Subject

Physics

Class

ICSE Class 12

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ISC Class 12 Physics Solved Question Paper 2012

Short Answer Type

41. Energy levels of H atom are given by:

E_n = $negative fraction numerator 13.6 over denominator straight n squared end fraction space eV$ where n is Principal Quantum number. Calculate the wavelength of electromagnetic radiation emitted by hydrogen atom resulting from the transition: n = 2 to n = 1.

For n = 2 ,

straight E subscript 2 space equals space fraction numerator negative 13.6 over denominator 2 squared end fraction space eV

For n= 1

straight E subscript 1 space equals space fraction numerator negative 13.6 over denominator 1 squared end fraction space eV increment straight E space equals space Emission space of space radiation space in space jumping space from space 2 space to space 1 space space straight E subscript 2 space minus space straight E subscript 1 space equals space fraction numerator negative 13.6 over denominator 4 end fraction space minus space left parenthesis negative 13.6 right parenthesis space space space space space space space space space space space space space space space space space equals space 13.6 space open square brackets 1 space minus 1 fourth close square brackets space space space space space space space space space space space space space space space space space equals space 13.6 space straight x space 3 over 4 space equals space 3.4 space straight x space 3 space eV space space space space space space space space space space space space space space space space space equals space 3.4 space straight x space 3 space straight x 10.6 space straight x space 10 to the power of negative 19 end exponent straight E space equals space straight h straight c over straight lambda straight lambda space equals space fraction numerator 6.62 space straight x space 10 to the power of negative 34 end exponent space straight x space 3 space straight x space 10 to the power of 8 over denominator 3.4 space straight x space 3 space straight x space 1.6 space straight x space 10 to the power of negative 19 end exponent end fraction space space space space equals space fraction numerator 6.62 over denominator 3.4 space straight x space 1.6 end fraction space straight x space 10 to the power of negative 34 end exponent space straight x space 10 to the power of 27 space space space equals space fraction numerator 6.62 over denominator 3.4 straight x space 1.6 end fraction space straight x space 10 to the power of negative 7 end exponent space space space space equals space 1.22 space straight x space 10 to the power of negative 7 end exponent

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42.

i) What is Compton effect ?

(ii) In Coolidge X-Ray tube (Modern X-Ray tube) how will you vary:

(1) intensity of emitted X-Rays?

(2) penetrating power of emitted X-Rays?

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43. Complete the following table for a radioactive element whose half life is 5 minutes. Assume that you have 32 g of this element at start, i.e. at t = 0.

Now, using this data, plot the “decay curve”.

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44. Calculate the energy released when an electron annihilates a positron.

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45. Draw a labelled energy band diagram for a solid which is an insulator. What is the main difference between this diagram and that of a semiconductor?

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