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
12. Germanium photodiodes have dark currents in the order of :
(a) 5 mA
(b) 10 mA
(c) 25 mA
(d) 10 A
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
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
15. LEDs fabricated from gallium arsenide emit radiation in the :
(a) Visible range
(b) Infrared region
(c) Ultraviolet region
(d) Ultrasonic region
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