Ch 3 · 6.2.1 The Sun as a Star · O Level Physics 5054
Topic 3 of 5 in Space Physics — O Level Physics 5054 — 19 lessons.
Introduction
The Sun looks special to us because it is so close, but it is an ordinary star, one of billions in our galaxy. It has been shining steadily for about 4.6 billion years. (Syllabus section 6.2.1.)
Key ideas
The Sun emits electromagnetic radiation across the spectrum, but it radiates most of its energy in three regions:
🧑🏫 Teacher's explanation
Imagine a massive, glowing furnace floating in space. This furnace isn't burning wood or coal; instead, it is a giant ball of gas where the atoms are being squeezed together so hard that they actually merge. This process is like taking two small pieces of modeling clay and smashing them together to make one larger piece, releasing a huge burst of heat and light in the process.
📖 Definitions
🔍 Worked example — Easy
The Sun radiates energy primarily in three regions. List these three regions of the electromagnetic spectrum in order of increasing wavelength.
🔍 Worked example — Standard
A star's core temperature is 1.5 × 10^7 K. If the star is stable, what specific nuclear reaction is occurring in the core?
🔍 Worked example — Exam-style
The Sun consists of approximately 75\% hydrogen and 25\% helium by mass. If a sample of solar matter has a total mass of 4.0 × 10^30 kg, calculate the mass of hydrogen present.
⚠️ Common errors
🧠 Quick check 1
🧠 Quick check 2
🎯 Exam question
(a) State the two main elements that make up the Sun. [2] (b) Describe the nuclear reaction that powers the Sun. [2] [4 marks]
Worked example
In the Sun's core, the temperature and pressure are extremely high. Hydrogen nuclei fuse to form helium nuclei. This nuclear fusion releases a large amount of energy, which travels out through the Sun and is radiated, mostly as infrared, visible and ultraviolet radiation.
🔍 Worked example — Easy
Identify the primary elements that make up the Sun and the process that powers it.
🔍 Worked example — Standard
A star radiates energy across the electromagnetic spectrum. List the three specific regions where the Sun radiates most of its energy.
🔍 Worked example — Exam-style
In a simplified model, a single fusion reaction converts a mass of 4.0 × 10^-30 kg of hydrogen into a helium nucleus with a mass of 3.9 × 10^-30 kg. Calculate the mass defect Δ m and state the type of reaction occurring.
⚠️ Common errors
Common mistakes
Practice
Answers: (1) Hydrogen and helium. (2) Infrared, visible and ultraviolet. (3) The fusion of hydrogen into helium.