Final answer:
Nuclear fusion is the process where two light atomic nuclei combine to form a heavier nucleus, releasing significant energy. It is the reaction that powers the sun and has potential as a sustainable energy source.
Step-by-step explanation:
The combining of two isotopes of a light element such as hydrogen to form a heavier nucleus, which releases energy in the process, is called nuclear fusion. In nuclear fusion, the nuclei of light atoms such as hydrogen combine to form a new, heavier element. An example of a fusion reaction in stars like our sun includes the formation of helium from hydrogen isotopes. The proton-proton cycle, a common fusion reaction in stars, involves hydrogen nuclei fusing together to eventually form helium, with significant energy released in the form of light and heat. Remarkably, the energy produced by nuclear fusion powers the sun and many other stars.
Fusion is a key area of research for developing sustainable and powerful energy sources, as the process releases a considerable amount of energy. Typically, hydrogen isotopes are used in fusion reactions to form helium nuclei. In the process, mass is converted into energy as dictated by Einstein's equation, E=mc^2, releasing a large amount of energy that can, in theory, be harnessed for practical use. The conditions required for nuclear fusion—extremely high temperatures and pressures—are difficult to achieve and maintain on Earth, making it a challenge for it to become a practical energy source at this time.