# Materials and Components Section 1

6.  The conductivity of intrinsic semiconductor is given by
 A. eni(μp – μn) B. eni(μp + μn) C. ni(μp + μn) D. ni(μpμn)

Explanation:

For intrinsic semiconductor,

Conductivity = (Electron charge) x (Number of charge carriers) x (Sum of mobilities of holes and electrons).

7.  The core of a coil has a length of 10 cm. The self inductance is 8 mH. If the core length is doubled, all other quantities remaining the same, the self inductance will be
 A. 32 mH B. 16 mH C. 8 mH D. 4 mH

Explanation:

Inductance is inversely proportional to the core length.

8.  The minority carrier life time and diffusion constant in a semiconducting material are 100 μs and 100 cm2/s respectively. The diffusion length of carriers is
 A. 0.1 cm B. 0.01 cm C. 0.0141 cm D. 1 cm

Explanation:

Diffusion length = sqrt(Carrier life time x Diffusion constant) = (100 x 10-6 x 100)0.5 = 0.1 cm.

9.  Assertion (A): Electronic and Ionic polarization in a polyatomic gas are independent of temperature.

Reason (R): The orientation polarization is independent of temperature.

 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

Explanation:

Orientation polarization is inversely proportional to temperature.

10.  Two materials having temperature coefficients of 0.004 and 0.0004 respectively are joined in series. The overall temperature coefficient is likely to be
 A. 0.08 B. 0.04 C. 0.001 D. 0.0001

Explanation:

The overall temperature coefficient will be less than 0.004 and more than 0.0004.

11.  The number of valence electrons in pentavalent impurity is
 A. 5 B. 4 C. 3 D. 1

Explanation:

Pentavalent means 5 valence electrons.

12.  If the diameter of a wire is doubled, its current carrying capacity becomes
 A. one-fourth B. half C. twice D. four times

Explanation:

Current carrying capacity depends on area of cross-section.

13.  The law J = σE, where J is current density, σ is electrical conductivity and E is field strength is
 A. Ohm’s law B. Gauss law C. Ampere’s law D. Biot-Savart law

Explanation:

It is another form of Ohm’s law.

14.  Assertion (A): Silicon is less sensitive to changes in temperature than germanium.

Reason (R): Cut in voltage in silicon is less than that in germanium.

 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

Explanation:

Cut in voltage of silicon is higher than that in germanium.

15.  Material which lack permanent magnetic dipoles are known as
 A. paramagnetic B. diamagnetic C. ferromagnetic D. ferrimagnetic