I applied 120 volts rms. And I measured rms voltages across each component.

Umm, thats weird. Are you sure you don't have dependant sources in your circuit?

120V rms meaning from the wall outlet? Power from the wall is really weird anyway and does some strange things.

I would rather use a function generator where I know I have only single phase power and no weird stuff.

 

120 volts AC at 60 hertz applied to a 1,000 mFd capacitor, 1.6 ohm resistor, 50 millihenry coil.

I see 12 volts across the resistor.
I see 20 volts across the capacitor.
I see 140 volts across the inductor.

My meter is only accurate to 5% but this IS what I have.

The secret is in the timing!

 

120 volts AC at 60 hertz applied to a 1,000 mFd capacitor, 1.6 ohm resistor, 50 millihenry coil.

I see 12 volts across the resistor.
I see 20 volts across the capacitor.
I see 140 volts across the inductor.

My meter is only accurate to 5% but this IS what I have.

The secret is in the timing!

That is especially weird because at low frequencies like 60hz the inductor acts like a short circuit. The voltage across it should be low. The highest voltage should be across the capacitor. This is basically a bandpass filter.

Is the secret in the phase angles?

 

Yes, it is. The meter shows RMS not instantaneous voltage.

There is a phase difference between the voltage across the capacitor and inductor (and the resistor). If you could measure the voltages across each part at the same INSTANT, the voltages would all add up to 120.

But an RMS meter sure could not do that.

 

Whoa hold on a minute. This is pretty interesting and relevant to what I'm doing now. We are doing a filter lab right now, and one of the circuits to test was an RLC circuit like this.

We were using labview to get voltages across components at a range of frequencies from 10-10000Hz. I don't seem to remember a result like this. Then again labview does all this automatically and perhaps does measure everything at the same instant. It uses a multimeter and displays RMS voltages too.

Can you explain why this happens in more detail? I will have to check it out and try it!

 

Remember ICE and ELI.

The current (I) leads the voltage (E) in a capacitive (C) circuit.
and..
The Voltage (E) leads the current (I) in an inductive (L) circuit.

I am surprised you have not had this. You should not be working with filter circuits unless you have had an intro to capacitors and capacitive reactance and inductors and inductive reactance.

Let me go looking for links...

 

This is an online calculator, but it doesn't teach very well.

http://www.ngsir.netfirms.com/englishhtm/RLC.htm

You can play around with values and get an idea of what is going on.
But it still BUGS me that you are working on filter circuits and have not had AC component theory. I am not impressed by the way your classes have been laid out!

 

Remember ICE and ELI.

The current (I) leads the voltage (E) in a capacitive (C) circuit.
and..
The Voltage (E) leads the current (I) in an inductive (L) circuit.

I am surprised you have not had this. You should not be working with filter circuits unless you have had an intro to capacitors and capacitive reactance and inductors and inductive reactance.

Let me go looking for links...

No no, I had ICE and ELI. I know it. I just forgot. Maybe I never paid attention to this. Now that I did think about it, I think I get it.

I mean you know, when I was calculating voltages and currents and saw that they all have different phase angles, I thought "okay thats nice" but never thought about what it actually means if you try to measure them with a multimeter.

They don't emphasize the importance of phase angles enough in our classes, maybe thats a problem, but its not like nobody told us about them.

I know that capacitors have reactance due to their ability to store charge, and inductors due to their building and collapsing magnetic fields. And a general way to describe this is using impedance with complex numbers.

My classes really arnt that bad LOL.

Thanks. This is very interesting. Will have to check it out in lab tommorow.

 

You will have a lot of fun with the math, I can tell.

The whole "phase angle" is fun theory, but it is ALSO real. I had a lot of fun playing with a resistor, capacitor and inductor in lab - driving them in series at various frequencies.

But first, grab a resistor and capacitor, place them in series, and work out the math to predict what you should see. THEN, turn the generator on and see how close the math is!

It seems like super-simple stuff, but it IS important. It is also fun to "break the rules" or at least LOOK like you are breaking the rules (as in this thread).

THEN, you get to break another rule, when you get to playing with RF. 'Cause with RF, you get to make current flow in open circuits!

 

You will have a lot of fun with the math, I can tell.

The whole "phase angle" is fun theory, but it is ALSO real. I had a lot of fun playing with a resistor, capacitor and inductor in lab - driving them in series at various frequencies.

But first, grab a resistor and capacitor, place them in series, and work out the math to predict what you should see. THEN, turn the generator on and see how close the math is!

It seems like super-simple stuff, but it IS important.

When I get home from work I will work out the math for your circuit. I have to see this to believe this you know. Phase angles are pretty cool.

After all, (sound + sound 180 degrees out of phase) = silence

 

After all, (sound + sound 180 degrees out of phase) = silence

THey use that to cancel sound in some headsets, you know. (ACTUAL noise-cancelling headsets, unlike the old "noise cancelling" microphones that didn't really CANCEL noise.)

 

Its awesome that you are trying to jump ahead so fast but anything with inductors and capacitors will be hard to you without calculus, and all filters have those even if with an op amp.

Hi count_volta,

I know this thread is about done to death and way off original post but it makes interesting reading .....

You can easily solve both steady state and transient circuit theory problems involving inductors and capacitors without resorting to the calculus. I guess you are making the point that differential calculus underpins the methods we employ to solve such problems.

If I was studying an electrical trades course for instance, I may still be taught the methods of AC circuit theory solution without ever having done calculus.

Rgds,

t_n_k

 

Hi count_volta,

I know this thread is about done to death and way off original post but it makes interesting reading .....

You can easily solve both steady state and transient circuit theory problems involving inductors and capacitors without resorting to the calculus. I guess you are making the point that differential calculus underpins the methods we employ to solve such problems.

If I was studying an electrical trades course for instance, I may still be taught the methods of AC circuit theory solution without ever having done calculus.

Rgds,

t_n_k

Well sure, imaginary numbers arn't really calculus. But Electronerd is a freshman in high school and didnt even have those yet.

But any Laplace type of thing you really should know calculus, or else you arn't learning correctly.

 

Well sure, imaginary numbers arn't really calculus. But Electronerd is a freshman in high school and didnt even have those yet.

But any Laplace type of thing you really should know calculus, or else you arn't learning correctly.

Awww...man! Ya have to tell all my secrets!?

 

Actually what t_n_k is saying is that first you should learn the concepts using the simplest math techniques. Then, if it's necessary you can use calculus; but only when it's necessary!

Is that right t_n_k?

 

Actually what t_n_k is saying is that first you should learn the concepts using the simplest math techniques. Then, if it's necessary you can use calculus; but only when it's necessary!

Is that right t_n_k?

Hi ELECTRONERD,

Indeed that's the point. If we had to solve everything using calculus directly, then it would be even more laborious than it already is.

Mind you, without a reasonable mathematical / physical grasp of the concepts we use to model circuit behavior it might be harder for us to experience those unfortunately rare "Aha!" moments that come our way. Such as when we are able to explain why the voltage across a component in a passive circuit is greater than the applied source voltage.

Rgds,

t_n_k

 

Thanks t_n_k, I'll keep that in mind.