question_answer

Direction for: In each of the following questions a statement of Assertion is given followed by a corresponding statement of Reason just below it. Of the statements mark the correct answer as

Assertion: Light emitting diode (LED) emits spontaneous radiation. Reason: LED are forward biased p-n junctions.

A)  If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion

B)  If both Assertion and Reason are true but the Reason is not the correct explanation of the Assertion

C)  If Assertion is true but Reason is false

D)  If both Assertion and Reason are false

Correct Answer: A

Solution :

When a junction diode is forward biased as shown in figure, energy is released at the junction due to recombination of electrons and holes. In the junction diode made of gallium arsenide or indium phosphide, the energy is released in visible region. Such a junction diode is called light emitting diode or LED. The radiated energy emitted by LED is equal or less than the band gap of semiconductor.