Please provide a rating, it takes seconds and helps us to keep this resource free for all to use
Welcome to our Physics lesson on The Source of Solar Energy, this is the second lesson of our suite of physics lessons covering the topic of Sun and Planetary Motion, you can find links to the other lessons within this tutorial and access additional physics learning resources below this lesson.
The question that has intrigued many scientists for centuries was: "What is the source of solar energy?" It was only in the last century (by the end of 1930s) that scientists realized that all this energy is produced by means of nuclear reactions of fusion (as discussed in tutorial 20.4). Such reactions occur in the innermost part of the Sun called the "Sun core". It is a spherical-shaped region with a radius not more than 1/5 of the Sun's radius.
Because of enormous pressure exerted by upper layers, the temperature of the Sun's core reaches 10-15 million Celsius degree. The Sun's core density is more than 100 times higher than water density. This is because electrons have been removed from atoms when reducing resulting in empty spaces that exist in cold (normal) atoms. In these conditions, hydrogen nuclei (i.e. protons) have very small distances between them, resulting in the perfect conditions for nuclear fusion to occur. In fact, there is not a single type of nuclear reaction involved in this process but a number of nuclear reactions forming the proton-proton (p-p) reaction chain. From Section 21 it is undestood that the reactions which convert hydrogen to helium are accompanied by the release of large amounts of energy. In this way, the Sun's hydrogen acts like a "nuclear fuel" while the helium produced is like the "ash" produced after a burning process.
The composition of the Sun consists of 71% hydrogen and 27% helium. The remaining 2% consists of other chemical elements. The amount of hydrogen decreases and that of helium (and heavier elements) increases with time.
In one of the p-p reactions in the aforementioned chain, the weak interaction is involved - a process that brings the emission of an electronic neutrino. In Section 21 we learned that these reactions have a low probability of occuring. This is why hydrogen is consumed very slowly and the Sun produces energy at the same rate for several billions of years.
You have reached the end of Physics lesson 22.2.2 The Source of Solar Energy. There are 10 lessons in this physics tutorial covering Sun and Planetary Motion, you can access all the lessons from this tutorial below.
Enjoy the "The Source of Solar Energy" physics lesson? People who liked the "Sun and Planetary Motion lesson found the following resources useful:
Please provide a rating, it takes seconds and helps us to keep this resource free for all to use
We hope you found this Physics lesson "Sun and Planetary Motion" useful. If you did it would be great if you could spare the time to rate this physics lesson (simply click on the number of stars that match your assessment of this physics learning aide) and/or share on social media, this helps us identify popular tutorials and calculators and expand our free learning resources to support our users around the world have free access to expand their knowledge of physics and other disciplines.