Homework Help: physics need help

Posted by paul on Friday, January 29, 2010 at 2:26pm.

A parallel-plate capacitor made of circular plates of radius 55 cm separated by 0.25 cm is charged to a potential difference of 1000 Volts by a battery. Then a sheet of tantalum pentoxide is pushed between the plates, completely filling the gap between them. How much additional charge flows from the battery to one of the plates when the tantalum pentoxide is inserted?

where do i find the k for tantalum pentoxide?

physics need help - bobpursley, Friday, January 29, 2010 at 3:29pm
for that material, k=25
physics need help - paul, Friday, January 29, 2010 at 3:38pm
i tried that for the value of k of that material but i'm still not getting the right answer
physics need help - bobpursley, Friday, January 29, 2010 at 4:05pm
I will be happy to critique your work.
physics need help - paul, Friday, January 29, 2010 at 4:49pm
C=(kAe)/d
=[(25)(pi*.55^2)(8.85e-12)]/.0025
=8.41e-8

q1=CV
=(8.41e-8)(1000)
=8.41e-5

without dielectric:
C=(Ae)/d
=(pi*.55^2)(8.85e-12)/.0025
=3.36e-9

q2=CV
=(3.36e-9) (1000)
= 3.36e-6

q1-q2

=8.07e-5 C
physics need help - paul, Friday, January 29, 2010 at 5:46pm
this is not the right answer though. am i missing a step?
physics need help - paul, Friday, January 29, 2010 at 6:12pm
this is not the right answer though. am i missing a step?
physics need help - bobpursley, Friday, January 29, 2010 at 6:30pm
With k=25,all your math is right.
physics need help - paul, Friday, January 29, 2010 at 6:34pm
thanks, i finally got the right answer, i just needed to put more digits with the scientific notation.
thanks bob

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