Online Electronics and Communication Engineering Test - Materials and Components Test
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- Total number of questions: 20.
- Time allotted: 30 minutes.
- Each question carries 1 mark; there are no negative marks.
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Marks : 2/20
Test Review : View answers and explanation for this test.
Diamagnetic materials have no permanent magnetic diploes.
It is another form of Ohm's law.
For intrinsic semiconductor,
Conductivity = (Electron charge) x (Number of charge carriers) x (Sum of mobilities of holes and electrons).
Assertion (A): Ferroelectric materials have spontaneous polarization.
Reason (R): Above curie temperature, ∈ = 
for ferro-electric materials.
Both A and R are correct. Spontaneous polarization vanishes above ferroelectric curie temperature.
Assertion (A): In a perfect capacitor, the current density is given by ω ∈0E0∈'rcos(ωt + 90°), where ∈r' is real part of dielectric constant.
Reason (R): In a perfect capacitor, dielectric losses are zero.
If dielectric losses are zero, the current in capacitor leads the applied voltage by 90°.
Also imaginary part of is ∈r is zero.
Assertion (A): For a solenoid having N turns, 
.
Reason (R): For all magnetic materials, B increases linearly with I.
Increase of B with I is not linear. Hence R is false.
Assertion (A): In a parallel plate capacitor having area of plate 1 m2 and plate separation 1 m, the capacitance C and resistance R are given by C = ∈0∈'r and R = 
where ω is frequency, ∈r' and ∈r" are real and imaginary parts of dielectric constant.
Reason (R): The imaginary part of electric constant is responsible for dielectric losses.
Thin film technique ensure low hysteresis and eddy current losses.
Absorption of energy is proportional to imaginary part of complex dielectric constant.
Assertion (A): Dielectric losses are proportional to tan δ.
Reason (R): tan δ = 
where ∈r' and ∈r" denote the real and imaginary parts of ∈r.
It is product of charge and distance.
Assertion (A): The equation D = ∈0∈rE is applicable only to isotropic materials.
Reason (R): In polycrystalline materials, the directional effects are absent.
Assertion (A): Holes are majority carriers in p type semiconductor.
Reason (R): In p type semiconductor, the electrons produced by thermal agitation recombine with holes.
Assertion (A): Dielectric constant is independent of temperature unless the temperature is extremely high.
Reason (R): For normal temperatures the number of atoms per unit volume is constant.
For normal temperatures the dielectric constant depends on the number of atoms per unit volume.