How Do You Calculate the 3dB Frequency for High and Low Pass Filters?

[Duave]

Homework Statement

(a) The input capacitor and the voltage divider network form another high pass filter. Calculate f3dB for the input high pass filter made with C = 4.7uF and the appropriate R value.

(b) calculate the f3dB for the output pass filter made with C = 4.7uF and R = 100K

https://scontent-b.xx.fbcdn.net/hphotos-ash3/t1/1660900_10151903463085919_1915092235_n.jpg

Homework Equations

f = 1/2*pi*R*C

2^N=high frequency/low frequency

The Attempt at a Solution

Question (a)
First attempt:R1 = 10k
R2 = 4.7k

R(total) = (10k)(4.7k)/(10K)+(4.7k)
R(total) = 3.20k

Hence the frequency is:

f = 1/ 2*pi*(3.20k)*(4.7uF)
f= 1/0.094499
f= 10.582HzSecond attempt:R1 = 4.7k

R(total) = 4.7k

Hence the frequency is:

f = 1/ 2*pi*(4.7k)*(4.7uF)
f= 1/0.1388
f= 7.205Hz

Question (b)

f = 1/ 2*pi*(100k)*(4.7uF)
f= 1/2.953
f= 0.3386Hz
Are any of the frequency values that were calculated correct?

Thank you

 

[berkeman]

Looks okay to me, but I don't understand what you are doing in your "second attempt" at part a).

 

[Duave]

Looks okay to me, but I don't understand what you are doing in your "second attempt" at part a).

Thank you for your response. So since the second response doesn't look right then, I will use only the first responses as my answer.

Thank you very much