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Homework Help: Magnetic Fields - Extending Concepts

  1. May 26, 2009 #1
    Hi, I have 2 extremely hard questions. Any help would be appreciated so much! :)

    1. Starting from a speed of 0 m/s, a proton is accelerated through a potential difference of 32000 V. What is the proton's velocity?

    2. Is there a formula that I should use to solve for this problem?

    3. Initial Velocity = 0 m/s? What is potential difference?


    1. The energy of a proton moving through a magnetic field of intensity 0.20 T is 4.4x10^-15 J. What is the radius of the proton's path if it moves in a direction that is always perpendicular to the field?

    2. I think that I have to use Bqv = (mv^2)/r to solve for r?

    3. B = 0.20 T. I don't know what the 4.4x10^-15 J designates.
  2. jcsd
  3. May 26, 2009 #2
    Please! I need help!
  4. May 26, 2009 #3
    Please I need this soon!!!!
  5. May 26, 2009 #4


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    Since you did not post an attempt, I will give you an idea to think about. Think about energy and/or the law of conservation of energy.
  6. May 26, 2009 #5
    i'm sorry that i didn't post an attempt, but i have no idea where to start with attempting this. my teacher is dumb! she gave us the chapter test, and didn't tell us anything else. we're supposed to teach ourselves the whole chapter?!?!?! i got all of them except for these 2. it's so tedius and i don't understand what the law of conservation of energy will do to help me solve this?
  7. May 26, 2009 #6
    Here is some more hints:

    Potential difference = voltage, and the definition of voltage is...?

    for the second problem, it looks right to me, but you're missing velocity and you have energy...so which equation uses both?
  8. May 26, 2009 #7
    i still don't understand what you are trying to get me to understand about potential differnce or voltage or anything. It's nowhere in the chapter.

    And for the second one, would it be B=F/IL, becuase that's the only other equation i know. :( I hate this. Why don't I get it, can you please just tel me so I can learn instead of making me try to figure it out when I don't have anything to figure it out with or no understanding to understand your "hints?"
  9. May 26, 2009 #8


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    Do you know the charge of a proton? Given charge and potential difference can you find energy?
  10. May 26, 2009 #9


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    Actually if someone just told you, you wouldn't learn ;-) I know it may not seem that way, but being given vague hints and going through the process of figuring out the problem on your own is by far the best (some would say the only) way to really learn the material. And yes, it does involve a lot of banging your head against the wall (hopefully only figuratively though).

    From some of the questions you've been asking, I wonder whether you even know what basic concepts like voltage and energy are. If you don't, tell us! It does nobody any good for you to be getting hints that are above your level.
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