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- Question
The units for ?r are
Options- A. Farads
- B. Farads/m
- C.
- D. no units
- Correct Answer
- no units
Explanation?r is only a numeric. Hence no units.
Materials and Components problems
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- 1. Consider the following statements
- An iron cored choke is non linear and passive device.
- A carbon resistor kept in sunlight is a time invariant and passive device.
- A dry cell is a time varying and active device.
- An air capacitor is time invariant and passive device.
Options- A. 1, 2, 3 and 4 are correct
- B. 1, 2, 3 are correct
- C. 1, 2, 4 are correct
- D. 2 and 4 are correct Discuss
Correct Answer: 1, 2, 3 and 4 are correct
- 2. As per Matthiessen's rule, the total resistivity r of a conductor can be written as r = ri + aT, where ri and a are constants and T is absolute temperature. At very low temperatures
Options- A. aT = 0
- B. aT > ri
- C. aT ? ri
- D. aT < ri Discuss
Correct Answer: aT < ri
Explanation:
At very low temperatures a T ? 0. Since resistivity has a finite value even at low temperature, a T < ri.- 3. A dielectric of relative permittivity ?r is subjected to a homogeneous electric field E. The dipole moment P per unit volume is given by
Options- A. P = constant
- B. P = ?0 E
- C. P = ?0(?r - 1) E
- D. P = ?r E Discuss
Correct Answer: P = ?0(?r - 1) E
- 4. Assertion (A): The equation D = ?0?rE is applicable only to isotropic materials.
Reason (R): In polycrystalline materials, the directional effects are absent.
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 but R is not correct explanation of A
- 5. In a conductor the current flow is due to
Options- A. holes
- B. electrons
- C. ions
- D. electrons and ions Discuss
Correct Answer: electrons
- 6. A piece of copper and another piece of Germanium are cooled from 30°C to 80 K. The resistance of
Options- A. copper decreases and germanium increases
- B. both decreases
- C. both increases
- D. copper increases and germanium decreases Discuss
Correct Answer: copper decreases and germanium increases
Explanation:
As temperature is decreased, resistance of conductors decreases and resistance of semiconductors increases.- 7. Magnetic hysteresis phenomenon is explained by
Options- A. motion of domain walls
- B. motion of domain walls and domain rotation
- C. domain rotation
- D. none of the above Discuss
Correct Answer: motion of domain walls and domain rotation
- 8. The relative permeability of a ferromagnetic material is
Options- A. 1
- B. less than 1
- C. about 10
- D. 1000 or more Discuss
Correct Answer: 1000 or more
- 9. Some ceramic materials become superconducting
Options- A. below liquid helium temperature
- B. between liquid helium and liquid nitrogen temperature
- C. above liquid nitrogen but below room temperature
- D. at room temperature Discuss
Correct Answer: below liquid helium temperature
- 10. As the temperature of semiconductor is increased
Options- A. the average number of free charge carriers decreases
- B. the average number of free charge carriers increases
- C. the average number of free charge carriers remains the same
- D. the average number of free charge carriers may increase or decrease Discuss
Correct Answer: the average number of free charge carriers increases
Explanation:
As temperature increases, conductivity of semi- conductors increases.
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- 1. Consider the following statements