A piece of copper and another piece of Germanium are cooled from 30�C to 80 K. T

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Question
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

Correct Answer

copper decreases and germanium increases

Explanation

As temperature is decreased, resistance of conductors decreases and resistance of semiconductors increases.

Materials and Components problems

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2. Consider the following statements
1. An iron cored choke is non linear and passive device.
2. A carbon resistor kept in sunlight is a time invariant and passive device.
3. A dry cell is a time varying and active device.
4. An air capacitor is time invariant and passive device.
Of these statements
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

3. As per Matthiessen's rule, the total resistivity r of a conductor can be written as r = r_i + aT, where r_i and a are constants and T is absolute temperature. At very low temperatures
Options
A. aT = 0
B. aT > r_i
C. aT ? r_i
D. aT < r_i

4. 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

5. 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

8. 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

9. 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

10. For an insulating material, dielectric strength and dielectric losses should be
Options
A. high and high
B. low and high
C. high and low
D. low and low

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