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    Subject
    Physics

    Class

    ICSE Class 12

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    ISC Class 12 Physics Solved Question Paper 2004

    Multiple Choice QuestionsShort Answer Type

    31. Draw the circuit diagram for a common emitter NPN transistor, stating the input and output wave form. 
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    32. What are logic gates. Give the electronic circuit for the realization of AND GATE. [Diode combination showing input and output with biasing].
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    Multiple Choice QuestionsLong Answer Type

    33. State and prove Tangent law. 
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    34. A magnet makes 12 oscillations per minute in the earth’s magnetic field alone and 15 oscillations per minute when a short magnet with its axis horizontal and its south pole pointing north is placed with its center 20 cm directly above the oscillating magnet. Find the magnetic moment of the magnet. (Given : BH= 0.36 x 10-4 Tesla).
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    35. What is meant by back e.m.f. of a motor ? The back e.m.f. of a motor delivering 5 kW is 100 V, while operating on 110 V supply. Find the current and resistance of the motor. 
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    36. What are the conditions necessary for sustained interference?

    In Young’s double slit experiment the distance of the 4th Bright fringe from the central zero is 1.5 mm. The distance between the slits and the screen is 1.5 m and the distance between the slits is 2 mm. Find the wavelength of light used.
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    37. State one experiment to determine the velocity of light. Draw necessary ray diagram and derive the formula used.
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    38.

    Derive the formula for angular magnification of a compound microscope, when the final image is formed at least distance of distinct vision. Draw the required ray diagram. 

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    39.

    Give the expression for the velocity of electron in the first orbit of Hydrogen atom and for the radius in the ground state of Hydrogen atom.

    Hence derive the expression for the kinetic energy of the electron.

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    40.

    In Millikan’s oil drop experiment, a charged oil drop of density 880 kg/m3 is held stationary between two parallel plates 6.0 mm apart at a potential difference of 1000 volts. When electric field E is switched off, the oil drop was observed to fall a distance of 2.0 mm in 35.7 seconds.    [4]

    (i) Find the radius of oil drop.

    Given :

    η for air = 1.8 x 10-5 poise

    Density of air = 1.29 kg/m3

    Use g = 9.81 m/s2

    We have, 


    Speed comma space straight v space equals space fraction numerator distance space left parenthesis straight d right parenthesis over denominator time space left parenthesis straight t right parenthesis end fraction
    Here,

    Distance = 2 mm = 2 x 10 -3 m

         time = 35.7 sec


    Speed. v = fraction numerator 2 space straight x space 10 to the power of negative 3 end exponent over denominator 35.7 end fraction space equals space fraction numerator 2 over denominator 35.7 end fraction space x space 10 to the power of negative 3 end exponent

    Now, the radius of the oil drop is given by, 

    space space space space space space 6 space straight pi space straight eta space straight r space straight v space equals space 4 over 3 straight x space straight r cubed space left parenthesis straight P space minus space straight sigma right parenthesis straight g rightwards double arrow space space space 3 ηv space equals space 2 over 3 straight r squared space left parenthesis straight P space minus space straight sigma right parenthesis space straight g space rightwards double arrow space straight r squared space left parenthesis straight p minus straight sigma right parenthesis thin space straight g space equals space 9 ηv rightwards double arrow space straight r space equals space square root of fraction numerator space 9 ηv over denominator 2 thin space left parenthesis thin space straight P space minus space straight sigma right parenthesis space straight g end fraction end root  
    Here,

    η = 1.8 x 10     -5 poisse,

    P = 880 kg/m    3,

    σ = 1.29 kg/m    3 and

    g = 9.81 ms     -2

    Therefore radius of the oil drop is, 

    straight r space equals square root of space fraction numerator 9 space straight x space 1.8 space straight x space 10 to the power of negative 5 end exponent space straight x space begin display style fraction numerator 2 over denominator 35.7 end fraction end style space straight x space 10 to the power of negative 3 end exponent over denominator 2 space left parenthesis 880 space minus space 1.29 right parenthesis space 9.81 end fraction end root straight r space equals space square root of fraction numerator 9 space straight x space 1.8 space straight x space 0.056 space straight x space 10 to the power of negative 3 end exponent over denominator 2 space straight x space 878.71 space straight x space 9.81 end fraction end root space space equals space 7.254 space straight x space 10 to the power of negative 7 end exponent space straight m
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