Opto Electronics – Exercise – 1

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

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

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

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

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

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

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