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Hand crank power?

  1. Dec 2, 2003 #1
    I've seen them on radios, cell phone charges and flashlights. I haven't seen one in person, but I just want to get an idea of how they work. I'm guessing some massive gearing and a small generator/motor? And what does it use to store the energy? Or is it stored mechanical energy?
  2. jcsd
  3. Dec 2, 2003 #2
    You are correct about some gearing and a small generator. These devices can be made to utilize the hand power in different ways. I’ve seen little flashlights and radios sold to the general public that use the generator to charge a capacitor or battery. The field telephones that I’ve had for many years (circa 1952) use two D-cell batteries to send the voice signals over the wires, and the hand crank is used for ringing the bell of the phone you’re calling. What is produced is a small current and about and around 90 volts ac (when cranked swiftly). After cranking, you flip a lever on the handset to energize the system from the batteries.
  4. Dec 2, 2003 #3
    Thanks for the insight.
    By the way, to kill two birds with one stone, I will make this comment here.
    Also thanks for the info on the transformer, sorry for calling you Terry, my mistake.
    For my part box, I've been collecting everyone's old stuff for the last year, so I'm up to about 20+ transformers in my collection. It is such a shame that I threw all that stuff in the past. I use to take everything apart as a kid, but didn't know jack from didely, so I threw everything away. I would have to say it's much more fun taking the stuff apart now that I've had physics II :) Can't wait for the more serious classes.
  5. Dec 2, 2003 #4
    As a "lesson," our junior high shop teacher would have one of us hold onto a field generator's leads while another one cranked it. Needless to say, we let go of the wires ASAP! That 50 volts, I found out later, is enough to kill you. [b(]
  6. Dec 3, 2003 #5


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    Actually, getting killed by electricity is a bit wierd. It ultimately depends not only on the voltage and current, but also on the frequency.
  7. Dec 3, 2003 #6
    I guess you are referring to the body's reactance? Also, one frequency may, e. g., reinforce the heart, whereas another may cause it to defibrillate.
  8. Dec 3, 2003 #7


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    Actually, the frequency determines where the current flows. High frequency electricity is primarily conducted by the skin and is less likely to cause problems or causes different problems.

    The range of currents that cause fibrilation is relatively small, and higher currents will simply cause the entire heart to contract at once - resetting it. (Fibrilation is when the heart doesn't contract cohesively so it ceases pumping blood. Defibriliation usually refers to the application of current to try to reset or restart a heart that is fibrilating, or has stopped beating.)
  9. Dec 4, 2003 #8
    A good lesson, Nate!
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