Opto Electronics – 1 – 5

21. GaAs LED’s emit radiation in the :

(a) Ultraviolet region
(b) Visible region
(c) Infrared region
(d) Invisible region

22. LED’s are fabricated from :

(a) Si
(b) Ge
(c) Si or Ge
(d) GaAs

23. Which material is generally used to build LED ?

(a) Compounds of gallium
(b) Compounds of phosphorus
(c) Compounds of germanium
(d) Compounds of silicon

24. A laser diode :

(a) Produces always light of single wavelength
(b) Produces always light of multiple wavelength
(c) Can be made to produce light of single and multiple wavelengths
(d) Produces visible light spectrum

25. The isolation capacitance of an opto coupler is in the order of :

(a) 0.3 – 2.5 μF
(b) 0.3 – 2.5 F
(c) 0.3 – 2.5 pF
(d) 0.3 – 2.5 nF

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