Question
A parallel plate capacitor is made of two circular plates separated by a distance of 5 mm and with a dielectric of dielectric constant 2.2 between them. When the electric field in the dielectric is 3 × 104 V/m, the charge density of the positive plate will be close to
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6 x 10-7 C/m2
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3 x 10-7 C/m2
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3 x 104 C/m2
-
6x 104 C/m2
Solution
A.
6 x 10-7 C/m2
When free space between parallel plate capacitor, 
When dielectric is introduced between parallel plates of capacitor, 
Electric field inside dielectric 
where, K = dielectric constant of medium = -2.2
εo = permitivity of free space = 8.85 x 10-12
σ = 2.2 x 8.85 x 10-12 x 3 x 104
= 6.6 x 8.85 x 10-8 = 5.841 x10-7
= 6 x 10-7 C/m2
