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# Materials and Components – Section 5

1. 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.

 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

2.  The units for ∈r are

Explanation:

r is only a numeric. Hence no units.

3.  The real part of complex dielectric constant and tanδ for a dielectric are 2.1 and 5 x 10-4 at 100 Hz respectively. The imaginary part of dielectric constant at 100 Hz is
 A. 1.05 x 10-3 B. 2.1 x 10-3 C. 5 x 10-3 D. 1.05 x 10-2

Explanation:

4.  A copper atom is neutral. Its core has a net charge of
 A. 0 B. + 1 C. – 1 D. + 2

5.  As the temperature of semiconductor is increased
 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

Explanation:

As temperature increases, conductivity of semi- conductors increases.

6.  In anti-ferromagnetic materials, the graph of susceptibility versus temperature shows a sharp maximum at a certain temperature. This temperature is known as
 A. Curie temperature B. Neel temperature C. Weiss temperature D. Bitter temperature

7.  A parallel plate capacitor has area of plate A and plate separation d. Its capacitance is C. A metallic plate P of area A and negligible thickness is added as shown in Figure. The new value of capacitance is
 A. C B. 2C C. 0.5 C D. 0.25 C

Explanation:

The new configuration has two capacitors in series and the capacitance of each is 2C.

8.  The wavelength of light emitted by GaAs laser is 8670 x 10-10 m. If h = 6.626 x 10-34 Js, velocity of light = 3 x 108 m/s and eV = 1.602 x 10-19 J, the energy gap in GaAs is
 A. 0.18 eV B. 0.7 eV C. 1.43 eV D. 2.39 eV

9.  Diamagnetic materials do not have permanent magnetic dipoles.
 A. True B. False

10.  A piece of copper and another piece of Germanium are cooled from 30°C to 80 K. The resistance of
 A. copper decreases and germanium increases B. both decreases C. both increases D. copper increases and germanium decreases

Explanation:

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

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