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  QUESTIONS/SUMS BASED ON IMPORTANT CONCEPTS 1. Define Electronic device. State its two basic types. 2. Classify solids on the basis of their values of electrical conductivity and resistivity. 3. Classify semiconductors on the basis of their chemical composition. Give some examples of each. 4. Classify semiconductors on the basis of the source and the nature of the charge carriers. 5. Describe the mechanism of conduction in intrinsic semiconductors on the basis of valence bond model. 6. How do holes act as positive charge carriers? 7. Mention the limitations of intrinsic semiconductors. 8. What is doping? 9. What are the requisites of doping? 10. Mention the two types of dopants. 11.  Mention the various methods of doping. 12.  Mention the two types of extrinsic semiconductors. 13. Define 1. Valence band 2. Conduction band 3. Energy band 14. Distinguish between intrinsic and extrinsic semiconductors . 15. Distinguish between n-type and p-type semiconductors. 16. Write the...

 CLASS 12 PHYSICS   QUESTIONS/SUMS BASED ON IMPORTANT CONCEPTS (Refer text for answers) 1 Describe Thomson's Model of an atom. 2 Describe Rutherford's experiment on the scattering of alpha particles by a nucleus.  Explain the observations and conclusions of the experiment 3. Define Distance of closest approach Impact Parameter 4. Name the first atom model. 5. Name the experiment responsible for the discovery of atomic nucleus. 6. On what factors does the shape of trajectory of scattered alpha particles depend? 7. Write the formulae for 1. KE of alpha particle 2. Distance of closest approach 3. Impact Parameter  8. Mention the limitations of Rutherford's atomic model. 9. What is the distance of closest approach when a 5 MeV proton approaches a gold nucleus? 10. In a Geiger Marsden experiment, what is the distance of closest approach to the nucleus of a 7.7 MeV alpha particle before it comes momentarily to rest and reverses its direction. 11. Find the impact parameter...

    Questions/Sums on Important Concepts   Hi students,  just 9 days left for CBSE Class 12 Physics Board Exam 2025. So as a ready reckoner, I have given the answers to some of the questions here.  For derivations and graphs, please refer your textbook.                    1. Why do metals have a large number of electrons? In metals, the electrons in the outermost shells are loosely bound to the nucleus. Thus there are a large number of free electrons moving in a random manner inside the metals at room temperature. 2. Define work function of a metal. The minimum amount of energy required by an electron to just escape from the metal surface. 3. Name the different types of electron emission. Thermionic emission Field emission P hotoelectric emission Secondary emission 4. Draw the graph of effect of intensity of light on photoelectric current. Refer textbook. 5. Define Stopping potential. The value of the retarding p...