Posted by paul on .
A parallelplate 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,
for that material, k=25

physics need help 
paul,
i tried that for the value of k of that material but i'm still not getting the right answer

physics need help 
bobpursley,
I will be happy to critique your work.

physics need help 
paul,
C=(kAe)/d
=[(25)(pi*.55^2)(8.85e12)]/.0025
=8.41e8
q1=CV
=(8.41e8)(1000)
=8.41e5
without dielectric:
C=(Ae)/d
=(pi*.55^2)(8.85e12)/.0025
=3.36e9
q2=CV
=(3.36e9) (1000)
= 3.36e6
q1q2
=8.07e5 C 
physics need help 
paul,
this is not the right answer though. am i missing a step?

physics need help 
bobpursley,
With k=25,all your math is right.

physics need help 
paul,
thanks, i finally got the right answer, i just needed to put more digits with the scientific notation.
thanks bob