249. Then term "hydroponics" is used to describe: [lFS 1990]
       (a) sound propagation under water
       (b) cultivation of plants in water
       (c) a disease in which patient develops fear of water
       (d) study of electronic devices which work underwater
Ans : (b)
250. Core of transformer is made up of: [CDS 2001]
       (a) soft iron
       (b) steel
       (c) copper
       (d) aluminium
Ans : (a)
251. Two satellites are moving in the same circular orbit around the earth. Which one of the following is correct? [NDA 2005]
     (a) The satellites must have the same mass
     (b) The satellites must have the same speed
     (c) The satellites must have the same kinetic energy
     (d) The satellites must have the same angular momentum
Ans : (d)
252. Match the following:
        Type of Electromagnetic                     Corresponding
                Radiation                             Wavelength
           A. Radiowaves                      1.   4 x 10-7 – 7 x 10-7 m
           B. Ultraviolet waves               2.   10-11 – 10-9 m
           C. Visible light                   3.   10-6 – 10-3 m
           D. X-ray                           4.   10-3 – 105 m
                                              5.   10-9 - 10-7 m
             A       B          C          D
       (a)   3       2          4          5
       (b)   4       5          1          2
       (c)   3       5          4          2
       (d)   4       2          1          5
Ans : (b)
253. Whose experiments proved that the speed of light was always the same? [CD52005]
        (a) James Clark Maxwell
        (b) Michelson and Morley
        (c) Miller and Stanley
        (d) Werner Heisenberg
Ans : (b)
254. Consider the following statements: [CDS 2009]
          X-rays
          1)   can pass through aluminium.
          2)   can be deflected by magnetic field.
          3)   move with a velocity less than the velocity of ultraviolet rays in vacuum.
          Which of the statements given above is/are correct?
                                                                    242