(b) r/3
   (c) 3r
   (d) r3
Ans: (b)
184. In summer season a fan gives us relaxation because: [NDA 2010]
   (a) our body radiates more heat comparatively in air
   (b) fan provides cold air
   (c) the conductivity of air is increased
   (d) our sweat vapourises very quickly
Ans: (d)
185. The ratio of the velocities of X-rays and y-rays is : [NDA 2010]
   (a) <1
   (b) >1
   (c) 1
   (d) depends on the ratio of their frequencies
Ans: (c)
186. The nuclear force exists between:
   (a) proton - proton
   (b) proton - neutron
   (c) neutron - neutron
   (d) All of these
Ans: (d)
187. In the following rays pair which one is found to be naturally
   electromagnetic? [NDA 2010]
   (a) β-rays and γ -rays
   (b) Cathode rays and X-rays
   (c) α-rays and β-rays
   (d) X-rays and γ-rays
Ans: (d)
188. The nuclear force is :
   (a) attractive and spin dependent
   (b) attractive but spin independent