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Physics help

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slevin_kelevra
Posts: 416 - Karma: 13
I have a physics final tomorrow, and im having trouble with a couple problems.  any help would be appreciated.


An RLC series circuit has L = 100 mH and C = 1 μF. It is connected to a 1000-Hz source emf is
foundto lead the current by 75°. The value of R is:

The answer is 126 ohms, but i dont know the formula to use.

A soap film is illuminated by white light normal to its surface. The index of refraction of the film is 1.50. Wavelengths of 480 nm and 800 nm and no wavelengths between are be intensified in the reflected beam. The thickness of the film is:

The answer is 4.0 *10^(-5), same thing, I understand the concepts for the most part, but I can't seem to get the right answer.

+++karma for any help


May 9 2009 1:09AM
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slevin_kelevra
Posts: 416 - Karma: 13
i figured out the first one,I just had to use tan(theta)=X/R

but still cant figure out the second one
May 9 2009 1:23AM
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slevin_kelevra
Posts: 416 - Karma: 13
sorry for the bump... but i really need help
May 9 2009 4:14AM
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Shredneck
Posts: 2051 - Karma: -32
bump because I hated physics
May 9 2009 9:43AM
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C-Burg
Posts: 4729 - Karma: 130
for the first problem use the fact that n inductors impedance = jwL and  a capacitor = -j/wC. since they are in series just add them
May 9 2009 12:03PM
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Yeezus
Posts: 3350 - Karma: 469
is your final tomorrow, sunday, or on monday.

cuz if its on monday i could try and email my physics teacher and ask
May 9 2009 12:25PM
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C-Burg
Posts: 4729 - Karma: 130
the second one is pretty easy it's just a formula but i cant find my old formula sheet
May 9 2009 12:32PM
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slevin_kelevra
Posts: 416 - Karma: 13
yeah i got the first one, it was tan(theta)=(XL-XC)/R;

Is the second one just 2t=m(lambda)?  and plug in 800.  I know it has a phase shift of half a wavelength and im assuming it is destructive interference,but im not sure
May 9 2009 2:18PM
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slevin_kelevra
Posts: 416 - Karma: 13
No, but thanks, its in a couple of hours.

Thanks everyone for the help.  10/10 for everyone
May 9 2009 2:26PM
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donots06
Posts: 557 - Karma: 41
SO happy i'm done with physics.  circuits + electromagnetism is a bitch.
May 9 2009 8:06PM
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