Question

fusion & energy from the sun – guided notes
learning target
i can explain why fusion releases energy and how that energy reaches earth.
success criteria

• i can explain why fusion releases energy.
• i can use ( e = mc^2 ) to describe mass - energy conversion.
• i can describe how solar energy travels to earth as light and heat.

vocabulary

• mass defect
• binding energy
• ( e = mc^2 )
• electromagnetic radiation

• why fusion releases energy

fusion produces energy because:

• nuclei of hydrogen combine to form ______.
• the mass of the helium nucleus is ______ than the total mass of the original protons.
• this “missing” mass is converted to ______ (called the mass defect).
• the difference comes from ______ energy (the force that holds protons and neutrons together).

• predicting the energy – ( e = mc^2 )

einstein’s equation shows:

• ( e = mc^2 ) means ____ and ____ are two forms of the same thing.
• a small mass can release a ______ amount of energy because ( c^2 ) is a very large number.
• example: ( 4 h \to he ) releases about ______ mev (million electron volts).

• how energy escapes the sun
• fusion makes high - energy ______ rays in the core.
• photons in the radiative zone take a “random walk” — constantly ____ and ____.
• this can take ____ to ____ of years for energy to reach the surface.
• in the convective zone, hot gases carry energy outward by ______.
• at the photosphere, photons finally escape as mostly ____, __, and ____ light.
• from there it takes only ______ minutes to reach earth.

• what we experience on earth
• visible light → lets us ______ and warms surfaces when absorbed.
• infrared (ir) → we feel this as ______ on our skin right away.
• ultraviolet (uv) → higher energy, can ______ skin cells (we’ll discuss tomorrow).

Explanation:

To solve the fill - in - the - blanks in these guided notes about fusion and solar energy, we rely on the fundamental concepts of nuclear physics and solar energy transfer:

Why Fusion Releases Energy

• When hydrogen nuclei undergo fusion, they combine to form a helium nucleus. This is a basic fact of the proton - proton chain reaction which is the main fusion process in the Sun.
• According to the principle of mass - energy equivalence ($E = mc^{2}$), the mass of the helium nucleus is less than the sum of the masses of the original protons. This is because some mass is converted into energy during the fusion process.
• The “missing” mass is converted into energy (this is what the mass defect refers to). The mass defect is the difference between the mass of the reactants and the mass of the products in a nuclear reaction, and this mass is transformed into energy.
• The source of this energy difference is binding energy. Binding energy is the energy that is required to separate the protons and neutrons in a nucleus, and it is related to the mass defect.

Predicting the Energy - $E = mc^{2}$

• Einstein's equation $E=mc^{2}$ tells us that mass and energy are two forms of the same entity. Mass can be converted into energy and vice versa.
• Since $c$ (the speed of light) is a very large number, when we square it ($c^{2}$), a small mass can release a large amount of energy.
• In the fusion reaction $4\mathrm{H}\to\mathrm{He}$, approximately 26.7 MeV of energy is released. This is a well - known value for the energy released in the proton - proton chain reaction that forms helium from hydrogen.

How Energy Escapes the Sun

• Fusion in the Sun's core produces high - energy gamma rays. Gamma rays are a form of electromagnetic radiation with very high energy.
• In the radiative zone of the Sun, photons (including gamma rays that are gradually transformed) take a “random walk”. This means they are constantly absorbed and re - emitted as they interact with the particles in the radiative zone.
• The time it takes for energy to travel from the core to the surface of the Sun through the radiative and convective zones can be from thousands to millions of years.
• In the convective zone, hot gases carry energy outward by the process of convection. Convection is the transfer of heat through the movement of a fluid (in this case, the hot solar gas).
• At the photosphere, the photons finally escape as mostly visible, infrared, and ultraviolet light. These are different parts of the electromagnetic spectrum that the Sun emits.
• Once the photons leave the photosphere, it takes only about 8 minutes for the light (and the energy it carries) to reach the Earth.

What We Experience on Earth

• Visible light allows us to see and also warms surfaces when it is absorbed. This is a basic function of visible light in our daily experience.
• Infrared (IR) radiation is what we feel as heat on our skin almost immediately. Infrared radiation is associated with thermal energy.
• Ultraviolet (UV) radiation has higher energy and can damage skin cells. This is why we need protection from excessive UV exposure, as it can cause sunburn, skin aging, and an increased risk of skin cancer.

Answer:

s (filling in the blanks):

• Nuclei of hydrogen combine to form $\boldsymbol{\text{helium nucleus}}$.
• The mass of the helium nucleus is $\boldsymbol{\text{less}}$ than the total mass of the original protons.
• This “missing” mass is converted to $\boldsymbol{\text{energy}}$ (called the mass defect).
• The difference comes from $\boldsymbol{\text{binding}}$ energy (the force that holds protons and neutrons together).
• $E = mc^{2}$ means $\boldsymbol{\text{mass}}$ and $\boldsymbol{\text{energy}}$ are two forms of the same thing.
• A small mass can release a $\boldsymbol{\text{large}}$ amount of energy because $c^{2}$ is a very large number.
• Example: $4\mathrm{H}\to\mathrm{He}$ releases about $\boldsymbol{26.7}$ MeV (million electron volts).
• Fusion makes high - energy $\boldsymbol{\text{gamma}}$ rays in the core.
• Photons in the radiative zone take a “random walk” — constantly $\boldsymbol{\text{absorbed}}$ and $\boldsymbol{\text{re - emitted}}$.
• This can take $\boldsymbol{\text{thousands}}$ to $\boldsymbol{\text{millions}}$ of years for energy to reach the surface.
• In the convective zone, hot gases carry energy outward by $\boldsymbol{\text{convection}}$.
• At the photosphere, photons finally escape as mostly $\boldsymbol{\text{visible}}$, $\boldsymbol{\text{infrared}}$, and $\boldsymbol{\text{ultraviolet}}$ light.
• From there it takes only $\boldsymbol{8}$ minutes to reach Earth.
• Visible Light $\to$ lets us $\boldsymbol{\text{see}}$ and warms surfaces when absorbed.
• Infrared (IR) $\to$ we feel this as $\boldsymbol{\text{heat}}$ on our skin right away.
• Ultraviolet (UV) $\to$ higher energy, can $\boldsymbol{\text{damage}}$ skin cells (we'll discuss tomorrow).