Materials and Components problems
- 1. The conductivity of intrinsic semiconductor is given by
Options- A. eni(?p - ?n)
- B. eni(?p + ?n)
- C. ni(?p + ?n)
- D. ni(?p?n) Discuss
Correct Answer: eni(?p + ?n)
Explanation:
For intrinsic semiconductor,
Conductivity = (Electron charge) x (Number of charge carriers) x (Sum of mobilities of holes and electrons).
- 2. Material which lack permanent magnetic dipoles are known as
Options- A. paramagnetic
- B. diamagnetic
- C. ferromagnetic
- D. ferrimagnetic Discuss
Correct Answer: diamagnetic
Explanation:
Diamagnetic materials have no permanent magnetic diploes.
- 3. If e is the charge of an electron, R is the radius of its orbit and ? is the angular velocity of electron, the magnetic dipole moment ?m of the orbit is |?m| = e?R2.
Options- A. True
- B. False Discuss
Correct Answer: False
Explanation:
1 ?m 1 = 0.5 e?r2.
- 4. Above ferroelectric curie temperature, spontaneous polarization in ferroelectric materials becomes stronger.
Options- A. True
- B. False Discuss
Correct Answer: False
Explanation:
Spontaneous polarization vanishes above ferro-electric Curie temperature.
- 5. If n denotes principal quantum number, the angular quantum number l = 0, 1... (n - 1).
Options- A. True
- B. False Discuss
Correct Answer: True
Explanation:
Angular quantum number determines the angular momentum of electron.
- 6. For a permanent magnetic material
Options- A. the residual induction and coercive field should be large
- B. the residual induction and coercive field should be small
- C. area of hysteresis loop should be small
- D. initial relative permeability should be high Discuss
Correct Answer: the residual induction and coercive field should be large
Explanation:
Materials suitable for permanent magnet have large hysteresis loop.
Hence residual and coercive field are large.
- 7. 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
Options- A. halved
- B. kept the same
- C. doubled
- D. made 4 times Discuss
Correct Answer: halved
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.
- 8. Hydrogen is used in
Options- A. large size transformers
- B. MCB
- C. large size generators
- D. circuit breakers Discuss
Correct Answer: large size generators
Explanation:
Modem large size generators have hydrogen cooling.
- 9. In a coaxial cable, braided copper is used for
Options- A. conductor
- B. shield
- C. dielectric
- D. jacket Discuss
Correct Answer: shield
Explanation:
Braided material is used for shield.
- 10. Assertion (A): At a temperature of 1000 K, thermionic emission current is about 0.1 A/cm2 of surface.
Reason (R): Thermionic emission current is given by Ith = SA0 T2 e-Ew/kT.
Options- A. Both A and R are true and R is correct explanation of A
- B. Both A and R are true but R is not correct explanation of A
- C. A is true but R is false
- D. A is false but R is true Discuss
Correct Answer: Both A and R are true and R is correct explanation of A
Explanation:
If different values are substituted in the equation for Ith the value of emission current comes out to be about 0.1 A/cm2.
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