GCSE Physics Tutorial: Dependence of Emission Intensity and Wavelength Distribution on Temperature
In the world of physics, understanding how temperature affects various properties of matter is essential. One fascinating phenomenon is how the intensity and wavelength distribution of emitted light or electromagnetic radiation are influenced by the temperature of a body. This principle is a crucial aspect of thermal radiation and is explained by a concept known as blackbody radiation.
Blackbody Radiation
A blackbody is an idealized theoretical object that absorbs all radiation incident upon it and emits radiation over a wide range of wavelengths. When a blackbody is heated, it emits electromagnetic radiation, including visible light, infrared radiation, and even a bit of ultraviolet radiation. The way in which a blackbody radiates energy depends entirely on its temperature.
Intensity of Emission
The intensity of emission refers to the amount of energy radiated by a body per unit area and per unit time. According to the Stefan-Boltzmann Law, the intensity of radiation emitted by a blackbody is directly proportional to the fourth power of its absolute temperature (measured in Kelvin). This law is expressed by the equation:
I ∝ T$^4$
Where:
I is the intensity of emission,
T is the absolute temperature.
In simpler terms, this means that as the temperature of a body increases, the intensity of the radiation it emits also increases significantly. This is why objects appear to glow brighter and emit more light as they are heated.
Wavelength Distribution
The wavelength distribution of the emitted radiation, often shown in a graph known as a blackbody radiation curve, also changes with temperature. The peak wavelength of the distribution shifts toward shorter wavelengths (higher energy) as the temperature increases. This phenomenon is described by Wien's Displacement Law:
$λ_{ \text{max}}$ ∝ $ \frac{1}{T} $
Where:
$λ_{ \text{max}}$ is the peak wavelength,
T is the absolute temperature.
In other words, as the temperature rises, the peak of the emission curve moves towards the blue end of the electromagnetic spectrum. This is why hotter objects tend to emit bluer light, while cooler objects emit redder light.
Examples in Everyday Life
Incandescent Light Bulbs: Traditional incandescent light bulbs work by heating a filament to a high temperature. As the filament gets hotter, it emits more intense light with a significant portion in the visible spectrum, but it also emits a substantial amount of infrared radiation, making it inefficient.
Stars: The colours of stars are determined by their surface temperatures. Cooler stars appear redder, while hotter stars appear bluer. This is a direct result of the relationship between temperature and the peak wavelength of emitted radiation.
Cooking: When heating metal in a fire, it starts to glow first in dull red, then progresses to orange, yellow, and eventually white as the temperature increases.
Summary
In summary, the intensity and wavelength distribution of the radiation emitted by an object depends on its temperature. The higher the temperature, the more intense the radiation and the shorter the peak wavelength of the emitted radiation. This phenomenon is a fundamental aspect of blackbody radiation and provides insights into the behaviour of various objects in our universe, from stars to everyday items that heat up.
Understanding this concept helps scientists and engineers in fields ranging from astrophysics to material science and technology, contributing to our comprehension of the natural world and enabling the development of new technologies.
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