The Sun is one of many billions of stars in the Milky Way. The Sun emits a very large quantity of energy as electromagnetic radiation.
(a) State the three regions of the electromagnetic spectrum in which the Sun emits the most energy.
(b) Electromagnetic radiation from the Sun travels at a speed of \(3.0 × 10^8\text{ m/s}\). The radiation takes \(500\text{ s}\) to reach the Earth. Calculate the distance from the Sun to the Earth.
(c) Approximately 4.6 billion years ago, the Sun formed from an interstellar cloud of gas and became a stable star.
(i) Describe and explain what happens as an interstellar cloud of gas forms a protostar.
(ii) Describe and explain what happens as a protostar becomes a stable star.
Correct Answer: ultraviolet AND visible light AND infrared only
Detailed solution: The Sun is a medium-sized star that radiates energy across the entire electromagnetic spectrum, but its peak energy output is concentrated in three main regions: ultraviolet, visible light, and infrared. Any inclusion of other regions (like X-rays or radio waves) in this specific list would be considered an incorrect addition.
Correct Answer: \(1.5 \times 10^{11}\text{ m}\)
Detailed solution: Distance is calculated by rearranging the speed equation \(v = s/t\) to \(s = v \times t\). Substituting the given values: speed \(v = 3.0 \times 10^8\text{ m/s}\) and time \(t = 500\text{ s}\). Multiplying these gives \(3.0 \times 10^8 \times 500 = 1.5 \times 10^{11}\text{ m}\), which is the distance from the Sun to Earth.
Correct Answer: The cloud/nebula collapses due to (internal) gravitational attraction, and the (internal) temperature increases.
Detailed solution: A protostar forms when an interstellar cloud of gas and dust (nebula) begins to collapse under its own internal gravitational attraction. As the material is pulled inward, gravitational potential energy is converted to kinetic energy, causing the density and the internal temperature of the collapsing core to rise significantly.
Correct Answer: Nuclear fusion / nuclear reactions occur; the inward gravitational force is balanced by an outward force due to the high temperature.
Detailed solution: A protostar becomes a stable star when the core temperature and pressure become high enough to initiate nuclear fusion (converting hydrogen to helium). The star reaches stability when the inward force of gravitational attraction is exactly balanced by the outward force created by the immense pressure from the high internal temperature generated by these nuclear reactions.
