In physics, the concepts of absorbed energy and emitted energy play a crucial role in understanding atomic behavior, quantum mechanics, and electromagnetic radiation. The value of absorbed and emitted energy follows quantized principles, meaning that energy changes occur in discrete amounts rather than continuous values.
This principle was first introduced in Bohr’s atomic model and later refined through quantum mechanics. In this topic, we will explore how energy absorption and emission occur, the formulas governing these transitions, and their applications in real-world physics.
Understanding Absorbed and Emitted Energy
What is Absorbed Energy?
Absorbed energy refers to the energy an atom, molecule, or ptopic gains from an external source. This energy can come from electromagnetic radiation, heat, or ptopic collisions. When an electron in an atom absorbs energy, it moves to a higher energy level (excited state).
What is Emitted Energy?
Emitted energy occurs when an atom or molecule loses energy and releases it in the form of light (photons), heat, or other forms of radiation. When an excited electron returns to a lower energy state (ground state), it releases the excess energy as a photon.
This emission of energy is responsible for many natural phenomena, including the colors of neon lights, the spectrum of stars, and the fluorescence of certain materials.
Quantization of Energy Levels
One of the key principles governing absorbed and emitted energy is quantization. This means that an electron can only absorb or emit specific amounts of energy, corresponding to differences between discrete energy levels.
Bohr’s Energy Equation
Niels Bohr formulated a mathematical expression to determine the energy levels of electrons in a hydrogen atom:
Where:
â E_n = Energy of the electron in the nth orbit
â n = Principal quantum number (1, 2, 3, …)
â -13.6 eV = Energy of the electron in the ground state of hydrogen
This equation tells us that the energy of an electron becomes less negative (higher energy) as it moves to higher quantum levels.
Energy Difference and Photon Emission
The energy of absorbed or emitted radiation follows the equation:
Where:
â ÎE = Energy difference between two states
â h = Planck’s constant (6.626 à 10â»Â³â´ J·s)
â f = Frequency of the emitted or absorbed photon
This equation states that the energy change corresponds to the frequency of light emitted or absorbed. The larger the energy difference, the higher the frequency of the emitted or absorbed photon.
Absorption and Emission Spectra
Absorption Spectrum
An absorption spectrum is produced when atoms absorb specific wavelengths of light, causing electrons to move to higher energy levels. These absorbed wavelengths appear as dark lines in a continuous spectrum.
This process is used in spectroscopy to identify elements in distant stars and gases.
Emission Spectrum
An emission spectrum occurs when electrons release energy and return to lower energy levels. The emitted light produces bright spectral lines corresponding to specific energy transitions.
Different elements have unique emission spectra, which help scientists analyze the composition of stars, gases, and chemical substances.
Examples of Absorbed and Emitted Energy
1. Neon Lights
Neon lights operate based on the principle of electron excitation and emission. When an electric current passes through a gas (e.g., neon), electrons absorb energy and move to a higher level. When they return to the ground state, they emit visible light of specific colors.
2. Fluorescence
Fluorescent materials absorb high-energy ultraviolet light and re-emit it as visible light. This process is used in fluorescent lamps, glow-in-the-dark materials, and biological markers in medical imaging.
3. The Sun and Stars
Stars, including the Sun, produce energy through nuclear fusion, where hydrogen atoms fuse to form helium, releasing enormous amounts of energy. The emitted energy follows specific spectral patterns, allowing scientists to determine a star’s composition, temperature, and age.
4. Blackbody Radiation
All objects emit radiation depending on their temperature. A hotter object emits more energy at shorter wavelengths (blue light), while a cooler object emits energy at longer wavelengths (red light). This principle explains why heated metals glow red-hot and why the Sun appears yellow-white.
The Relationship Between Energy, Wavelength, and Frequency
The energy of emitted or absorbed radiation is related to wavelength and frequency using the equation:
Where:
â E = Energy of the photon
â h = Planck’s constant
â c = Speed of light (3.0 à 10⸠m/s)
â λ = Wavelength of the photon
This equation shows that shorter wavelengths (higher frequency) correspond to higher energy, while longer wavelengths (lower frequency) correspond to lower energy.
Practical Applications of Energy Absorption and Emission
1. Lasers
Lasers work by exciting atoms to high-energy states and then stimulating them to emit coherent, focused light. This principle is used in medical surgery, barcode scanners, and fiber-optic communication.
2. Night Vision Goggles
Night vision technology detects infrared radiation emitted by warm objects. Special sensors absorb infrared energy and convert it into a visible image.
3. Solar Panels
Solar cells absorb sunlight and convert it into electrical energy using the photoelectric effect, where light energy excites electrons to produce an electric current.
4. X-ray Imaging
X-rays are high-energy photons emitted when electrons transition in heavy atoms. They are used for medical imaging, security scanning, and industrial inspection.
The value of absorbed and emitted energy is governed by the principles of quantum mechanics, where electrons transition between discrete energy levels. The amount of energy absorbed or emitted is quantized and follows specific equations, such as Bohr’s energy formula and Planck’s equation.
These principles explain the colors of light, the spectra of stars, the function of lasers, and many other real-world applications. Understanding how energy is absorbed and emitted allows scientists and engineers to develop advanced technologies in optics, electronics, and energy conversion.