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ISC Class 12 Physics Solved Question Paper 2007

Short Answer Type

31.
The distance between the first and the sixth bright fringes formed in Young’s double slit experiment (measured by a spectrometer) is found to be 12.5 mm. The separation between the slits is 0.12 mm and the distance of the screen from the slits is 60 cm. Calculate :

(i) the fringe width

(ii) the wavelength of the light used (in nm).

(i) Given,

x₆ - x₁= 12.5 mm = 12.5 x 10^-3 m

$straight x subscript 6 space equals space fraction numerator 6 λD over denominator straight d end fraction straight x subscript 1 space equals space λD over straight d Therefore comma space straight x subscript 6 space minus space straight x subscript 1 space equals space fraction numerator 6 λD over denominator straight d end fraction minus λD over straight d space equals space fraction numerator 5 λD over denominator straight d end fraction Therefore comma space fraction numerator 5 λD over denominator straight d end fraction space equals space 12.5 space straight x space 10 to the power of negative 3 end exponent space straight m rightwards double arrow space Fringe space width space equals space λD over straight d space equals space fraction numerator 12.5 space straight x space 10 to the power of negative 3 end exponent over denominator 5 end fraction space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals space 2.5 space straight x space 10 to the power of negative 3 end exponent space straight m$

ii)
Wavelength, $straight lambda space equals fraction numerator space 12.5 space straight x space 10 to the power of negative 3 end exponent space straight x space straight d over denominator 5 straight D end fraction$

Here,

d = 0.12 mm = 0.12 x 10^-3 m

D = 60 cm = 0.6 m

Therefore,

$straight lambda space equals space fraction numerator 12.5 space straight x space 10 to the power of negative 3 end exponent space straight x space 0.12 space straight x space 10 to the power of negative 3 end exponent over denominator 0.6 space straight x space 5 end fraction straight lambda space equals space 0.12 space straight x space 10 to the power of negative 6 end exponent space straight m$

$straight lambda space equals space 120 space straight x space 10 to the power of negative 9 end exponent space straight m straight lambda space equals space 120 space nm$

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32. Sketch graphically the intensity distribution in the diffraction pattern of a single slit. Label the axes.

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33.

(i) What is the difference between the electric field vector E at any point in the path of a linearly polarized light and that of an un-polarized light ?

(ii) Briefly describe how a given beam of light can be analysed and determined if it is linearly polarized or un-polarized.

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34.

A plano-convex lens made of glass (n = 1 5) has a focal length 10.0 cm.

(i) Calculate the radius of curvature of its curved surface.

(ii) If an identical plano-convex lens is placed in contact with the first (plane surfaces facing each other), what will be the power of the combination (in dioptres) ?

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35.

(i) State the three conditions for the formation of a pure spectrum.

(ii) Draw the ray diagram illustrating the measurement of the angle of a prism using a spectrometer.

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36. With the help of a ray diagram obtain the expression for the magnifying power of a simple microscope when the image is formed at the least distance of distinct vision.

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37. An astronomical telescope is adjusted to form the final image at infinity. The separation between the lenses is 80 cm. The angular magnification is 15. Calculate the focal lengths of the objective lens and the eyepiece.

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38. Draw the sketch of a simple model of a Bunsen’s grease spot photometer to compare the luminous intensity of two candles. Mention the formula used.

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39.

The work function for sodium is 2.28 eV. [3]

(i) What is the minimum energy for a quantum of radiation to cause photoelectric emission from a sodium surface ?

(ii) Calculate the wavelength of this radiation.

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40. What is meant by the mass defect ?

Calculate the disintegration energy Q when a heavy nucleus of mass number A = 240 with binding energy/nucleon ~7.6 MeV is split into two equal fragments of mass number A' = 120, each with BE/nucleon ~8.5 MeV.

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