(a) warm and moist
   (b) cool and dry
   (c) warm and dry
   (d) cool and moist
Ans: (d)
305. The velocity of sound in air increases with
   (a) the rise of temperature
   (b) rise of its frequency
   (c) decrease in humidity
   (d) fall of temperature
Ans: (a)
306. The velocity of sound in a medium is
   (a) directly proportional to its pressure
   (b) inversely proportional to the square root of its pressure
   (c) directly proportional to the square root of its pressure
   (d) independent of its pressure
Ans: (d)
307. Which of the following is not electromagnetic waves?
   (a) heat waves
   (b) sound waves
   (c) radio waves
   (d) light waves
Ans: (b)
308. When light passes from air to glass, its velocity in glass
   (a) increases
   (b) decreases
   (c) remains unchanged
   (d) first decreases then increases
Ans: (b)
309. To produce beats it is necessary to have two waves
   (a) travelling in opposite direction
   (b) of slightly different frequencies
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