plz help me
I am in class 9
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>> water kept in earthen pot during summer becomes quite cool because the earthen pot has many minute holes (very tiny holes). because of these pores, the water quickly get evaporated and the liquid will gain energy and will leave the left over water cool..
>> we are able to sip hot tea easily from a saucer rather than a cup because we know that if surface area increases, then rate of evaporation also increases. here the surface area of saucer is greater and therefore rate of evaporation will be more faster and so is the cooling rate will be greater.
>> we observe water droplets on a glass containing ice cold water because the moisture (water vapor) present in the air come in contact with glass with cold water. the surface of the glass will be cool and therefore the water vapors present in air loses it's energy and get converted into liquid state. that's why we see water droplets on he glass containing cool water.
>> during summer season, we sweat a lot and as we know cotton is a good absorber. the cotton absorbs the sweat and expose in the atmosphere.. during evaporation, the liquid particles will gain energy from our body and surroundings and will change into vapors leaving the body cool.
>> we feel so because the particles of acetone gain energy from our palm and surroundings and then evaporates.. which cause cooling effect because of latent heat of vaporisation.
>> naphthalene balls disappear without leaving any solid because of the process of sublimation. in this process, a solid is directly converted in it's gaseous state without converting in it's liquid state. this is what happens with naphthalene balls. they directly get converted in it's vapours.
>> ice at 273k cause more cooling effect than water at the same temperature because of latent heat of fusion. the particles of ice gain energy before converting into liquid. which causes more cooling effect than water.
>> this is so because the heat energy required to change in it's liquid state is used up to increase the kinetic energy and to change state. that's why the absorbed heat don't raise temperature of the particles until all solid is melted.
>> actually we don't sweat more a humid day. we feel like that because on a humid day, the moisture present in air is enough. so the sweat on our body doesn't evaporate easily and hence remains on our body. on the other hand, there is less moisture on a dry day. so the sweat on our body evaporates easily. that's why we feel like we sweat more on a humid day.
>> this means the heat energy required to change 1 kg liquid to gas at a fixed temperature at it's boiling point.
>> yes evaporation is a surface phenomenon. particles at the surface with higher kinetic energy can overcome the forced of attraction of other particles and change into it's gaseous state (vapors). if the surface area increases, then rate of evaporation also increases.
>> as I told u before in ans24. that the heat is used up in changing shape. here also, during melting, the heat energy is used up by the substance. and during this change, the molecules continues to have same kinetic energy and thus the temperature remains constant. similarly energy is used up when liquid is changing it's state to vapors. and molecules continues to have same kinetic energy and temperature remains constant.
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