Chapter: Physics : Dielectric Materials
Solved Problems: Dielectric Materials
SOLVED PROBLEMS
1.Find the capacitance of a layer of Al2O3that
is 0.5 m thick and 2000 mm2 of square area ( r = 8.854 ×
10–12 Fm–1)
Solution:
Given data:
2.A layer of porcelain is 80 mm long, 20 mm
wide and 0.7 µm thick. Calculate its capacitance with r = 6
Solution:
Given data:
3.If an ionic crystal is subjected to an
electric field of 1000 Vm–1 and the resulting polarization 4.3 × 10–8
cm2. Calculate the relative permittivity of NaCl. Solution:
Given data:
4.Calculate the electronic Polarization of
argon atom. Given at r =
1.0024 at NTP and N = 2.7 × 1025 atom m–3 .
Solution
:
Relative permitivity = 1.0024 at NTP
Permitivity of free space = 8.854 × 10–12
Fm–1
5.A
solid contains 5 × 1028 atoms/m3 each with a
polarisability of 2×10–40 F m2. Assuming that the
internal field is given by Lorentz formula. Calculate the ratio of internal
field to the external field. 0 = 8.854 × 10–12 Fm–1.
6.
Calculate the polarization produced in dielectric medium of dielectric
constant 6 when it is subjected to an electric field of 100 Vm–1. (e0 = 8.854 × 10–12 Fm–1)
P = 4.425 × 10–9 Vm–2 F
7. Calculate the electronic polarizability of
neon. The radius of neon atom is 0.158 nm. (
= 8.854 × 10–12 Fm–1)
8.The dielectric constant of a helium gas at
NTP is 1.0000684. Calculate the electron polarizability of helium atoms if the
gas contains 2.7 × 1026 atoms/m3 and hence calculate the
radius of helium atom ( = 8.854 × 10–12 Fm–1)
Solution:
1. The electronic
polarisability is 0.18x 10 40 fm2. Find the relative
dielectric constant at 0C and 1 atmospheric pressure. (Ans: 1.000055)
A
capacitor has capacitance of 0.019 F when uses wax paper r 1.85
between the electrodes of Aluminum foil. The wax paper is to be replaced by
plastic film r 2.15 of same dimensions. Taking other factors being
equal, obtain the change (increase/decrease) in capacitance.
(Ans:
Increase of 0.0117 F)
A
capacitor uses Aluminum oxide as the dielectric with relative permeability = 8.
An effective surface area of 360 cm2 gives a capacitance of 6 F .
Calculate the field strength and the total dipole moment induced in oxide layer
if a potential difference of 15 volts exist across the capacitor.
(Ans:
(i) 3.535 × 107 V/m (ii) 33.4 x 10 C – m)
The
radium of the Helium atom is about 0..55 AU. Calculate the polarisability of
Helium and its relative permeability. The number of Helium atoms in a volume of
1 m is 2.7 × 1025 atoms. (Ans:
(i) 0.185 × 10–40 Farad –
m² (ii) 1.000057)
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