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Logarithms problem

  1. Oct 25, 2014 #1

    Rectifier

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    Gold Member

    Hey!
    I have a question regarding a statement in my physics book. I dont see how
    [tex] |H(f)|_{dB} = - 10log (1+( \frac{f}{f_B})^2) [/tex]

    approaches this equation below for big values on f.

    [tex] |H(f)|_{dB} = - 20log ( \frac{f}{f_B}) [/tex]

    Could you please help me out?

    Thanks in advance.

    EDIT: I am sorry if this is posted to a wrong sub-forum.
     
    Last edited: Oct 25, 2014
  2. jcsd
  3. Oct 25, 2014 #2

    ShayanJ

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    When f is large, you can ignore 1 and so there only remains [itex] -10 \log{(\frac{f}{f_B})^2} [/itex]. Now you can use the property [itex] \log a^n=n\log a [/itex] to get what you want.
     
  4. Oct 25, 2014 #3

    Rectifier

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    Oh gosh. Thank you for your help :)
     
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