# Impedance Diagram of Low Pass Filter

I am to draw an impedance diagram of a low pass filter and indicate the phase angle. Is the phase angle found by: 1) -arctan(?RC)
or 2) -arctan(Xc/R)
Appreciate if someone could advise which one of the above is correct.
TIA
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>

Have you thought of trying a textbook?
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
John Nice wrote:

What are we charging for homework answers these days?
--
Paul Hovnanian mailto: snipped-for-privacy@Hovnanian.com
------------------------------------------------------------------
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
A simple answer 1 or 2 would be fine, the notes we have been handed says to use -arctan(wRC), however, I was unsure of this thinking back to my old ac theory days. I came over an article on the net which says to use -arctan(Xc/R). There are a lot of other questions associated with this question, I will work everything out. All I need to know is which formula is correct. Or don't you know? Maybe I should ask elsewhere. TIA

<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
On 11/9/06 9:51 PM, in article 455413d3\$0\$18045\$ snipped-for-privacy@news.zen.co.uk,

I do not think you should ask anyone. You should not bother anyone. Presumably you know what frequency, resistance, and capacitance are. If you do not know how to calculate lag angles of SIMPLE RLC combinations of components, you are not ready to ask your question. And if you do know how to make such calculations, there would be no need to ask the question.
So my clue is: The answer is easy if you know what you are doing.
Bill -- Fermez le Bush
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Salmon Egg wrote:

I found it a little more worrying that they don't seem to be teaching reduction of the units expressed within equations. eg If someone needs something to be a ratio and it reduces to a value in volts, they have got the equation wrong...
--
Sue

<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Palindr?me wrote:

That's what happened when everyone started using calculators instead of slide rules! :-)
--
Virg Wall, K6EVE

<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>

No, I learned it just fine with a calculator in 1977-1982. Pick another reason.
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>

I know I'll "stir up a hornet's nest" with this, but I think it's been the conversion to the metric system. Here's why. In the old 'English' system, one thing you always had to do is express the answer in the requested units. So part of learning how to do all sorts of calculations is how to carry the units with each item, and conversions from one form of units to another. With the odd/awkward units of the 'English' system ( ft-lbf, hp, BTU, etc...), we just naturally learned to always carry the units along with each item. So we had to learn all those darn conversions :-(. But we also learned to keep track of units and dimensions (length, time, energy, etc...) :-)
With the metric system, quite often you can 'get the right answer' without keeping track of units, simply because most of the conversions are a factor of '1'. Take 12 Newtons, through a distance of 5 meters, how many Joules?? Nowadays, someone is just as likely to say "12*5`" instead of "12N * 5m * (1 J / N-m) = 60 J".
But in "English", take 12 lbf through a distance of 15 ft, how many BTU??? (12lbf * 15ft) * (1BTU / 778 ft-lbf) = 0.231 BTU. You just *have* to keep track of units in order to know what conversions need to be applied.
Now, I like the metric system as much as the next person. It *is* easier to work many things with it. But I still carry all the 'units' through, just because "that's the way I learnt it".
As for the OP, trying to take the arctan of something, the 'something' has to be a dimensionless number. R*C would give you units of ohms-Farads, there is no way to take the arctan(ohm-Farad). Think about it some more, and you'll see the answer.
daestrom
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>

-------------------------- but it was the arctan of wRC which, correct or not ( arctan 1/RwC appears better), is unitless
--

Don Kelly snipped-for-privacy@shawcross.ca
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
wrote:

Ah yes. "Unit analysis" was actually taught as a course for half semester in "my day". By tagging the units on to every thing, and knowing what items were ratios or 'pure numbers', we could cancel out the various units and figure out the necessary conversions.
daestrom
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Hi! Please check out www.eehomework.com for some neat tips for all your electrical engineering problems.
John Nice wrote:

<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>

-----------------
The phase angle depends on the frequency. IF, as you have not indicated, you are looking for a half power point, there are specific expressions which can easily be worked out. Your question is somewhat vague. I would suggest that you do your homework as asked. This might require some effort on your part but it is worthwhile doing.
--

Don Kelly snipped-for-privacy@shawcross.ca