# really need help with physics coursework

Discussion in 'Homework Help' started by mandy, Jul 21, 2010.

1. ### mandy Thread Starter New Member

Jul 21, 2010
2
0
hi
i have to produce a report on how to construct an electronic circuit.
i need to prouce a circuit made from a resistor of 1Ω and a capacitor, i need to produce a first order low pass filter with a fc of 2.5khz and a high pass filter with fc of 4khz. i also need to sketch the freq vs gain characteristics.
im not sure what equipmnt to use or how to set up the circuit, ive read through books but cant seem to get my head round it. can any1 help plz

2. ### Wendy Moderator

Mar 24, 2008
20,993
2,731
Do you know how to calculate reactance for a specific frequency and a specific value of capacitance?

Do you know how to calculate the total reactance of an RC circuit?

3. ### tubelite New Member

Jul 20, 2010
6
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hmmm, well people can give you the answer straight but part of the learning experience is reading and understanding... what portions of the reading do you not understand. From what i understand you need to produce

1. a circuit with a 1 ohm res and a cap
2. a first order low pass filter centered at 2.5khz
3. a first order high pass filter centered at 4khz
4. sketch of the freq vs gain

i'd recommend reading volume vi chapter 2 for help on how to connect circuits. By the way you need to make the time to read this material and be patient in order to understand it.

I hope that helps mandy and i'm always willing to help. Have a good time.

4. ### mandy Thread Starter New Member

Jul 21, 2010
2
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Thanks for replying. I have the formula to work it out.for the low pass filter i think its fc=1\(2*pi*r*c) which i think works out to 1\(2*pi*2500*1000) = 63.66nf. Im not sure about the highpass filter because i think the equation needs rearranging. I understand that part i think its just working out the gain. 20log10 vout\vin... Iv tried to work that out but it says error everytime.

As for the reading material you suggested. Is that on this site??

Im not sure how to construct the circuit and test for different freqs. Any hints or tips you can give me will be much appreciated. I love learnibg about physics but i just cant seem to understand it..if that makes sense

thanks
mandy

5. ### Georacer Moderator

Nov 25, 2009
5,151
1,266
The knee frequency of the high pass filter is the same as the fc of the low pass. But instead of loosing gain at that frequency, the high-pass filter reaches its maximum. Refer to http://www.electronics-tutorials.ws/filter/filter_2.html, pages 2 and 3. I 'm really sorry that I didn't post a link to the e-book or Wikipedia, but neither has the formulas clean and simple along with the bode plots.