Stuck on Physics question - help appreciated

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need_help
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Report Thread starter 16 years ago
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Question:

Electronic photographic flash guns usually involve a capacitor being charged to a relatively high voltage, then discharged through a flash tube containing a very small quantity of xenon gas.

If a discharge is to produce a flash equivalent to a 1000W bulb lit for 1ms, calculate the voltage to which a 100 micro F (10-6) capacitor should be charged.

State any assumptions you have made.

................................ ...........................

I would appreciate any ideas. I'm currently working on a few methods but as of yet haven't reached a satisfactory answer. Cheers.

Please explain any workings you use to get your answers
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Nylex
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You can calculate the energy using E = Pt = 1000*1*10^-3

You can then use E = (1/2)CV^2 to calculate the voltage across the capacitor. Rearrange in terms of V and then substitute your value for E in.
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need_help
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(Original post by Nylex)
You can calculate the energy using E = Pt = 1000*1*10^-3

You can then use E = (1/2)CV^2 to calculate the voltage across the capacitor. Rearrange in terms of V and then substitute your value for E in.
ahh....cunning - cheers
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Nylex
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(Original post by need_help)
ahh....cunning - cheers
No prob. Assumptions: I think you say you're assuming that exactly half of the energy stored in the capacitor is used to produce the flash, the other half will be wasted. Not 100% sure on that though.
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Rustyk1
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(Original post by Nylex)
No prob. Assumptions: I think you say you're assuming that exactly half of the energy stored in the capacitor is used to produce the flash, the other half will be wasted. Not 100% sure on that though.
no, i think this last bit is wrong. you are assuming that 100% of the energy stored in the capacitor is used to produce the flash. in reality this ofcourse is wrong as energy is lost as heat, sound (a bit) etc.
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