# cutoff frequency of low pass filter

Discussion in 'Homework Help' started by rondo1994, May 1, 2014.

1. ### rondo1994 Thread Starter New Member

Apr 6, 2014
12
0
how do i determine the cutoff frequency of this circuit, the answer given is fc=4.226 Hz

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2. ### ericgibbs AAC Fanatic!

Jan 29, 2010
2,583
389
hi,
I guess you meant the title to be high pass filter.?

What do calculate the Low frequency -3dB point to be .?

E

3. ### rondo1994 Thread Starter New Member

Apr 6, 2014
12
0
Ya, high pass sorry about that.

Jan 29, 2010
2,583
389
no problem

5. ### rondo1994 Thread Starter New Member

Apr 6, 2014
12
0
Yes, i don't know how the resistor connected in parallel with the capacitor affects the value.

6. ### ericgibbs AAC Fanatic!

Jan 29, 2010
2,583
389
Do you know how to calculate the impedance Xc of the 10uF cap.?

7. ### rondo1994 Thread Starter New Member

Apr 6, 2014
12
0
yes 1/(2pifc)

8. ### ericgibbs AAC Fanatic!

Jan 29, 2010
2,583
389
Ok,
As this is homework I cannot give you the answer, but consider.

What the attenuation in the Output when the Freq=0 , also whats the attenuation when the Freq > 1000Hz.??

This should give you a clue that some value of Xc will give an attenuation of 0.5.

9. ### rondo1994 Thread Starter New Member

Apr 6, 2014
12
0
what does the resistor connector in parallel to the capacitor do then?

10. ### ericgibbs AAC Fanatic!

Jan 29, 2010
2,583
389
At Freq=0 the Xc is infinite, so the attenuation ratio from input to output is 1:0.5

At Freq > 1000Hz, the Xc can be assumed close to zero, so the attenuation ratio is 1:1

11. ### atferrari AAC Fanatic!

Jan 6, 2004
2,663
783
Hola Eric,

I am surprised I completely forgot how to suscribe to a thread (this one in particular now) other than posting in it. (?)

12. ### ericgibbs AAC Fanatic!

Jan 29, 2010
2,583
389
Hola Agustin.
I am sorry I dont know.

Perhaps a Mod may point us both in the right direction.

Eric

13. ### rondo1994 Thread Starter New Member

Apr 6, 2014
12
0
Ok solved it using transfer function thx.

14. ### ericgibbs AAC Fanatic!

Jan 29, 2010
2,583
389
hi,
Could you post your calculations, it could help other students.

E

15. ### atferrari AAC Fanatic!

Jan 6, 2004
2,663
783
Hola rondo,

Out of curiosity I would like to see that!

Gracias.

16. ### anhnha Active Member

Apr 19, 2012
776
48
Hi.
You may try this.

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atferrari likes this.
17. ### atferrari AAC Fanatic!

Jan 6, 2004
2,663
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As usual, just in front of me.

Gracias!

18. ### jjw Member

Dec 24, 2013
174
31
3dB point is at 1/sqrt(2) ~ 0.707

19. ### jjw Member

Dec 24, 2013
174
31
Did you get the same answer 4.226 Hz as in your first message?