Ans : (c)
211. Which of the following statements are true regarding heat?
            1) Heat is a form of energy.
            2) Heat can be reflected by a mirror.
            3) Heat is an electromagnetic radiation.
            4) Heat cannot pass through vacuum.
       (a) 1, 2 and 3
       (b) 1, 2 and 4
       (c) 2, 3 and 4
       (d) 1, 3 and 4
Ans : (a)
212. Arrange in descending order of hotness the colour of the stars:
            1) Red
            2) Yellow
            3) Blue white
            4) White
       (a) 3, 4, 2, 1
       (b) 4, 3, 2, 1
       (c) 3, 2, 4, 1
       (d) 1, 2, 3, 4
Ans : (a)
213. A crystal capable of absorbing a radiation and re-emitting it in the form of visible light, does so after a -certain small time interval
     of excitation. This phenomenon is called: [CDS 2002]
       (a) phosphorescence
       (b) fluorescence
       (c) photolysis
       (d) absorption
Ans : (a)
214. Electric current passing through a metallic wire generates heat because of :[CDS 1999]
       (a) collisions of conduction electrons with each other
       (b) collisions of the atoms of the metal with each other
       (c) the energy released in the ionisation of the atoms of the metal
       (d) collisions of the conduction electrons with the atoms of the metallic wire
Ans : (c)
215. According to Einstein"s theory of relativity, when a body moves with a velocity comparable to the velocity of light, its:[CDS 1999]
       (a) mass and length decrease
       (b) mass and length increase
       (c) length increases but mass decreases
       (d) length decreases but mass increases
Ans : (c)
216. Sound travels faster in: [CDS 1999]
       (a) dry air than in water
       (b) wood than in iron
       (c) iron than in air
       (d) hydrogen than in water
Ans : (c)