1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Logarithms problem

  1. Oct 25, 2014 #1


    User Avatar
    Gold Member

    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


    User Avatar
    Gold Member

    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


    User Avatar
    Gold Member

    Oh gosh. Thank you for your help :)
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Threads - Logarithms problem Date
B How to solve this specific logarithm problem Feb 14, 2017
Solving logarithmic problem Sep 10, 2014
Logarithm problem, differences! Apr 11, 2013
Problem with a logarithmic rule Jan 30, 2013
Logarithm problem Feb 15, 2011