(d) 2, 3 and 4
Ans : (a)
35. A moderator is used in nuclear reactors in order to:
     (a) increase the number of neutrons
     (b) decrease the number of neutrons
     (c) slow down the speed of neutrons
     (d) accelerate the neutrons
Ans : (c)
36. In an atomic nucleus, neutrons and protons are held together by: [IFS 1989]
     (a) gravitational forces
     (b) magnetic forces
     (c) exchange forces
     (d) coulombic forces
Ans : (c)
37. The wave length of X-rays is of the order of: [CDS1992]
     (a) 1 cm
     (b) 1 m
     (c) 1 Angstrom
     (d) 10 micron
Ans : (c)
38. The correct sequence of various regions in absorption spectrum is :
     (a) visible, ultraviolet, microwave, infrared
     (b) Infrared, gamma rays, ultraviolet, microwave
     (c) ultra violet, visible, infrared, microwave
     (d) microwave, visible, infrared, X-rays
Ans : (c)
39. Which of the following is used as a moderator in nuclear reactor? [NDA 1993]
     (a) Ordinary water
     (b) Radium
     (c) Thorium
     (d) Graphite
Ans : (d)
40. Which of the following statements about a refrigerator is/are correct? [CDS1994]
     1) It converts electrical energy into heat energy.
     2) It converts electrical energy into mechanical energy.
     3) It transfers heat from a high temperature to a low temperature.
     4) It transfers heat from a low temperature to a high temperature.
     (a) 1and 3
     (b) 2 and 3
     (c) 1 and 4
     (d) 4 only
Ans : (c)
41. Cryogenic engines find applications in: [IAS1995]
     (a) rocket technology
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