Download engineering physics ii dielectrics

ENGINEERING PHYSICS II
DIELECTRICS
PROBLEMS
1. Calculate the dielectric constant of a material which when inserted in parallel condensor of area
10mm x 10mm and distance of separation of 2 mm, gives a capacitance of 10-9 F.
Solution:
∈𝑜 ∈𝑟 𝐴
𝐶=
𝑑
𝐶𝑑
∈𝑟 =
∈𝑜 𝐴
=
10−9 × 2 × 10−3
8.854 × 10−12 × 10−6
∈𝐫 = 𝟐𝟐𝟓𝟗
∴ The relative permittivity of the material is ∈𝒓 =2259 (no unit)
2. A crystal subjected to an electric field of 1000 Vm-1 and the resultant polarisation is 4.3 ×10-8
C/m2. Calculate the relative permittivity of the crystal.
Solution
𝑃
=∈𝑜 (∈𝑟 − 1)
𝐸
𝑃
∈𝑟 − 1 =
∈𝑜 𝐸
∈𝑟 =
𝑃
∈𝑜 𝐸
+ 1
4.3 × 10−8
∈𝑟 =
+ 1
8.85 × 10−12 × 1000
∈𝑟 = 4.8588 + 1
∈𝑟 = 5.8588
∴ The relative permittivity of the crystal is ∈𝒓 =5.8588 (no unit)
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