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Free download in PDF LED Short Questions and Answers for competitive exams. These short objective type questions with answers are very important for Board exams as well as competitive exams. These short solved questions or quizzes are provided by Gkseries.
41
Estimate optical power coupled into fiber of DH SLED having emission area of 1.96*10-5, radiance of 40 W/rcm2, numerical aperture of 0.2 and Fresnel reflection coefficient of 0.03 at index matched fiber surface.
[A]
5.459*10-5
[B]
1.784*10-3
[C]
3.478*102
[D]
9.551*10-5
42
In optical fiber communication, the electrical signal dropping to half its constant value due to modulated portion of optical signal corresponds to _______
[A]
6 dB
[B]
3 dB
[C]
4 dB
[D]
5 db
43
The optical 3 dB point occurs when currents ratio is equal to
44
The optical bandwidth is _____________ the electrical bandwidth.
[A]
Smaller
[B]
Greater
[C]
Same as
[D]
Zero with respect to
45
When a constant d.c. drive current is applied to device, the optical o/p power is 320 μm. Determine optical o/p power when device is modulated at frequency 30 MHz with minority carrier recombination lifetime of LED i.e. 5ns.
[A]
4.49*10-12
[B]
6.84*10-9
[C]
1.29*10-6
[D]
2.29*10-4
46
The optical power at 20 MHz is 246.2 μW. Determine dc drive current applied to device with carrier recombination lifetime for LED of 6ns.
[A]
3.48*10-4
[B]
6.42*10-9
[C]
1.48*10-3
[D]
9.48*10-12
47
Determine the 3 dB electrical bandwidth at 3 dB optical bandwidth Bopt of 56.2 MHz.
[A]
50.14
[B]
28.1
[C]
47.6
[D]
61.96
48
In surface emitter LEDs, more advantage can be obtained by using
[A]
BH structures
[B]
QC structures
[C]
DH structures
[D]
Gain-guided structure
49
As compared to planar LED structure, Dome LEDs have ______________ External power efficiency, ____________ effective emission area and _____________ radiance.
[A]
Greater, lesser, reduced
[B]
Higher, greater, reduced
[C]
Higher, lesser, increased
[D]
All the above
Answer: Higher, greater, reduced
50
The amount of radiance in planer type of LED structures is
[A]
Low
[B]
High
[C]
Zero
[D]
Cannot be determined
51
Determine CW operating lifetime for LED with βrt = -0.58 and degradation rate βr= 7.86*10-11 h-1.
[A]
32.12
[B]
42
[C]
22.72
[D]
23.223
52
Determine degradation rate βrif constant junction temperature is 17 degree celsius.
[A]
7.79*10-11
[B]
7.91*10-11
[C]
6.86*10-11
[D]
All above
53
The 3 dB electrical bandwidth B is 42 MHz. Determine 3dB optical bandwidth Bopt:
[A]
45.18
[B]
59.39
[C]
78.17
[D]
94.14
54
In optical fiber communication, ______________ major types of LED structures are used
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