basically a p-n junction operating in a photovoltaic mode without external bias. Working: When light photons fall at the junction electron-hole pairs are generated. those more in opposite direction due to junction field. These charges accumulate at the two sides of the junction and photo voltage is developed. Use: It is used in calculators etc.SOME IMPORTANT QUESTIONS FROM PREVIOUS YEAR PAPERS (CHAPTER-ELECTRONIC DEVICES) 1.In a semiconductor the concentration of electorns is 8x1013cm-3 and that of holes is 5x1012cm-3. Is a p-type or n-type semiconductor? Ans : As concentration of electrons is more than holes, the given extrinsic semi conductor is n-type. 2.The energy gaps in the energy band diagrams of a conductor, semiconductor and insulator are E1, E2 and E3. Arrange them in increasing order. Ans: the energy gap in a conductor is zero, in a semiconductor is ≈ 1eV and in an insulator is ≥ 3eV. E1=0, E2=1eV, E3≥3eV . E1 < E2 < E3. 3. Find the truth table of following gates….4. Find the truth table of following gates….5.Name the fundamental gates. Ans : OR, AND and NOT gates. 6.What is the width of dipletion layer in p-n junction diode? Ans : The depletion layer in junction diode is of the order of micrometer (≈10-6m) 7.The current gain (α) of a transister in common base configuration is 0.98. What does It physically mean? Ans :The current gain α=0.98 means that 98% of charge carriers of an emitter reach the collector and constitute the collector current 8.In the following diagrams, write which of the diodes are forward biased and which are reverse biased Ans : The junction diode in figs (b) and (d) are forward biased and (a) and (c) are reverse biased. 9.Name the gate obtained from the combination of gates shown if figure. Draw the
basically a p-n junction operating in a photovoltaic mode without external bias. Working: When light photons fall at the junction electron-hole pairs are generated. those more in opposite direction due to junction field. These charges accumulate at the two sides of the junction and photo voltage is developed. Use: It is used in calculators etc.SOME IMPORTANT QUESTIONS FROM PREVIOUS YEAR PAPERS (CHAPTER-ELECTRONIC DEVICES) 1.In a semiconductor the concentration of electorns is 8x1013cm-3 and that of holes is 5x1012cm-3. Is a p-type or n-type semiconductor? Ans : As concentration of electrons is more than holes, the given extrinsic semi conductor is n-type. 2.The energy gaps in the energy band diagrams of a conductor, semiconductor and insulator are E1, E2 and E3. Arrange them in increasing order. Ans: the energy gap in a conductor is zero, in a semiconductor is ≈ 1eV and in an insulator is ≥ 3eV. E1=0, E2=1eV, E3≥3eV . E1 < E2 < E3. 3. Find the truth table of following gates….4. Find the truth table of following gates….5.Name the fundamental gates. Ans : OR, AND and NOT gates. 6.What is the width of dipletion layer in p-n junction diode? Ans : The depletion layer in junction diode is of the order of micrometer (≈10-6m) 7.The current gain (α) of a transister in common base configuration is 0.98. What does It physically mean? Ans :The current gain α=0.98 means that 98% of charge carriers of an emitter reach the collector and constitute the collector current 8.In the following diagrams, write which of the diodes are forward biased and which are reverse biased Ans : The junction diode in figs (b) and (d) are forward biased and (a) and (c) are reverse biased. 9.Name the gate obtained from the combination of gates shown if figure. Draw the
physics-xii-15-16.docx