Ans : (a)
28. Which of the following has the least penetrating power?
     (a) Alpha particles
     (b) Beta particles
     (c) Gamma rays
     (d) All have the same penetrating power
Ans : (a)
29. Optic fibres are mainly used for which of the following? [Bank PO 1995]
     (a) Communication
     (b) Weaving
     (c) Musical instruments
     (d) Food industry
Ans : (a)
30. Which of the following are most penetrating? [BSF 1990]
     (a) α -rays
     (b) β -rays
     (c) γ -rays
     (d) X-rays
Ans : (c)
31. Old-written material, which cannot be read easily, can be read by :
     (a) cosmic rays
     (b) ultraviolet rays
     (c) infrared rays
     (d) None of these
Ans : (c)
32. Mesons are found in:
     (a) γ -rays
     (b) Laser beam
     (c) X-rays
     (d) Cosmic rays
Ans : (d)
33. The dark lines in the solar spectrum are due to: [CDS 1993]
     (a) absorption of corresponding wavelengths by the prism used in the spectrograph
     (b) destructive interference between waves of certain definite wave lengths
     (c) absorption of corresponding wavelengths by the outer layers of the sun
     (d) absence of corresponding wavelengths from the light emitted by the core of the sun
Ans : (c)
34. Which of the following is/are examples of electromagnetic waves? [NDA 1990]
     1) X-rays
     2) Ultrasonics
     3) β -rays
     4) α -rays
     (a) 1 only
     (b) 2 only
     (c) 1, 3 and 4