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Electronics and Communication Engineering - Materials and Components

Exercise : Materials and Components - Section 1
16.
A parallel plate capacitor has its length, width and separation doubled. It fringing effects are neglected, to keep the capacitance same, the dielectric constant must be
halved
kept the same
doubled
made 4 times
Answer: Option
Explanation:

. When dimensions are changed, A become four times and d becomes twice.

Since ∈0 is constant, ∈r must be halved to keep C constant.

17.

Assertion (A): In imperfect capacitors, the current does not lead the applied ac voltage by 90°.

Reason (R): When subjected to ac fields, the dielectric constant can be expressed as ∈'r - j∈"r.

Both A and R are true and R is correct explanation of A
Both A and R are true but R is not correct explanation of A
A is true but R is false
A is false but R is true
Answer: Option
Explanation:

Imaginary part of ∈r gives rise to absorption of energy by the material from alternating field.

Hence current does not lead the voltage by 90°.

18.
In atomic physics, a state with l = 0 is called p state.
True
False
Answer: Option
Explanation:

The state with l = 0 is called s state.

19.
If a sample of germanium and a sample of silicon have the same impurity density and are kept at room temperature
both will have equal value of resistivity
both will have equal negative resistivity
resistivity of germanium will be higher than that of silicon
resistivity of silicon will be higher than that of germanium
Answer: Option
Explanation:

Resistivity of silicon is more than that of germanium.

20.
When an electric field E is applied to solid and liquid insulating materials, the internal field Ei acting at the location of atom is such that
Ei = E
Ei > E
Ei < E
Ei may be equal to or less than E
Answer: Option
Explanation:

The actual field seen by an atom is larger than applied field.

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