As per Matthiessen's rule, the total resistivity r of a conductor can be written

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Question
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

Correct Answer

aT < r_i

Explanation

At very low temperatures a T ? 0. Since resistivity has a finite value even at low temperature, a T < r_i.

Materials and Components problems

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1. 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

2. 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

4. Assertion (A): Intrinsic resistivity of silicon is lower than that of germanium.
Reason (R): Magnitude of free electron concentration in germanium is more than that of silicon.
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

6. 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

8. 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

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