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CBSE CLASS XII

Physics

21. Explain, using Huygens’ principle ,how diffraction is produced by a narrow slit which is illuminated by monochromatic light. Show that central maximum is twice as wide as the other maxima and the pattern becomes narrower as the width of the slit is increased.
22. explane
    1. State Brewster’s law.
    2. A small telescope has an objective lens of focal length 144 cm and an eyepiece of focal length 6.0 cm. What is the magnifying power of the telescope ? What is the separation between the objective and the eyepiece ?
23. What is the significance of Davisson and Germer experiment. Draw Davisson- Germer 3 electron diffraction arrangement. Where do we find the utility of the result of the experiment ?
24. Draw a diagram to show the variation of binding energy per nucleon with mass number for different nuclei. State with reason why light nuclei usually undergo nuclear fusion.
25. A 10 kg satellite circles earth once every 2 h in an orbit having a radius of 8000 km. Assuming that Bohr’s angular momentum postulate applies to satellites just as it does to an electron in the hydrogen atom , find the quantum number of the orbit of the satellite.
26. A ground receiver station is receiving a signal at
    1. 5 MHz and
    2. 100 MHz transmitted from a ground transmitter at a height of 300 m located at a distance of 100 km. Identify whether it is coming via space wave or sky wave propagation or satellite transponder.
    ( Given the value of radius of the earth is 6400 km and maximum electron density, N_max=10¹² m^-3 )
27. Explain
    1. forward biasing
    2. Reverse biasing of the p-n junction diode .With the help of a circuit diagram, explain the use of this device as a half-wave rectifier.
28. A parallel plate capacitor, each with plate area A and separation d, is charged to a potential difference V. The battery used to charge it is then disconnected. A dielectric slab of thickness d and dielectric constant k is now placed between the plates. What change, if any, will take place in :
    1. charge on plates,
    2. electric field intensity between the plates
    3. capacitance of the capacitor. Justify your answer in each case.

    OR

    1. State the principle of Van de Graaff generator and draw a labelled diagram of the generator.
    2. A parallel plate capacitor is to be designed with a voltage rating 1 kV, using a material of dielectric constant 3 and dielectric strength about 107 Vm^-1. For safety ,we would like the field never to exceed say 10% of the dielectric strength. What minimum area of the plates is required to have a capacitance of 50 pF ?
29. 1. Derive an expression for the maximum force experienced by a straight conductor of length l, carrying current I and kept in a uniform magnetic field B.
    2. A straight wire of mass 200 g and length 1.5 m carries a current of 2 A. It is suspended in mid-air by a uniform horizontal magnetic field B. What is the magnitude of the magnetic field

    OR

    1. State the principle of cyclotron and draw labelled diagram.
    2. A cyclotron’s oscillator frequency is 10 MHz .What should be the operating magnetic field for accelerating protons ? If the radius of the ‘Dees’ is 60 cm, what is the kinetic energy of the proton beam produced by the accelerator ? (e=1.60 x 10^-19 C,
       mp=1.67 x 10^-27 kg ). Express your answer in units of MeV ( 1 MeV =1.602 x 10^-13 J)
30. Draw a labelled ray diagram of an astronomical telescope, forming the image at infinity. An astronomical telescope uses two lenses powers 10 dioptre, 1 dioptre.
    1. State with reason, which lens is preferred as objective and eye-piece.
    2. Calculate the magnifying power of the telescope ,if the final image is formed at the near point.
       
    3. How do the light gathering power and resolving power of a telescope change if the aperture of the objective lens isdoubled ?

    OR

    1. An angular magnification (magnifying power) of 30 is desired using an objective of focal length 1.25 cm and an eyepiece of focal length 5 cm. How will you set up the compound microscope ?
    2. A myopic person has been using spectacles of power -1.0 dioptre for distant vision. During old age he also needs to use separate reading glass of power +2.0 dioptres. Explain what may have happened .

Submitted By : Mr. Ajay Yadav
Email: [email protected]