(c) two concave mirrors of different focal lengths
   (d) two convex lenses of unequal focal lengths
Ans: (d)
77.Which of the following is the best conductor of heat: [UPPCS (Pre) 2005]
   (a) mercury
   (b) water
   (c) leather
   (d) benzene
Ans: (a)
78.Garments keep us warm in the winter season because they: [SSC Graduate
   2004]
   (a) provide heat
   (b) do not radiate heat
   (c) prevent air from coming in the contact of the body
   (d) prevent heat of the body from going exterior
Ans: (c)
79.A glass of water does not turn into ice as it reaches 0°C. It is because- [NDA
   2012]
   (a) water does not solidify at 0°C
   (b) a certain amount of heat must be supplied to the glass of water so as to
       solidify
   (c) a certain amount of heat must be taken out from the glass of water so as
       to solidify
   (d) water solidifies at 0° K only
Ans: (c)
80.Cryogenics are used in : [IAS 1999]
   (a) space journey, surgical works and magnetic resonance
   (b) surgical works, magnetic resonance and remote sencing
   (c) space journey, surgical works and remote sencing
   (d) space journey, magnetic resonance and remote sencing
Ans: (c)
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