• Electro_vass
In summary, the voltage across the resonant LC circuit is approximately the same at all frequencies. However, the time it takes for the capacitor to charge affects the output voltage.
Electro_vass
Hi,

Im quite new to frequency and how it effects a circuit with both capacitors and inductor. I have created a simple circuit in Multisim and run an AC-analysis.
Pictures of both circuit and analysis is attachments.

What is happening here.

And arent the circuit also depending on the time (When the capacitors is getting fully charged)?

What I think is happening;

1. With lov frequency both the capacitor will have very high resistance, and the inductor will have very lov. Because of JWL, and 1/Jwl W= rad/s
And all the voltage will be the same, because now current will run tru the circuit.

2. Then with higher frequency the capacitors will start charging, and therefore it will take som voltage.

But is it not time depending, only frequency depending?

I am not quite sure what your problem is - however, you must strictly discriminate between analyses in the TIME and FREQUENCY domain.
You have performed an AC analysis (frequency domain) and, therefore, you cannot expect to see any time dependence in the simulation result.
Your output voltage is measured across a series LC resonant block which has an impedance minimum (zero) at the resonant frequency.
As a consequence, the output voltage goes down to zero at this frequency.
Very far below and above this frequency either the capacitor or the inductor, respectively, provide a very large impedance - hence, the complex impedance divider between R and the LC block exhibits (nearly) no damping and the output approaches "1".
Please note that it is common practice to display such results using logarithmic units (dB).
In case you want to study the time behaviour of the circuit you have two choices (TRAN analysis):
* Response to a voltage step at the input,
* Response to a sinusoidal signal (fixed frequency) .

Electro_vass said:
Im quite new to frequency and how it effects a circuit with both capacitors and inductor. I have created a simple circuit in Multisim and run an AC-analysis.

Theory in this case is the application of the phasors in a steady state AC circuits analysis.
How quickly will you learn this depends on the math background you have.
http://www.ece.msstate.edu/~donohoe/ece3183ac_analysis.pdf

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jim hardy
LvW said:
I am not quite sure what your problem is - however, you must strictly discriminate between analyses in the TIME and FREQUENCY domain.
You have performed an AC analysis (frequency domain) and, therefore, you cannot expect to see any time dependence in the simulation result.
Your output voltage is measured across a series LC resonant block which has an impedance minimum (zero) at the resonant frequency.
As a consequence, the output voltage goes down to zero at this frequency.
Very far below and above this frequency either the capacitor or the inductor, respectively, provide a very large impedance - hence, the complex impedance divider between R and the LC block exhibits (nearly) no damping and the output approaches "1".
Please note that it is common practice to display such results using logarithmic units (dB).
In case you want to study the time behaviour of the circuit you have two choices (TRAN analysis):
* Response to a voltage step at the input,
* Response to a sinusoidal signal (fixed frequency) .
Thanks a lot for the response. I now understand much better. Do you know why its common pratice to display results using logarithmic units (db9?

zoki85 said:
Theory in this case is the application of the phasors in a steady state AC circuits analysis.
How quickly will you learn this depends on the math background you have.
http://www.ece.msstate.edu/~donohoe/ece3183ac_analysis.pdf
Thanks. I will read the PDF. I have learn some stedy state before, but its getting more complex now, with different frequency. I am sure its a good ide to read it over again then.

Last edited by a moderator:
Electro_vass said:
Do you know why its common pratice to display results using logarithmic units (db9?

Your question concerns the so called BODE diagram. Here, the magnitude is displayed in dB and the phase in deg - both over a log. spaced frequency axis.
This has many advantages. One adavantage is that it is very easy to verify the relation between amplitude (magnitude) and phase. I recommend to read some book chapters or other contributions using the keyword "Bode diagram".

Electro_vass said:
Do you know why its common pratice to display results using logarithmic units (db9?
The main reason for using a dB scale is that you can cover a huge range of values. This is along the same lines as the use of 'Standard Form' - e.g. 2.34 X1012, which avoids writing masses and masses of zeros (2340000000000). The dB scale is similarly based on the base ten logarithm of a number. Confusing until you get so used to it that you can't do without it.

Electro_vass
Electro_vass said:
Thanks. I will read the PDF. I have learn some stedy state before, but its getting more complex now, with different frequency. I am sure its a good ide to read it over again then.
the graph you have of Vout is the steady state magnitude and phase of the signal Vout in your circuit vs frequency. if you did a time analysis at various frequencies, you would find that there would be some delay before the outut mag and phase settled at their steady state value

that means that with a 1k frequency input, your output will be one value after some time. If you were to use a signal of a different frequency this value will be different.

Lets look at the circuit. at DC, current will not move through a capacitor, so it makes sense that Vout will equal the voltage input (zero current through the resistor, so zero voltage drop)
at daylight ("inf" frequency) current will not move through an inductor, so it makes sense that Vout will equal the voltage input (zero current through the resistor, so zero voltage drop)

sophiecentaur said:
The main reason for using a dB scale is that you can cover a huge range of values. This is along the same lines as the use of 'Standard Form' - e.g. 2.34 X1012, which avoids writing masses and masses of zeros (2340000000000). The dB scale is similarly based on the base ten logarithm of a number. Confusing until you get so used to it that you can't do without it.
Thanks for a very good explanation. That makes so much sense now
sophiecentaur said:
The main reason for using a dB scale is that you can cover a huge range of values. This is along the same lines as the use of 'Standard Form' - e.g. 2.34 X1012, which avoids writing masses and masses of zeros (2340000000000). The dB scale is similarly based on the base ten logarithm of a number. Confusing until you get so used to it that you can't do without it.
Thanks for a good, simple explanation. That makes so more sense now.

## 1. What is frequency?

Frequency refers to the number of occurrences of a repeating event per unit of time. It is often measured in hertz (Hz), which represents the number of cycles per second.

## 2. How is frequency calculated?

To calculate frequency, divide the number of times an event occurs by the total time it takes for those occurrences. This will give you the frequency in units of hertz (Hz).

## 3. What is the relationship between frequency and wavelength?

Frequency and wavelength are inversely proportional to each other. This means that as frequency increases, wavelength decreases, and vice versa.

## 4. How does frequency affect sound and light?

In sound, frequency determines the pitch of the sound. Higher frequency sounds have a higher pitch, while lower frequency sounds have a lower pitch. In light, frequency determines the color of the light. Higher frequency light has a bluer color, while lower frequency light has a redder color.

## 5. How can frequency be changed?

Frequency can be changed by altering the speed of the event or by changing the medium through which the event passes. For example, in sound, frequency can be changed by changing the speed of the vibrations or by changing the density of the medium through which the sound travels.

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