8/8/2019 Op to Electronics Mcq IETE June2007

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Q.1 Choose the correct or best alternative in the following: (2x10)

a. Optical common systems use wave lengths in the range of(A) ultra violet. (B) visible.(C) x-rays. (D) infrared.

b. The optical path length in a medium equals(A) geometric path length x velocity of light in the medium.(B) geometric path length x refractive index of the medium.

(C) geometric path length / refractive index of the medium.(D) geometric path length x velocity of light in vacuum.

c. The unit for specifying material dispersion is(A) ns per nm per km. (B) ns per km.

(C) ns per . (D) none of the above.

d. The unit for PMD is(A) ns per nm per km. (B) ns per km.

(C) ns per . (D) none of the above.

e. The range for the diameter of a multimode step index or multimode GI fiber is

(A) 50-200 . (B) 5-25

(C) 500-1000 . (D) 50-200 nm.

f. The direct bandgap for a GaAeAs LED is 1.6ev. The emitted (in nm) is

(A) 775 (B) 960(C) 1300 (D) 1550

g. The diffusion length of minority carriers is given by

(A) DZ (B)

(C) (D)Where D : Diffusion constant. Z : Life time (average)

h. A laser diode has(A) spatial and temporal coherence (B) only spatial coherence(C) only temporal coherence (D) no coherence

i. The group velocity is given by

(A) (B)

(C) (D)

j. A PN photodiode, on an average, generates one electron-hole pair per five incident photons.Assuming also the photo-generated holes electrons are collected, the internal quantium efficiency

is(A) 10% (B) 20%

(C) 50% (D) 100%