Frequency and Basic Circuits

Discussion in 'General Electronics Chat' started by rperea, Apr 21, 2009.

Apr 7, 2009
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I have another queation to be discussed.....sometime I get confuse whenever they try to find some electrical properties and they use frequency as a factor. Is this because they are using AC circuits and they focus their attention on the current or voltage frequency? What about DC components, does frequency matter?

For example.....if I want to find the conductivity of a material...they i found sources where frequency is a variable that change its value or maybe the dielectric or the capacitance, etc....

Apr 7, 2009
15
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I am asking this because I find many articles that have this kind of expression:

"The permittivity of bone reaches very high
values at low frequencies, but decreases rapidly with increasing fre-
quencies and approaches a limiting value of about ten...."

3. steinar96 Active Member

Apr 18, 2009
239
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Frequency affects various components in circuits. For example as the frequency increases in a circuit the impedance of a capacitor decreases. Likewise the impedance of a inductor increases.

And yes frequency is mostly used when dealing with AC circuits.

4. KL7AJ AAC Fanatic!

Nov 4, 2008
2,181
410
Yes, dielectric constant and dielectric absorption are frequency dependent parameters. (They are actually defined by a complex number)

This becomes particularly crucial at microwave frequencies! Materials with very similar breakdown voltages, for example, teflon and vinyl, behave very differently. You can stick teflon in a microwave oven and nothing happens...stick a piece of vinyl electrical tape in there, and it basically evaporates!

Eric

5. Wendy Moderator

Mar 24, 2008
21,439
2,958
Not meaning to hijack this thread, but vinyl absorbs microwaves? I know water ice is transparant to them, while water absorbs them and is heated because of it.

To answer the OP question, DC is not a frequency, or to put it another way, it is 0 Hz.

6. Salgat Active Member

Dec 23, 2006
215
1
AC current is able to pass through capacitors. The resistance of capacitors and inductors is based on their inductance/capacitance and the frequency. This "AC resistance" is also known as impedance. Capacitors are highly resistive to low frequencies but easily pass high frequencies, while Inductors are highly resistive to high frequencies but easily pass low frequencies.