Question

Two 15-cm-diameter metal disks separated by a 0.66-mm-thick piece of Pyrex glass are charged to a potential difference of 1100 V What is the surface charge density on the disks? What is the surface charge density on the glass?

Answer 1

Dielectric constant of Pyrex is: k = n² = 1.47² = 2.161

The capacitance of this capacitor will be:

r = 15/2 = 7.5 cm = 0.075 m

d = 0.66 mm = 0.66 x 10^-3 m

=>

The charge on the plates will be: Q = CV = 563.5 nC

the surface charge density on the disks is then:

Since the polarization is uniform here, only the surfaces of the metal disks have charge density and so the surface charge density on glass is zero.