PHYSICS 20B Lecture Notes - Lecture 9: Nuclear Fission, Helium Atom, Cno Cycle
Lecture 9
What Powers the Sun?
● What powers the Sun?
○ Albert Einstein suggested that a small amount of mass could be converted to a
very mass amount of energy, thus the famous equation
■ E = mc^2
○ 4 Hydrogen atoms have more mass than one Helium atom. Eddington pointed
out that the conversion of one element to another element could keep stars
burning for as long as Darwin required, because this conversion created energy.
■ The conversion of elements can create energy for stars
● Mass = Energy?
○ Mass is defined by an object’s resistance to acceleration
○ Law of Conservation of Mass
■ The initial and final product of a object, will always have the same mass
● For example, a glass of water will have the same mass as a if it
was frozen, or boiled (also measuring the water vapor)
■ And just like mass, energy also remains the same
● Water releases its locked up energy when boiled, no energy was
created, just released.
○ This is very important in explaining why conversion of
elements power stars
○ The only way we can tap into the energy of mass is through nuclear fusion, or
nuclear fission
● Nuclear fusion
○ Smaller atoms combine to form a more massive atoms.
○ Energy is released because the mass of the initial and final are different
■ Powers stars, modern nuclear bombs, prototype reactors (because it's
harder)
● Nuclear fission
○ Heavy atoms splits into lighter atoms.
○ Energy is released because the mass of the initial and final are different
■ Current nuclear power plants (because its easier)
● Atoms and Nuclei
○ Atoms contain protons (positive), neutrons (neutral), and electrons (negative)
○ Electrons determine the size, chemical reactions, and spectra of atoms
○ All atoms want be neutral (equal amount of neutrons and protons)
● Elements and Isotopes
○ The amount of protons determines the element
■ However there are similar elements but with different number of neutrons,
these elements are called isotopes
● Molecules
○ Groups of 2 or more atoms bonded together, (i.e. water molecules H20)
○ Primarily exist in cold gas, , the bonds break when exposed to heat (molecular
motion and temperature)
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Document Summary
Albert einstein suggested that a small amount of mass could be converted to a very mass amount of energy, thus the famous equation. 4 hydrogen atoms have more mass than one helium atom. Eddington pointed out that the conversion of one element to another element could keep stars burning for as long as darwin required, because this conversion created energy. The conversion of elements can create energy for stars. Mass is defined by an object"s resistance to acceleration. The initial and final product of a object, will always have the same mass. For example, a glass of water will have the same mass as a if it was frozen, or boiled (also measuring the water vapor) And just like mass, energy also remains the same. Water releases its locked up energy when boiled, no energy was created, just released. This is very important in explaining why conversion of elements power stars.
