# physics need help

posted by on .

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 - ,

for that material, k=25

• physics need help - ,

i tried that for the value of k of that material but i'm still not getting the right answer

• physics need help - ,

I will be happy to critique your work.

• physics need help - ,

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 - ,

this is not the right answer though. am i missing a step?

• physics need help - ,

With k=25,all your math is right.

• physics need help - ,

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