat Xc~infinity which implies that it is
open circuited,so we conclude that capacitor blocks dc signals and
allows ac signals(as they have a definite value of Fc).


But the problem is here: Why do we use capacitors in radio circuits to
"block" noise signals which are nothing but ac signals?????

Can any one please explain where I am going wrong?????

 

[Spudley]

A capacitor acts like a short circuit to ac, depending on the
frequency of the ac signal and the value of the capacitor, therefore
noise can be short circuited to ground with this characteristic, thus
reducing it's noisy effect on the rest of the circuit. At the same
time allowing the DC component within the signal to remain unaffected.

"ameet" <ameet321@yahoo.com> wrote in message
news:e6f52e9d.0311150119.2d68f09d@posting.google.com...

Now that I have heard that capacitors "allow" ac signals but "block"
dc signals as below.

Xc=1/[2(pi)(Fc)],

Fc=frequency of signal.

Now for dc signals Fc=0 Hz sothat Xc~infinity which implies that it
is
open circuited,so we conclude that capacitor blocks dc signals and
allows ac signals(as they have a definite value of Fc).


But the problem is here: Why do we use capacitors in radio circuits
to
"block" noise signals which are nothing but ac signals?????

Can any one please explain where I am going wrong?????

 

[DHB]

ameet,
I understand your question but from a purely technical point
your accretion that ("capacitors "allow" ac signals but "block"
dc signals" is incorrect). Capacitors appear to act in this manor but at an
engineering level however only a very tiny "leakage currant" actually passes
through the dielectric of a capacitor. If anything more were to pass
through it the dialectic insulator would be destroyed & the capacitor would
electrically short & them possibly become open or even explode depending on
how much energy was in the circuit.

Yes this is more technical than your question but I have always been 1
who questioned everything & I challenged my electronics teacher about this
since it did not fit my fundamental understanding of capacitor construction.
(Yes I asked him this after class) & he explained that my understanding was
in fact correct but that of practical reasons, in order to understand &
calculate how a capacitor works in a circuit this basic "capacitors "allow"
ac signals but "block"
dc signals" concept would need to be accepted as true.

It's always be interesting to me to learn why & where the "exceptions to
the rules" come from, some are required in order to simplify our basic
understandings of things. Electronics is much like pealing back layers of
an onion but yet you never seem to reach the center, at least that's how it
seems to me. I'm just a retired ET so my knowledge is limited but I try to
learn something new in this field everyday.

Respectfully, DHB

"ameet" <ameet321@yahoo.com> wrote in message
news:e6f52e9d.0311150119.2d68f09d@posting.google.com...

Now that I have heard that capacitors "allow" ac signals but "block"
dc signals as below.

Xc=1/[2(pi)(Fc)],

Fc=frequency of signal.

Now for dc signals Fc=0 Hz sothat Xc~infinity which implies that it is
open circuited,so we conclude that capacitor blocks dc signals and
allows ac signals(as they have a definite value of Fc).


But the problem is here: Why do we use capacitors in radio circuits to
"block" noise signals which are nothing but ac signals?????

Can any one please explain where I am going wrong?????

 

[Spudley]

"DHB" <yoda2k@verizon.net> wrote in message
news:GDVvb.5936$yy5.1428@nwrdny01.gnilink.net...

ameet,
I understand your question but from a purely technical
point
your accretion that ("capacitors "allow" ac signals but "block"
dc signals" is incorrect). Capacitors appear to act in this manor
but at an
engineering level however only a very tiny "leakage currant"
actually passes
through the dielectric of a capacitor. If anything more were to
pass
through it the dialectic insulator would be destroyed & the
capacitor would
electrically short & them possibly become open or even explode
depending on
how much energy was in the circuit.

Like any device in an electrical circuit, it has resistance.
All be it very high, this resistance varies between types of
capacitors and value of same.
The dielectric is effectively an insulator, it's purpose is to
separate the conductive plates of the capacitor.
In a perfect world it would be a perfect insulator with infinite
resistance, unfortunately that is not the case.
So electrically it does poses resistance and hence minute DC current
will flow through it.

Yes this is more technical than your question but I have always
been 1
who questioned everything & I challenged my electronics teacher
about this
since it did not fit my fundamental understanding of capacitor
construction.
(Yes I asked him this after class) & he explained that my
understanding was
in fact correct but that of practical reasons, in order to
understand &
calculate how a capacitor works in a circuit this basic "capacitors
"allow"
ac signals but "block"
dc signals" concept would need to be accepted as true.

It's always be interesting to me to learn why & where the
"exceptions to
the rules" come from, some are required in order to simplify our
basic
understandings of things. Electronics is much like pealing back
layers of
an onion but yet you never seem to reach the center, at least that's
how it
seems to me. I'm just a retired ET so my knowledge is limited but I
try to
learn something new in this field everyday.

Respectfully, DHB

"ameet" <ameet321@yahoo.com> wrote in message
news:e6f52e9d.0311150119.2d68f09d@posting.google.com...
Now that I have heard that capacitors "allow" ac signals but
"block"
dc signals as below.

Xc=1/[2(pi)(Fc)],

Fc=frequency of signal.

Now for dc signals Fc=0 Hz sothat Xc~infinity which implies that
it is
open circuited,so we conclude that capacitor blocks dc signals and
allows ac signals(as they have a definite value of Fc).


But the problem is here: Why do we use capacitors in radio
circuits to
"block" noise signals which are nothing but ac signals?????

Can any one please explain where I am going wrong?????