Heat Transfer Perfect Blackbody
It is the exchange of thermal energy It absorbs all light/radiation in its reach.
between physical systems. According to basic laws of physics, the
The rate of heat transfer is dependent on more energy a body absorbs the more it
the temperatures of the systems and the can emit. Therefore, a black body absorbs
properties of the intervening medium all energy directed at it and also emits all
through which the heat is transferred. energy that"s been absorbed.
The three fundamental modes of heat However, if heated to a high temperature,
transfer are conduction, convection and a blackbody will begin to glow with
radiation. thermal radiation.
The energy emitted by a blackbody is
Conduction called blackbody radiation.
An energy transfer across a system Newton"s Law of Cooling
boundary due to a temperature difference
by the mechanism of intermolecular It states that the rate of change of the
interactions. temperature of an object is proportional to
It needs matter and does not require any the difference between its own
bulk motion of matter. temperature and the ambient temperature
Snow is a poor conductor and so keeps the (i.e. the temperature of its surroundings).
earth warm. T(t) = Ts + (T0 – Ts) e(-kt)
e.g. Using a heating blanket to get warm. T(t) = temperature of an object at a certain
time (Kelvin, K)
Convection t = time (s)
An energy transfer across a system Ts = temperature of the surroundings
boundary due to a temperature difference (Kelvin, K)
by the combined mechanisms of T0 = starting temperature of the object
intermolecular interactions and bulk (Kelvin, K)
transport. k = a cooling constant, specific to the
It needs fluid matter. object (1/s)
e.g. Putting your wet shoes on a floor vent Kirchhoff"s Law of Thermal Radiation
to dry them faster.
It states that wavelength-specific radiative
Radiation emission and absorption by a material
It involves the transfer of heat by body in thermodynamic equilibrium,
including radiative exchange equilibrium.
electromagnetic radiation that arises due to
the temperature of the body. It does not It signifies that good absorbers are good
need matter. emitter.
e.g. A person placing their cold hands over If a shining metal ball with some black
a warm fire. spot on its surface is heated to a high
Advection – It is the transfer of energy temperature the shining ball becomes dull
from one location to another as a side but the black spots shines brightly because
effect of physically moving an object black spot absorbs radiation during
containing that energy. heating and emit in dark.