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Number of electrons leaving crystal surface. any help ?

  1. Apr 7, 2009 #1
    number of electrons leaving crystal surface. any help :)?

    1. A scanning tunnelling electron microscope (STM) measures a tiny electrical current tunnelling out of the surface of a crystal. The current is 0.30 pA (0.30 x 10-12 A).

    Calculate the number of electrons per second leaving the surface of the crystal.



    2. mass of an electron = 9.11 x 10-31 kg
    charge of an electron = -1.6 x 100-19 C



    3. I have no idea how to answer this. Thanks to anyone who has any tips or pointers :) or can show me how to work it out correctly! x
     
  2. jcsd
  3. Apr 7, 2009 #2

    LowlyPion

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    Re: number of electrons leaving crystal surface. any help :)?



    Welcome to PF.

    Neither the mass nor the charge is that useful for this. You need to look at the definition of an Ampere, which is 1 Coulomb/sec.

    A Coulomb relates to a quantity of charges. Just look it up and calculate the rest.
     
  4. Apr 7, 2009 #3
    Re: number of electrons leaving crystal surface. any help :)?

    thank you for your help :)

    I looked it up before with little success!

    so would the answer be = (0.30 x 10^-12) x (6.241 509 629 152 65 × 10^18)

    ??

    i must look incredibly stupid! just never been taught this before, finding it really hard to learn myself x
     
  5. Apr 7, 2009 #4
    Re: number of electrons leaving crystal surface. any help :)?

    oh wait.

    i think it's 0.30 x 10^-12/ 6.24150948×10^18

    before was wrong. is that the correct calculation?x
     
  6. Apr 7, 2009 #5

    LowlyPion

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    Re: number of electrons leaving crystal surface. any help :)?

    When you do the math it will be.

    You can simplify the number of digits needed however:

    (0.30 x 10-12) x (6.24 × 1018)
     
  7. Apr 7, 2009 #6
    Re: number of electrons leaving crystal surface. any help :)?

    so the answer is 1,872,000

    i'm still struggling to understand how this works. thankyou for your help
     
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