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    Physics

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    ICSE Class 12

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    ISC Class 12 Physics Solved Question Paper 2011

    Multiple Choice QuestionsShort Answer Type

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    41. Starting with the law of radioactive disintegration, show that : N = N0e-λ t, where the terms have their usual meaning.

    Let N be the no. of atoms present in a radioactive substance at any instant.

    negative dN over dt space equals space lambda space N
    where, straight lambda is decay constant
    dN over straight N space equals space lambda space d t l o g subscript e space N space equals space minus space lambda to the power of plus space plus space C space w h e r e comma space C space i s space t h e space i n t e g r a t i o n space c o n s t a n t. 

    Suppose there were No atoms in the beginning them,

    N = No at t= 0

    So, log No = C

    Putting this in the above equation.

    loge N = -λ++ loge N0

    log.N = -λ+ + loge N0

    loge N - log e N0 = -λ+

    log subscript e space end subscript N over N subscript o space equals space minus lambda to the power of plus space N over N subscript o space equals space e space minus lambda to the power of plus space straight N space equals space straight N subscript straight o space straight e minus lambda to the power of plus space straight N space equals space straight N subscript straight o space straight e space minus lambda to the power of plus

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    42. What is meant by Pair Production ? Explain with the help of an example and a balanced equation.
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    43.

    An X ray tube is operated at a tube potential of 40,000 V. Calculate :

    (i) Kinetic energy of an electron emitted by the filament when it reaches the target / anode.

    (ii) Wavelengths of all the X rays emitted by the X ray tube. 

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    44. (i)In the following nuclear reaction, calculate the energy released in MeV :

    straight H presubscript 1 presuperscript 2 space plus space straight H presubscript 1 presuperscript 2 space rightwards arrow space He presubscript 2 presuperscript 3 space plus space straight n presubscript 0 presuperscript 1
    Given that: Mass of straight H presubscript 1 presuperscript 2 = 2.015 u
    Mass of He presubscript 2 presuperscript 3 space equals space 3.017 space straight u
    Mass of on = 1.009u

    (ii) What is the name of this reaction ?
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    45.

    What is meant by the terms :

    (i) a full wave rectifier ?

    (ii) an amplifier ?

    (iii) an oscillator ?  

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    46. Using several NAND gates, how can you obtain an AND gate ? Draw a labelled diagram in support of your answer.
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    Multiple Choice QuestionsLong Answer Type

    47. Obtain an expresssion for intensity of electric field in end on position. i.e., axial position of an electric dipole.  
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