PhysicsProf Steven E. Jones circuit shows 8x overunity ?

[poynt99]

It is a good thing you are a physics professor. I would have gotten this wrong on a test. I get:

( 500 ) * ( 40e-6 ) * ( 1.385^2 - 1.255^2 )

=  6.864 milli Joules total energy

therefore over 30 seconds =  6.864/30  =   0.2288 mW

note > watt = Joule/sec

What did I do wrong?

You should not square then subtract the capacitor voltage. You subtract the voltage, THEN square it.



.99

EDIT: Yep, you guys are correct. Ignore the above.

[xee2]

You should not square then subtract the capacitor voltage. You subtract the voltage, THEN square it.



.99

Thanks.

[nul-points]

Thanks.

xee

you, me and TinselKoala all agree that the Ein = 6.8mJ

you and i, correctly divided 6.8 by 30 seconds to give Pin = 0.23mW

you didn't do anything wrong!

[xee2]

You should not square then subtract the capacitor voltage. You subtract the voltage, THEN square it.

Hmmm... I do not agree.

starting energy = 0.5 * C * V1 * V1

end energy = 0.5 * C * V2 * V2

there fore energy change = (0.5 * C * V1 * V1) - (0.5 * C * V2 * V2) = 0.5 * C * (V1 * V1 - V2 * V2)

[poynt99]

Yep, agreed. Sorry.

.99