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Homework Help: Energy Fluxes of Two Objects

  1. Feb 8, 2012 #1
    1. The problem statement, all variables and given/known data
    Suppose two objects have energy fluxes, f and f + Δf, where
    Δf ≪ f. Derive an approximate expression for the magnitude difference
    Δm between these objects. Your expression should have Δm
    proportional to Δf.

    2. Relevant equations
    Δm = m2 - m1 = 2.5 * log(f1/f2)

    3. The attempt at a solution
    So the issue is that I'm not sure which of these solutions would be the better one to work with. However, I did make an approximation with the one as shown below and I'm not sure if it is quite accurate enough. Any assistance is greatly appreciated.

    Attempt 1: Δm = 2.5 * log(f / f+Δf) = 2.5 * [ log(f) - log (f + Δf)]


    Attempt 2: Δm = 2.5 * log(f+Δf / f) = 2.5 * log(1 + Δf/f) ≈ 2.5*Δf

    The second attempt seems more correct to me but I would feel more confident with a second opinion.
  2. jcsd
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