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Homework Help: Microwaves energy homework

  1. Mar 13, 2010 #1
    1. The problem statement, all variables and given/known data

    GSM networks use microwaves of 20 cm in wavelength.

    The energy carried by one trillion (10^12) photons of this wavelength is closest to ...
    Question 1 answers
    A)10-16 Joules
    b)10-15 Joules
    c)10-14 Joules
    d)10-13 Joules
    e)10-12 Joules

    2. Relevant equations

    Instructions: The speed of light is c = 3 x 108 m/s

    Plank's constant is h = 6.63 x 10-34 J s

    3. The attempt at a solution

    E = hf

    c = wavelength x f
    f = (3.00 x 10^8) / (0.2) = 1.5E9
    E = 6.63 x 10-34 J s x 1.5E9
    E = 9.945E-25

    Do I Multiply by 10^12 to account for the energy carried by one trillion (10^12) photons making the answer 9.945E-13 of d from above
  2. jcsd
  3. Mar 14, 2010 #2


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    Homework Helper

    Re: Microwaves

    Well, 9.945 is quite close to 10 isn't it? So 9.945E-13 is almost 10E-13 = 10-12
    The data given in the problem are written is a strange format, they mean 10-12 (e), 10-13 (d), and so on.

  4. Mar 14, 2010 #3
    Re: Microwaves

    I thought 9.945^-13 is equivalent to 10^-13. So I do not understand why 10^-12 is the answer
    Last edited: Mar 14, 2010
  5. Mar 14, 2010 #4


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    Homework Helper

    Re: Microwaves

    You got the energy 9.945E-13. It is not the same as 9.945^-13.

    "E-13" stands for 10-13. 9.945E-13 means 9.945 multiplied by 10-13 .

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