CBSE Class 12 Physics Delhi Question Paper 2013 (3)

CBSE Class 12 Physics Delhi Question Paper 2013 (3). Students can download the last year question papers using the link below. Free download of examination question papers with solutions.Last 10 year question papers should be practised to get better marks in examinations.

1. Give reasons for the following : 

(i) Long distance radio broadcasts use short-wave bands.

(ii) The small ozone layer on top of the stratosphere is crucial for human survival.

(iii) Satellites are used for long distance TV transmission.

2. (a) Draw a graph showing the variation of potential energy of a pair of nucleons as a function of their separation. Indicate the regions in which nuclear force is (i) attractive, and (ii) repulsive.

    (b) Write two characteristic features of nuclear force which distinguish it from the coluomb force. 

3. Explain, with the help of a circuit diagram, how the thickness of depletion layer in a p-n junction diode charges when it is forward biased. In the following circuit which one of the two diodes is forward biased and which is reverse biased ? 

4. (a) Show that the decay rato 'R' of a sample of a radionuclide is related tothe number of radioactive nuclei 'N' at the same instant by the expression R = lN.

    (b) The half life of 238 92 U against a-decay is 1.5 × 10¹⁷ s. What is the activity of a sample of 238

5. Draw a schematic diagram of a single optical fibre structure. Explain briefly how an optical fibre is fabricated. Describe in brief, the mechanism of propagation of light signal through an optical fibre. 

6. Distinguish between analog and digital communication. Write any two modulation techniques employed for the digital data. Describe briefly one of the techniques used. 

7. (a) Distinguish between metals, insulators and semiconductors on the basis of their energy bands.

    (b) Why are photodiodes used preferably in reverse bias condition ? A photodiode is fabricated from a semiconductor with band gap of 2.8 eV. Can it detect a wavelength of 6000 nm ? Justify. 

8.(a) Explain briefly, with the help of circuit diagram, how V—I characteristics of a p-n junction diode are obtained in (i) forward bias, and (ii) reverse bias. Draw the shape of the curves obtained.

   (b) A semiconductor has equal electron and hole concentration of 6×108/m3 . On doping with certain impurity, electron concentration increases to 9×1012/m3.

   (i) Identify the new semiconductor obtained after doping.

   (ii) Calculate the new hole concentration.

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