Opto Electronics – 1 – 4

16. The switching time of LED is in the order of :

(a) 1 second
(b) 1 microsecond
(c) 1 millisecond
(d) 1 nanosecond

ANSWER

EXPLANATION

17. The color emitted by an LED depends mainly on :

(a) Type of material used
(b) Type of biasing applied
(c) Recombination rate of charge carriers
(d)
 Environmental conditions

ANSWER

EXPLANATION

18. Compared to visible red light emitting diode, an infrared LED :

(a) Produces light with longer wavelength
(b) Produces light with shorter wavelength
(c) Produces light with medium wavelength
(d) 
Produces light of all wavelengths

ANSWER

EXPLANATION

19. In comparison to LED, LASER has :
      1. High emission frequency
      2. No tuning arrangement
      3. Narrow spectral bandwidth
      4. Provision for confinement
     Of these statements

(a) 1, 3, & 4 are correct
(b) 1, 2, & 3 are correct
(c) 1 & 3 are correct
(d) 2, 3, & 4 are correct

ANSWER

EXPLANATION

20. Match the items in Group I with items in Group II most suitably
          Group I                                                          Group II
            (P) LED                                                         (1) Heavily doped
            (Q) Avalanche photo diode                       (2) Coherent radiation
            (R) Tunnel diode                                         (3) Spontaneous emission
            (S) LASER                                                     (4) Current gain

(a) P-2, Q-1, R-3, S-4
(b) P-4, Q-3, R-2, S-1
(c) P-3, Q-4, R-1, S-2
(d) P-3, Q-2, R-1, S-4

ANSWER

EXPLANATION

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