Subject

Physics

Class

CBSE Class 12

Pre Boards

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Sample Papers

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 Multiple Choice QuestionsShort Answer Type

21.

Which mode of propagation is used by short wave broadcast services?


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22.

Why are infra-red waves often called heat waves? Explain.


Infrared waves produced from hot bodies. Hence, it often called heat waves.


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23.

What do you understand by the statement - Electromagnetic waves transport momentum?


24.

If light of wavelength 412.5 nm is incident on each of the metals given below, which ones will show photoelectric emission and why?

Metal Work Function (eV)
Na 1.92
K 2.15
Ca 3.20
Mo 4.17


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25.

A carrier wave of peak voltage 15 V is used to transmit a message signal. Find the peak voltage of the modulating signal in order to have a modulation index of 60%.


26.

Show using a proper diagram how unpolarised light can be linearly polarised by reflection from a transparent glass surface.


27.

The figure shows a ray of light falling normally on the face AB of an equilateral glass prism having refractive index 3/2, placed in water of refractive index 4/3. Will this ray suffer total internal reflection on striking the face AC? Justify your answer.


28.

If one of two identical slits producing interference in Young’s experiment is convered with glass, so that the light intensity passing through it is reduced to 50%, find the ratio of the maximum and minimum intensity of the fringe in the interference pattern.


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29.

What kind of fringes do you expect to observe if white light is used instead of monochromatic light?


30.

A symmetric biconvex lens of the radius of curvature R and made of glass of refractive index 1.5, is placed on a layer of liquid placed on top of a plane mirror as shown in the figure. An optical needle with its tip on the principal axis of the lens is moved along the axis until its real, inverted image coincides with the needle itself. The distance of the needle from the lens is measured to be x. On removing the liquid layer and repeating the experiment, the distance is found to bey. Obtain the expression for the refractive index of the liquid in terms of x and y.


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