CBSE Physics Guess Paper17 Class XII 2009

http://www.cbseguess.com/-------------------------------------------------------------------------------------------------------www.cbseguess.com Other Educational Portals www.icseguess.com | www.ignouguess.com | www.dulife.com | www.magicsense.com Guess Paper – 2009 Class – X Subject – Physics [Semiconductor & Devices] Time – 1hr. Question no 1 to 5 – [1 Marks each]. Question no 6 to 10 – [2 Marks each]. Question no 11 to 15 – [3 Marks each]. Question no 16 & 17 – [5 Marks each]. 1. How does the energy gap of an intrinsic semiconductor vary when doped with a trivalent impurity? 2. Draw energy band diagram of n-type semiconductor. 3. A semiconductor has equal electron and hole concentration 6×108 /m3 .On doping with a certain impurity, electron concentration increases to 8×1012 /m3 .Identify the type of semiconductor after doping. 4. How does the dc current gain of a transistor change, if the width of the base region is increased? 5. Why are photodiodes used preferably in reverse bias condition? 6. In the working of a transistor, emitter base junction is forward biased, while the collector base junction is reverse biased, why: 7. Explain with the help of a circuit diagram, how the thickness of depletion layer in p-n junction diode changes when it is forward biased. 8. A transistor can not be used as a rectifier, why? 9. In a transistor base is lightly doped and is a thin layer, why? 10. What is the condition for the state of saturation of a transistor? 11. What is an intrinsic semiconductor? How can this material be converted in to (a) p type (b) n-type extrinsic semiconductor? Explain with the help of energy diagram. http://www.cbseguess.com/-------------------------------------------------------------------------------------------------------www.cbseguess.com Other Educational Portals www.icseguess.com | www.ignouguess.com | www.dulife.com | www.magicsense.com 12. Explain briefly with the help of a circuit, how V-I characteristics of a p-n junction diode are obtained in (a) Forward bias (b) Reverse bias. Draw the shape of curves obtained. 13. In a common emitter transistor amplifier, the input resistance of a transistor is 100 ohm. On changing its base current by 10µA, the collector current increases by 2mA.If a load resistance of 5kilo ohm is used in the circuit, calculate (a) current gain (b) voltage gain of the amplifier 14. In a transistor forward bias is always small as compared to Reverse bias. Explain 15. Explain the working of a Zener diode. 16. Explain the function of base region of a transistor. Draw a circuit diagram to study the input and output characteristics of NPN transistor in a common emitter (CE) configuration. Show these characteristics graphically. Explain how the current amplification factor is calculated from these Characteristics. 17. Explain the working of transistor as an oscillator. PPHHYYSSIICCSS PPOOIINNTT E-mail – physicspoint@hotmail.com Anil Kumar Pandey Email anilpandey1225@hotmail.com PP Physics Point.    FOR – XIth , XIIth & Competitive Exam.