Free items

Discussion in 'Homework' started by abdo1234, May 26, 2015.

  1. abdo1234

    abdo1234 Well-Known Member

    now that i got your attention, i will grant free items (it will be worth it) to whoever solve one or both of these 2 simple physics issues with a decent explanation of what he did

    1) in the RutherFord experiment if alpha radiation had a charge of (3.2*10^-19 C) And the core of Gold had a Charge of (126.4*10^-19) how much KE does the alpha need to obtain in order to get a (10^-14 m) distance closer to the Gold core.

    2) a ray of light with a wave length of (4144*10^-10 m) and an intensity of (3.6*10^-3 W/m^2) was directed to a surface which his space is (1*10^-4 m^2) calculate the amount of Photons that drops on the surface in 2 seconds

    note to mods : even Dota players need help before Finals.
  2. Lama051

    Lama051 Moderator

    note to abdo: there is homework section just for this kind of stuff with one of the mods solving those
  3. abdo1234

    abdo1234 Well-Known Member

    i get by this that you wont close the thread? Thanks
  4. Lama051

    Lama051 Moderator

    Moved it, changed title, left redirect in DC. Meh turns out it changes just the name of the redirect link and not the thread itself.
  5. GoSuZ

    GoSuZ Well-Known Member

    Ez free hats. If only I can remember my A-level Physics equations.
    1. -Use the idea of Conservation of Energy.
    -The EPE between two charged particles is the same as the total KE required to move the charged particle closer by a desired distance.

    2. -You get the power received by the surface by multiplying intensity with the surface area.
    -Power's alternative form of units is Joule's per second. Multiply this power by 2 to obtain the total energy obtained by the surface over the period of 2 seconds.
    -I'm pretty sure there's a relationship between Wavelength, Energy and number of Photons to help you figure out your answer. Hint: It's a formula with Planck's constant in it.

    Hopefully this will help you get the gist of how to go about the questions. I'll be around if you have anymore questions, however expect my response to be slow as I'm studying for my university statistics exams.
    Last edited: May 26, 2015
  6. Avenar

    Avenar Well-Known Member

  7. abdo1234

    abdo1234 Well-Known Member

    You hit the second question in the nuts ;D

    I still need more info about the first

    Add me for hats

    ---------- Post added at 04:52 PM ---------- Previous post was at 04:50 PM ----------

    @ avenar alpha is heleom atoms they move away from protons so you need to apply force to make them closer
  8. GoSuZ

    GoSuZ Well-Known Member

    Ah, my bad, it's the change in EPE. That would work. :3
  9. abdo1234

    abdo1234 Well-Known Member

    What about the distance where does that fit in
  10. Avenar

    Avenar Well-Known Member

    I know what Rutherford's experiment is, but the question is still unclear for me. If you check the equation I sent (UE=1/(4*Pi*Epsilon_null)*q*Q/r1), you can see that the energy and distance is inversely proportional so if you want to evaluate the energy needed to move the alpha particle 10^-14m closer you need to know where the particle is at the beginning.
  11. Drakthul

    Drakthul Well-Known Member

    Good luck for your finals!

    I suck at Physics. Don't bother.
  12. GoSuZ

    GoSuZ Well-Known Member

    That fits into your r. Take two values of r, R_[0] and R_[1] respectively.
    Suppose your initial r is R_[0] and your final r is R_[1].
    R_[1] = R_[0] - 10^-14

  13. abdo1234

    abdo1234 Well-Known Member

    Solution for #2


    ---------- Post added at 05:07 PM ---------- Previous post was at 05:05 PM ----------

    What R I'm Tottaly oblivious about the equations that I should use this is not really in my book except for "rutherford experiment"
  14. GoSuZ

    GoSuZ Well-Known Member

    ^Yeah, that's all good.
    Look up Coulomb's Law. I'm pretty sure there's a section which tells you how to calculate the Electrical Potential Energy between two charged points.

    This can probably help you. Note that this applies only to Uniform electric field which is what I guess does not 100% apply to your question.
    Last edited: May 26, 2015
  15. abdo1234

    abdo1234 Well-Known Member

    The thing is that I don't study in English so understanding this can be quite troublesome so if someone could kindly summerize it i would be really grateful
  16. GoSuZ

    GoSuZ Well-Known Member

    Hmmm... I am starting to feel that question 1 is a faulty question. Unless, you've not mentioned everything that the question is giving you.
  17. abdo1234

    abdo1234 Well-Known Member

    Eeehhh it's just "bring it closer by x distance"
  18. GoSuZ

    GoSuZ Well-Known Member

    The force exerted on a charge particle depends on its distance from the other charged particle. The closer it is, the stronger. Work done = Force * Displacement.

    Considering that the Force is not constant, you have to use the equation that both Avenar and I have shown you to calculate the work done. However, this equation requires the initial distance between your alpha particle and the gold nucleus.

    It could be possible that the answer itself is not just a number, but a function of R_[0](In the case of the image below, r_[1]), the initial distance. Then again, you claim to have not learnt this equation before which both Avenar and I believe you should have once you have learnt Coulomb's Law.

    Last edited: May 26, 2015
  19. Avenar

    Avenar Well-Known Member

    I think in the original Rutherford experiment they used Radium as an alpha radiation source. Here you can see that

    vα = velocity of alpha particle = 1.53×10^7 m/s
    mα = mass of alpha particle = 6.645×10^−27 kg

    You can calculate the KE (E0) of the original experiment (0.5mv^2).

    Then use the E0=1/(4*Pi*Epsilon_null)*q*Q/r0 to calculate r0 (original distance). Subtract the given 10^-14m (r1=r0-10^-14m) and use E1=1/(4*Pi*Epsilon_null)*q*Q/r1.
    This E1 is the KE we are looking for.

    You should check if your book mentions what kind of energy the alpha particle had in the original Rutherford experiment.
  20. abdo1234

    abdo1234 Well-Known Member

    I think the question is faulty xD