3)    colour of evening sky.
          4)    operation of optical fibers.
          Which of the statements given above are correct? [NDA 2008]
          (a)   1 and 4
          (b)   3 and 4
          (c)   2 and 3
          (d)   1 and 2
Ans : (a)
267. Which of the following statements is/are true regarding a light wave traveling from air to glass? [NDA 2008]
                1) Its frequency remains unchanged.
                2) Its speed changes.
          (a) 1 only
          (b) 2 only
          (c) Both 1and 2
          (d) Neither 1 nor 2
Ans : (c)
268. DC current can be controlled by which one of the following components? [NDA 2008]
          (a) Impedance
          (b) Resistance
          (c) Capacitance
          (d) Inductance
Ans : (b)
269. Consider the statements; The fraction of a ball floating inside the liquid depends upon
                1) density of the liquid.
                2) mass of the ball.
                3) density of the ball.
          Which of the statements given above are correct? [NDA 2008]
          (a)   1 and 2
          (b)   2 and 3
          (c)   1 and 3
          (d)   1, 2 and 3
Ans : (c)
270. Which one among the following radiations carries maximum energy? [NDA 2008]
          (a) Ultraviolet rays
          (b) Gamma-rays
          (c) X-rays
          (d) Infrared rays
Ans : (b)
271. The neutron, proton, electron and alpha particles are moving with equal kinetic energies. How can the particles be arranged in the
     increasing order of their velocities? [NDA 2008]
          (a) Alpha particle-neutron-proton- electron
          (b) Proton-electron-neutron-alpha particle
          (c) Electron-proton-neutron-alpha particle
          (d) Neutron-proton-electron-alpha particle