2)    sky is cloudy.
     3)    wind is blowing.
     Which of the statements given above is/are correct? [NDA 2004]
     (a)   1 only
     (b)   1 and 3
     (c)   2 and 3
     (d)   2 only
Ans : (a)
11. Phenomenon of formation of three dimensional image by interference of two light beams from laser or other coherent sources of
     light is called: [CDS 2003]
     (a) Optical photography
     (b) X-ray photography
     (c) Radiography
     (d) Holography
Ans : (d)
12. Consider the following statements:
     1) Atom bomb is based upon the principle of uncontrolled nuclear fusion.
     2) Hydrogen bomb is based upon the principle of uncontrolled nuclear fission.
     3) Nuclear reactor is based upon the principle of controlled nuclear fission.
     Which of the statements given above is/are correct? [NDA 2004]
     (a)   3 only
     (b)   1 and 2
     (c)   2 and 3
     (d)   1, 2 and 3
Ans : (a)
13. Which of the following waves can propagate in a vacuum? [CDS 2004]
     1) Radio waves
     2) Light waves
     3) X-rays
     4) Ultrasonic waves
     Select the correct answer using the codes given below:
     (a)   1,2 and 3
     (b)   1,2,3 and 4
     (c)   2, 3 and 4
     (d)   1 and 4
Ans : (c)
14. Paper becomes brittle and yellow with age. Why?
     1) The acid content in paper causes brittleness to develop.
     2) In the presence of visible light, photosensitised oxidation occurs.
     3) The ultra-violet component of sunlight causes photolysis of cellulose by direct cleavage of the cellulose polymer.
     (a) 1 and 2
     (b) 2and 3
     (c) 1 and 3
     (d) 1, 2 and 3
                                                                  203