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Opto Electronics – 1 – 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

EXPLANATION

2. An LED is made up of :

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

ANSWER

EXPLANATION

3. Photoluminescence which persists for some period after excitation is known as :

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

ANSWER

EXPLANATION

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

EXPLANATION

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

EXPLANATION

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