Heat And Thermodynamics
Wien's displacement Law
(i) According to this law, 
where
= wavelength corresponding to which the energy emitted per second per unit area by a perfectly black body is maximum
T = absorlute temperature of the black body
b= Wein's constant
b = 
mK .
= 
, where c denotes velocity, 
denotes frequency.
As temperature increases, colour changes towards higher frequency side.
i.e. from orange 
yellow 
green 
blue 
violet
Temperature of violet star is maximum, temperature of red star is minimum. For Sun, 
= 4753 Å (yellow colour) at temperature 6000 K. It is a medium category star.
Newton's law of cooling:
(i) According to this law, 
= K
where
= rate of loss of heat of a liquid
= difference in temperatures of liquid and the surrounding
K = constant of proportionality
(ii) As Q = 
where 
= mass, 
= specific heat of liquid
= 
= - K 
= 
Rate of fall of temperature = 
Rate of cooling = 
Rate of loss of heat = rate o cooling = 
Difference of temperature should be less than 30°C.
It is covered under forced or induced convection.
Some salient points about transmission of heat
When rates of cooling of two bodies are same, then the rate of fall of temperature of a body with highest heat capacity/thermal capacity will be the least.
If two liquids are cooled under identical conditions, rate of fall of temperature 
of that liquid will be minimum whose specific heat is maximum and vice-versa.
Less the specific heat, greater is the rate of cooling of heating.
Water has highest specific heat among liquids. It heats or cools at a low rate.
The effective area of a rough body is always greater than its geometrical area. On blackening the bottom of rough bodies, their absorptance or coefficient of absorption increases.
Solar constant:
It is defined as the amount of energy received per minute per 
of earth's surface held normally to Sun rays at mean distance of earth the from the Sun in the absence of atmosphere. S 1
or
S = solar constant = 
.
Heat radiations are electromagnetic in nature. They are transverse waves. Electrically they are neutral. They travel with velocity (c) = 
Energy of heat radiations = 
= 
= Planck's constant.
Momentum = 
, 
= frequency , 
= wavelength.
The energy distribution in the black body spectrum is not uniform. Somewhere it is maximum and somewhere minimum.
The value of radiation pressure of solar radiations = P
P = 
The formation of tail of a comet is the result or solar radiation pressure.
The radiation pressure on bigger particles is less and on smaller particles is more.
Molecular motion ceases and therefore heat exchange among various bodies ceases at absolute zero.