Light and the electromagnetic spectrum Study Guide

The Earth's global average temperature is determined by a delicate balance between the energy received from the Sun, primarily as short-wavelength visible and ultraviolet radiation, and the energy radiated back into space as longer-wavelength infrared radiation. Approximately 30% of incoming solar radiation is reflected directly back into space by clouds, ice, snow, and the Earth's surface. The remaining 70% is absorbed by the Earth's surface and atmosphere. This absorbed energy warms the planet, leading to its emission of infrared radiation. Greenhouse gases in the atmosphere, such as carbon dioxide, methane, and water vapour, absorb some of this outgoing infrared radiation, preventing it from escaping directly into space. This absorption and re-emission of infrared radiation by greenhouse gases is known as the greenhouse effect, which naturally warms the Earth to a habitable temperature. Any alteration to the amount of incoming solar radiation (e.g., changes in solar output, variations in Earth's orbit) or the Earth's reflectivity (albedo, e.g., due to changes in ice cover or cloud formation), or changes in the concentration of atmospheric greenhouse gases, will perturb this energy balance and consequently impact the Earth's temperature.

Changes within atoms and atomic nuclei are fundamental processes in physics that can both generate and be caused by electromagnetic radiation. When electrons within an atom move from a higher energy level to a lower one, or when atomic nuclei undergo decay or fusion, they emit energy in the form of electromagnetic radiation. This radiation can span a broad spectrum of frequencies, including visible light, X-rays, and gamma rays, depending on the energy involved in the transition. Conversely, atoms and nuclei can absorb electromagnetic radiation. When an atom absorbs a photon with sufficient energy, an electron can jump to a higher energy level. When a nucleus absorbs a high-energy photon or particle, it can become unstable, potentially leading to nuclear reactions or changes in its state.