Opto Electronics – Exercise – 1

1. Consider the following statements
1. LED is also known as direct gap diode
2. LCD generates light
of these statements :

(a)  1 is correct but 2 is wrong
(b)  2 is correct but 1 is wrong
(c)  both 1 & 2 are correct
(d)  both 1 & 2 are wrong

Answer
Answer : (a)
Explanation
No answer description available for this question. Let us discuss.
2. An LED is made up of :

(a)  Phosphorescent material
(b)  Germanium
(c)  Silicon
(d)  Gallium arsenide

Answer
Answer : (d)
Explanation
No answer description available for this question. Let us discuss.
3. Photoluminescence which persists for some period after excitation is known as :

(a)  Phosphorescence
(b)  Tri-luminescence
(c)  Fluorescence
(d)  Bioluminescence

Answer
Answer : (a)
Explanation
No answer description available for this question. Let us discuss.
4. In a phototransistor, the base current is :

(a)  Set by a bias voltage
(b)  Directly proportional to light
(c)  Inversely proportional to light
(d)  Square to light intensity

Answer
Answer : (b)
Explanation
No answer description available for this question. Let us discuss.
5. A photodiode is used in reverse bias because :

(a)  Majority of electron-hole pairs swept are reversed across the junction
(b)  Only one side is illuminated
(c)  Reverse current is small compared to photocurrent
(d)  Reverse current is large compared to photocurrent

Answer
Answer : (a)
Explanation
No answer description available for this question. Let us discuss.
6. A laser diode can be fabricated using :

(a)  Germanium
(b)  Silicon
(c)  Gallium arsenide
(d)  Gallium phosphide

Answer
Answer : (c)
Explanation
No answer description available for this question. Let us discuss.
7. The general condition for a phototransistor is :

(a)  Common base configuration
(b)  Common collector configuration
(c)  Common emitter configuration
(d)  Darlington-pair configuration

Answer
Answer : (c)
Explanation
No answer description available for this question. Let us discuss.
8. The power consumption of an LCD as compared to an LED is :

(a)  same
(b)  more
(c)  less
(d)  can’t be defined

Answer
Answer : (c)
Explanation
No answer description available for this question. Let us discuss.
9. When a photodiode is reverse biased, and kept in a dark room, the current flowing through the device corresponds to :

(a)  Zero current
(b)  Maximum current the device can hold
(c)  Normal current that flows through the device
(d)  Reverse saturation current

Answer
Answer : (d)
Explanation
No answer description available for this question. Let us discuss.
10. Emission of light in an LED results due to :

(a)  Emission of electrons
(b)  Photovoltaic effect
(c)  Generation of electromagnetic radiation
(d)  Conversion of heat to electrical energy

Answer
Answer : (a)
Explanation
No answer description available for this question. Let us discuss.
11. The combined package of LED and a photodiode is known as :

(a)  Optocouplers
(b)  Opto isolator
(c)  Optically coupled isolator
(d)  All of the above

Answer
Answer : (d)
Explanation
No answer description available for this question. Let us discuss.
12. Germanium photodiodes have dark currents in the order of :

(a)  5 mA
(b)  10 mA
(c)  25 mA
(d)  10 A

Answer
Answer : (b)
Explanation
No answer description available for this question. Let us discuss.
13. When a phototransistor is reverse biased, is kept in dark condition, the current flowing through the device corresponds to :

(a)  Zero current
(b)  Reverse saturation current
(c)  Maximum flow of device current
(d)  Minimum flow of device current

Answer
Answer : (b)
Explanation
No answer description available for this question. Let us discuss.
14. The colour of an LED can be changed by :

(a)  Using different band gap semiconductors
(b)  Varying the doping level of the semiconductor
(c)  Increasing applied voltage
(d)  None of the above

Answer
Answer : (b)
Explanation
No answer description available for this question. Let us discuss.
15. LEDs fabricated from gallium arsenide emit radiation in the :

(a)  Visible range
(b)  Infrared region
(c)  Ultraviolet region
(d)  Ultrasonic region

Answer
Answer : (b)
Explanation
No answer description available for this question. Let us discuss.
(a) (b) (c) (d) Answer : () [/su_spoiler]
Explanation
No answer description available for this question. Let us discuss.
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
Answer : (a)
Explanation
No answer description available for this question. Let us discuss.
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
Answer : (a)
Explanation
No answer description available for this question. Let us discuss.
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
Answer : (c)
Explanation
No answer description available for this question. Let us discuss.
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
Answer : (c)
Explanation
No answer description available for this question. Let us discuss.
(a) (b) (c) (d) Answer : () [/su_spoiler]
Explanation
No answer description available for this question. Let us discuss.
22. LED’s are fabricated from :

(a)  Si
(b)  Ge
(c)  Si or Ge
(d)  GaAs

Answer
Answer : (d)
Explanation
No answer description available for this question. Let us discuss.
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

Answer
Answer : (a)
Explanation
No answer description available for this question. Let us discuss.
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

Answer
Answer : (a)
Explanation
No answer description available for this question. Let us discuss.
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

Answer
Answer : (c)
Explanation
No answer description available for this question. Let us discuss.
26. The light emitting diode :

(a)  Usually made from metal oxide
(b)  Is Used in reverse biased condition
(c)  Gives light when temperature increases
(d)  Gives light due to electron hole recombination

Answer
Answer : (d)
Explanation
No answer description available for this question. Let us discuss.
27. The numeric aperture is the fiber optic cable’s ability :

(a)  To collect the light
(b)  To diffract the light
(c)  To reflect the light
(d)  To refract the light

Answer
Answer : (a)
Explanation
No answer description available for this question. Let us discuss.
28. An LCD requires a power of about :

(a)  20 W
(b)  20 mW
(c)  20 μW
(d)  20 nW

Answer
Answer : (d)
Explanation
No answer description available for this question. Let us discuss.
29. The advantages of opto isolators is/are :

(a)  Easy to interface with logic devices
(b)  Capable of wide band signal transmission
(c)  Problems such as noise transients, contact bounce is completely eliminated
(d)  All of the above

Answer
Answer : (d)
Explanation
No answer description available for this question. Let us discuss.
30. To display the digit 8 in a seven-segment indicator :

(a)  C must be lighted
(b)  G must be off
(c)  F must be on
(d)  All segments must be lighted

Answer
Answer : (d)
Explanation
No answer description available for this question. Let us discuss.
31. A photo-diode is normally :

(a)  forward-biased
(b)  reverse-biased
(c)  Neither forward nor reverse biased
(d)  Emitting light

Answer
Answer : (b)
Explanation
No answer description available for this question. Let us discuss.
32. When the light increases, the reverse current in a photo-diode :

(a)  increases
(b)  decreases
(c)  is unaffected
(d)  none of the above

Answer
Answer : (a)
Explanation
No answer description available for this question. Let us discuss.
33. To display the digit 0 in a seven segment display :

(a)  A must be lighted
(b)  F must be off
(c)  G must be on
(d)  all segments except G should be lighted

Answer
Answer : (d)
Explanation
No answer description available for this question. Let us discuss.
34. To display the digit 8 in a seven-segment indicator :

(a)  C must be lighted
(b)  G must be off
(c)  F must be on
(d)  All segments must be lighted

Answer
Answer : (d)
Explanation
No answer description available for this question. Let us discuss.
35. A photo-diode is normally :

(a)  forward-biased
(b)  reverse-biased
(c)  Neither forward nor reverse biased
(d)  Emitting light

Answer
Answer : (b)
Explanation
No answer description available for this question. Let us discuss.
36. When the light increases, the reverse current in a photo-diode :

(a)  increases
(b)  decreases
(c)  is unaffected
(d)  none of the above

Answer
Answer : (a)
Explanation
No answer description available for this question. Let us discuss.
37. To display the digit 0 in a seven segment display :

(a)  A must be lighted
(b)  F must be off
(c)  G must be on
(d)  all segments except G should be lighted

Answer
Answer : (d)
Explanation
No answer description available for this question. Let us discuss.