Page 42 - Digital Book Bilingual Perpindahan Kalor
P. 42
Radiation
Why do our hands still feel hot even
when they are not directly above a
flame? Our hands continue to feel hot
because heat is transferred through
the process of radiation
Radiation is a mode of heat transfer that occurs without a medium or
intermediary. In this process, heat is transferred by electromagnetic
waves. Every object can emit electromagnetic waves, and the higher the
temperature of an object, the greater the energy of the waves it emits.
One type of these waves is infrared radiation, which carries thermal
energy. The amount of energy emitted or absorbed also depends on the
surface properties of the object; dark surfaces absorb and emit more
energy than light and shiny surfaces. This property is expressed by a
quantity called emissivity.
The equation that relates several quantities affecting the rate of heat
transfer by radiation is shown by the following equation:
Q = radiant energy (J)
T = absolute temperature (K)
ε = emissivity of the material
σ = Stefan–Boltzmann constant
A = surface area of the object (m²)
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