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Scientific Method and Measurements

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A person gives 200000 cal. Of heat by evapouration of water from the skin . How much water has been lost? Latent heat of evapouration of water is 2.26 10 power 6 j/kg

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Q. Indian style of cooling drinking water is to keep it in a pitcher having porous walls. Water comes to the outer surface very slowly and evaporates. Most of energy needed for evaporation is taken from the water itself and the water is cooled down. Assume that a pitcher contains 10 kg of water and 0.2 g of water comes out per second. Assuming no backward heat transfer from the atmosphere to the water, calculate the time in which the temperature decrease by 5°C. Specific heat capacity of water = 4200 J kg⁻¹ °C⁻¹ and latent heat of vaporization of water = 2.27 × 10⁶ J kg⁻¹.

Q. A closed thermally insulated vessel contains

100 g

0^{o} C

. If the an from this vessel in rapidly pumped out, intensive evaporation will produce cooling and as a result of this water will freeze. How much ice will be formed by this method? If latent heat of fusion is

80 c a l / g

and of evaporation

560 c a l / g

C_{i c e} = 0.53 c a l / g -^{\circ} C

C_{w a t e r} = 1.0 c a l / g -^{\circ} C

(L_{f})_{w a t e r} = 80 c a l / g

(L_{v})_{w a t e r} = 529 c a l / g

. A closely thermally. Insulated vessel contains

100 g

0^{\circ} C

. If the air from this vessel is rapidly pumped out, intensive evaporation will produce cooling and as a result of this water will freeze. How much ice will be formed by this method (in

g

) ? If latent heat of fusion is

80 c a l / g

and of evaporation

560 c a l / g

Q. A child running a temperature of

101^{0} F

is given an antipyrin (i.e. a medicine that lowers fever ) which causes an increases in the rate of evaporation of sweat from his body. If the fever is brought down to

98^{o} F

in 20 min, what is the average rate of extra evaporation caused, by the drug. Assume the evaporation mechanism to be the only way by which heat is lost. The mass of the child is 30 kg. The specific heat of human body is approximately the same as that of water and latent heat of evaporation of water at that temperature is about

580 c a l g^{- 1}

Q. Latent heat of ether at

0^{o}

90

cal per g. How much ether should be evaporated to freeze

60

0^{o}

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