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Anyone Good in Physics!? Help needed on a few questions.

Discussion in 'BlackHat Lounge' started by maxxwilliams, Feb 13, 2012.

  1. maxxwilliams

    maxxwilliams Junior Member

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    Hi all. Here I will post a few questions on physics and light. If anyone can help me and has time to explain how they get the answers, let me know :D

    1. Yellow light has a wavelength of 575 nm (nanometers). What is its approximate frequency?
    A. 5 x 10^12 Hz
    B. 2 x 10^14 Hz
    C. 5 x 10^14 Hz
    D. 5 x 10^15 Hz

    2. If a blackbody is heated to a temperature T (in degrees Kelvin, K, where K = ∘C + 273), the wavelength where it appears brightest (the peak of the blackbody curve) occurs at a wavelength, λpeak (in METERS), given by Wien's Law:
    λpeak x T = 0.0029
    From Wien's Law above, at what wavelength, λpeak, does a chair at room temperature (T=290 K) look brightest?

    A. 10 meters
    B. 10^-3 meters
    C. 10^-4 meters
    D. 10^-5 meters

    3. Referring to your answer from Question 2 (the Wien's Law problem), what is the corresponding frequency of that radiation?

    A. 3x10^13 Hz
    B. 4x10^13 Hz
    C. 5x10^14 Hz
    D. 5x10^15 Hz

    4. Referring once again to the Wien's law question 2, in what part of the radiation spectrum does the peak radiation occur?
    A. Visible
    B. Infrared
    C. Ultraviolet
    D. X-rays


    **Any help would be appreciate it. I think I know some of the answers, but I am trying to double check. Thanks in advance.
     
  2. BlueNebula

    BlueNebula Junior Member

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    Question 1. is C. 5 x 10^14 Hz

    :)
     
  3. nesterdwarf

    nesterdwarf Regular Member

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    1. B
    Code:
    http://answers.yahoo.com/question/index?qid=20091129202534AALzkuk
    2. D
    x(290) = .0029
    x = .0029/290
    x = 10^-5 meters

    3. A
    (3 x (10^8)) / (10^(-5)) = 3.0 × 10^13

    4. B
    Code:
    http://hyperphysics.phy-astr.gsu.edu/hbase/ems3.html#c1
    Depending on how much the big G likes me today, should be right. Could be completely wrong though...

    ND
     
  4. maxxwilliams

    maxxwilliams Junior Member

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    Hey ND, that would make #1 C. I think you have a typo there. Thanks for response Blue and ND.
     
  5. Virus1

    Virus1 Supreme Member

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    I use to be a physics tutor.... a long time ago.

    Let's see if I remember.

    speed of light = wavelength x frequency
    3 x 10^8 = wavelength x frequency

    wavelength=575 nm
    if converted to meters is 5.75 x 10^-7 Meters


    so solving for frequency:
    Frequency = speed of light /wavelength= 3x10^8 / 5.75 x 10^ -7 = 5.2 x 10 ^14 Hz

    So "C" seems to be the correct answer.


    Double check this answer... i did it from memory.... no google used.
     
  6. maxxwilliams

    maxxwilliams Junior Member

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    Yes I got C as well. Wow Virus you did that from memory and looks right on. Mind trying any of the others? I would like to see if I got them right... Or hope I did. It is always nice to have more than one mind on solving problems. :)