Subject

Physics

Class

CBSE Class 12

Pre Boards

Practice to excel and get familiar with the paper pattern and the type of questions. Check you answers with answer keys provided.

Sample Papers

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 Multiple Choice QuestionsShort Answer Type

11.

The line AB in the ray diagram represents a lens State whether the lens is convex or concave.


 

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12.

How does one explain, using de Broglie hypothesis, Bohr's second postulate of quantization of orbital angular momentum? 

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13.

What is ground wave communication? Explain why this mode cannot be used for long distance communication using high frequencies.       

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14.

The equivalent wavelength of a moving electron has the same value as that of a photon of energy 6 x 10–17 J. Calculate the momentum of the electron.

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15.

A ray of light passes through an equilateral glass prism such that the angle of incidence is equal to the angle of emergence and each of these angles is equal to 3/4 of angle of prism. Find the angle of deviation.

                                                              OR 

Calculate the speed of light in a medium whose critical angle is 45°. Does critical angle for a given pair of media depend on the wavelength of incident light? Give reason.          


Given, i = e = ¾ A,                              …(1)

where,

A is the angle of prism.

Angle of deviation for a ray of light in a prism is given by,

straight delta space equals space straight i space plus space straight e space minus space straight A

Since space straight e space equals space straight i. space we space have

straight delta space equals space 2 straight i space minus space straight A

Therefore space from space eqn. space left parenthesis 1 space right parenthesis comma space we space have space

space space space space straight delta space equals space 2 space straight x space 3 over 4 space straight A space minus space straight A
rightwards double arrow space straight delta space equals space 1 half straight A

Prism is an equilateral triangle. 

That is A= 60o

rightwards double arrow space delta space equals space 1 half cross times 60 space equals space 30 degree space semicolon space is space the space required space
angle space of space minimum space deviation. space



                                                          OR



Using the snell's law we have

mu space equals space fraction numerator 1 over denominator sin space C end fraction                                       ... (1)

where, C is the critical angle of the medium and straight mu is the refractive index of  the medium.

Also, mu space equals space c over nu                                     ... (2)

Now, from equations (1) and (2), we have 

straight c over straight nu equals straight space fraction numerator 1 over denominator sin straight space straight C end fraction

Error converting from MathML to accessible text.

This is the speed of the light in the medium. 

Refractive index of a medium is inversely proportional to the wavelength of light. So, critical angle also depends upon the wavelength of incident light.

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16.

Write two important considerations used while fabricating a Zener diode. Explain, with the help of a circuit diagram, the principle and working of a Zener diode as voltage regular. 

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17.

Draw the necessary energy band diagrams to distinguish between conductors, semiconductors and insulators.

How does the change in temperature affect the behaviour of these materials? Explain briefly. 

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18.

(a) What are the three basic units in communication systems? Write briefly the function of each of these.

(b) Write any three applications of the Internet used in communication systems. 
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19.

(a) Write the necessary conditions to obtain sustained interference fringes.

(b) In Young's double slit experiment, plot a graph showing the variation of fringe width versus the distance of the screen from the plane of the slits keeping other parameters same. What information can one obtain from the slope of the curve?

(c) What is the effect on the fringe width if the distance between the slits is reduced keeping other parameters same?

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20.

(a) Give two reasons to explain why reflecting telescopes are preferred over refracting type. 

(b) Use mirror equation to show that convex mirror always produces a virtual image independent of the location of the object.         
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