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- Question
Yettrium-iron garnet (Y2Fe5O12) is a soft magnetic material suitable for applications involving
Options- A. dc
- B. 50 Hz ac
- C. ac of a few K Hz
- D. ac of a few hundred MHz
- Correct Answer
- dc
ExplanationYettrium iron garnet has very low eddy current loss. Hence it is used at frequencies in MHz range.
Materials and Components problems
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- 1. With increase in temperature, the electrical conductivity would
Options- A. increase in metals as well as in intrinsic semiconductor
- B. increase in metals but decrease in intrinsic semiconductor
- C. decrease in metals but increase in intrinsic semiconductor
- D. decrease in metals as well as in intrinsic semiconductor Discuss
Correct Answer: decrease in metals but increase in intrinsic semiconductor
Explanation:
Increase in temperature causes resistivity of metals to increase and resistivity of intrinsic semiconductors to decrease.Conductivity is reciprocal of resistivity.
- 2. Hall effect is observed in a specimen (metal or semi- conductor) when it is carrying current and is placed in a magnetic field. The resultant electric field inside the specimen is
Options- A. normal to both current and magnetic field
- B. in the same direction as current
- C. in a direction anti parallel to magnetic field
- D. none of the above Discuss
Correct Answer: normal to both current and magnetic field
- 3. The capacitance of a capacitor is not affected by
Options- A. area of plates
- B. thickness of plates
- C. ?r
- D. distance between plates Discuss
Correct Answer: thickness of plates
Explanation:
Capacitance depends on area, distance and ?r but not on thickness of plates.- 4. The charge per proton is
Options- A. 1.6 x 10-19 C
- B. 2.6 x 10-19 C
- C. 0.6 x 10-19 C
- D. 1.6 x 10-13 C Discuss
Correct Answer: 1.6 x 10-19 C
Explanation:
Because charge on proton is positive but numerically equal to that on electron.- 5. Assertion (A): If an atom of polarizability a is placed in homogeneous field E, the energy stored is 0.5 aE2.
Reason (R): Capacitance of an isolated conducting sphere R in vacuum is 4 p?0 R farads.
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
- 6. For a diamagnetic material, ?r = 1.
Options- A. True
- B. False Discuss
Correct Answer: True
- 7. An electron for which l = 0 has zero orbital magnetic dipole moment.
Options- A. True
- B. False Discuss
Correct Answer: True
- 8. A magnetic field exists around
Options- A. moving charges
- B. static charges
- C. iron
- D. copper Discuss
Correct Answer: moving charges
- 9. The resistance of a photoconductor
Options- A. increases with increase in light intensity
- B. decreases with increase in light intensity
- C. may increase or decrease with increase in light intensity
- D. remains constant Discuss
Correct Answer: decreases with increase in light intensity
- 10. The resistance of a metallic wire would
Options- A. increase as f increase
- B. decrease as f increase
- C. remains the same at all frequencies
- D. increase with f up to a certain frequency and then decrease Discuss
Correct Answer: increase as f increase
Explanation:
As increases the resistance increases due to skin effect.
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