Subject

Physics

Class

CBSE Class 12

Pre Boards

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Sample Papers

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 Multiple Choice QuestionsShort Answer Type

21.

How does one explain the emission of electrons from a photosensitive surface with the help of Einstein's photoelectric equation?

 

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22.

The work function of the following metals is given : Na 2.75 ev, K = 2.3 eV, Mo = 4.17 eV and Ni = 5.15 eV. Which of these metals will not cause photoelectric emission for radiation of wavelength 3300 Å from a laser source placed 1 m away from these metals? What happens if the laser source is brought nearer and placed 50 cm away?

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23.

Define the term 'amplitude modulation'. Explain any two factors which justify the need for modulating a low-frequency base band signal.

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24.

A radioactive nucleus 'A' undergoes a series of decays as given below:
straight A space rightwards arrow with straight alpha on top space straight A subscript 1 space rightwards arrow with straight beta on top space straight A subscript 2 space rightwards arrow with straight alpha on top space straight A subscript 3 space rightwards arrow with straight gamma on top space straight A subscript 4
The mass number and atomic number of A2 are 176 and 71 respectively. Determine the mass and atomic number of A4 and A.


straight A subscript 74 superscript 180 space rightwards arrow with space straight alpha space on top space straight A subscript 72 superscript 176 space rightwards arrow with space straight beta on top space straight A subscript 71 superscript 176 space rightwards arrow with straight alpha on top space straight A subscript 69 superscript 172 space rightwards arrow with straight gamma on top straight A subscript 69 superscript 172
The mass number and atomic number of A4 is 172 and 69, respectively.
The mass number and atomic number of A is 180 and 74, respectively.

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25.

Write the basic nuclear process underlying β+ and β- decays.

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26.

For a CE-transistor amplifier, the audio signal voltage across the collector resistance of 2 kΩ is 2 V. Given the current amplification factor of the transistor is 100, find the input signal voltage and base current, if the base resistance is 1 kΩ. 

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27.

Mrs Rashmi Singh broke her reading glasses. When she went to the shopkeeper to order new specs, he suggested that she should get spectacles with plastic lenses instead of glass lenses. On getting the new spectacles, she found that the new ones were thicker than the earlier ones. She asked this question to the shopkeeper but he could not offer a satisfactory explanation for this. At home, Mrs Singh raised the same question to her daughter Anuja who explained why plastic lenses were thicker.

(a) Write two qualities displayed each by Anuja and her mother.

(b) How do you explain this fact using lens maker's formula?

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28.

A narrow beam of unpolarized light of intensity I0 is incident on a Polaroid P1. The light transmitted by it is then incident on a second polaroid P2 with its pass axis making the angle of 60° relatives to the pass axis of P1. Find the intensity of the light transmitted by P2.

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29.

Explain two features to distinguish between the interference pattern in Young's double slit experiment with the diffraction pattern obtained due to a single slit.

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30.
A monochromatic light of wavelength 500 nm is incident normally on a single slit of width 0.2 mm to produce a diffraction pattern. Find the angular width of the central maximum obtained on the screen.

Estimate the number of fringes obtained in Young's double slit experiment with fringe width 0.5 mm, which can be accommodated within the region of the total angular spread of the central maximum due to the single slit.
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