Q.3 (iv) (a) What is meant by Regelation ?
(b) What is the effect of pressure on melting point of ice ?
(c) Write any one example of regelation.
Best answer
Answer: (a) Melting of ice under pressure and its refreezing when the pressure is removed; (b) pressure lowers the melting point of ice; (c) a wire with heavy weights passing through a block of ice.
(a) Regelation is the phenomenon in which ice melts when pressure is applied on it and the water formed freezes again as soon as the pressure is removed.
(b) An increase in pressure decreases the melting point of ice: ice melts below 0 ºC when pressure is applied. (For most substances pressure raises the melting point, but ice is an exception because water expands on freezing.)
(c) A thin wire with two heavy weights hung from its ends cuts slowly through a block of ice, but the ice freezes again above the wire, so the block is not divided. Skating on ice and making a snowball are other examples.
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