05-01-2018, 04:52 PM
Evaporation and Sublimation
*The process of conversion of a liquid into vapour at any temperature is known as
Ans : Evaporation.
*Rate of evaporation increases with increase in temperature, surface area and decrease in pressure.
*Evaporation produces cooling of liquid. This is why we feel cool under fan while sweating.
*The process of conversion of a solid directly into vapour when heated is called
Ans : sublimation, eg: Camphor
*The quantity of heat required to convert unit mass of solid at its melting point into liquid is called
Ans : Latent Heat of Fusion .
*For ice at CPC, the latent heat of fusion is 80K cal/kg(kilo calorie / kilogram)
*The quantity of heat required to convert unit mass of a liquid at its boiling point to vapour is called
Ans : Latent Heat of Vapourisation.
*For water at 100°C, the latent heat of vapourisation is 540kcal/kg.
*Scalding with steam is more severe than that caused by boiling water because of latent heat of vapourisation.
*Heat engine is a device which converts heat energy into mechanical energy.
Black Body
*A body is said to be a perfectly blackbody if its absorption power is
*A Surface which absorbs all the heat radiations (ie radiations of all the wave length) incident on it is known as a - perfectly black body.
*A black body is a good absorber and a good emitter of heat.
*The radiation received from the sun is similar to that of a perfectly black body.
*The device used to measure the temperature of sun - Pyroheliometer
*Radiations emitted from a black body is called black body radiation.
*Heat radiation emitted from sunlight is mainly - due to infrared rays.
*The value of solar constant is -
1.34 *10^3 W/m^2
* The estimated value of surface temperature of sun is 5778K.
*Black surface is good radiator as well as a good absorber of heat. So black cloths are preferred in winter.
*White cloths are preferred in summer, as these absorb less heiat from the surroundings.
*Study of high temperature is known as Pyrology.