SAT Physics Historical Figures and Contemporary Physics - Historical Figures

SAT Physics Historical Figures and Contemporary Physics - Historical FiguresHISTORICAL FIGURES
Newtonian Mechanics
Bodies dropped from the same height will all fall with the same acceleration, g. The distance they travel is proportional to the square of time, y = Principle of inertia: The natural state of motion is uniform constant velocity.ISAAC NEWTON (1642-1727)
1st law of motion (law of inertia): Modifies Galileo’s principle of inertia. The natural state of motion is constant velocity unless acted upon by an unbalanced force.2nd law of motion (ΣF = ma): The acceleration of an object is directly proportional to the net force acting on the object. Acceleration is inversely proportional to the mass of the object.3rd law of motion: When two objects interact (action-reaction pair), an equal and oppo­site force acts on each object. This causes an opposite reaction. However, the actual motion depends on the masses involved.Law of gravity (Fg = Gm1m2/r2): Two masse…

SAT Physics Relativity - Special Theory Of Relativity

SAT Physics Relativity - Special Theory Of RelativitySPECIAL THEORY OF RELATIVITY
Until Einstein’s paper in 1905, most physicists believed that the universe was filled with an invisible medium called ether. They reasoned that ether was necessary in order for light, considered by most physicists to be a wave, to propagate through space. However, experiments such as the famous Michelson-Morley experiment all failed to prove the existence of ether.
    Einstein viewed the problem in a completely different manner and proposed an explanation for these failed experiments. He viewed light as a quantum particle (later named a photon) that traveled with a specific speed in a vacuum, c = 3 × 108 meters per second. Einstein then suggested that the speed of light is the same for all inertial reference frames.An inertial reference frame is a frame of reference moving at a constant velocity. (Inertia is the tendency of objects to continue moving at constant velocity.) Einstein stated that the speed o…

SAT Physics Nuclear Reactions - Radioactive Decay

SAT Physics Nuclear Reactions - Radioactive DecayRADIOACTIVE DECAY
Radioactive decay occurs when an unstable isotope spontaneously loses energy by emitting particles from its nucleus. The decay processes were named in their order of discovery by using the first three letters of the Greek alphabet: alpha (α), beta (β), and gamma (γ). After their initial discovery, it was determined that an alpha particle was in fact the nucleus of a helium atom , a beta particle was actually an electron, , and gamma radiation was not a particle at all. Instead, it is a high-frequency photon, . Elements that naturally decay are said to be radioactive. Radioactive substances have a critical imbalance between the number of protons and neutrons in the nucleus. As atoms become larger, more neutrons are needed to maintain stability. Uranium-235 has 92 protons and 143 neutrons. The three common forms of natural radioactivity—alpha, beta, and gamma radiation—are discussed below.

Alpha Decay
In an alpha decay, an…

SAT Physics Nuclear Reactions - Nucleons

SAT Physics Nuclear Reactions - NucleonsNUCLEONS
Nuclear reactions are concerned with the nucleus of the atom and the particles it contains. The subatomic particles contained in the nucleus of an atom are known as nucleons. They consist of protons and neutrons. Both the mass and the number of these particles are important when analyzing nuclear reactions.

Atomic Mass Units
A specialized unit of mass known as the atomic mass units (u) was devised to make working with the mass, of fundamental particles easier. The mass of both the proton and neutron were originally thought to be the same. They were each assigned a mass of 1.0 atomic mass unit for simplicity. It has since been determined that the masses are very similar but that the neutron has a slightly greater mass. The modern definition of an atomic mass unit is the mass of a carbon-12 atom. By using this scale, a proton has a mass of 1.00728 atomic mass units while a neutron has a mass of 1.00866 atomic mass units. For rough calculati…

SAT Physics Atomic and Quantum Phenomena - Ionization Energy/Work Function

SAT Physics Atomic and Quantum Phenomena - Ionization Energy/Work FunctionIONIZATION ENERGY/WORK FUNCTION
In energy level problems, electrons receive just enough energy to reach a higher energy level inside the atom. However, if the energy of the incoming photons is greater than the energy difference between the ground state and the edge of the atom, then the electrons are ejected from the atom. In this process, the atom becomes a positive ion. The minimum energy required to accomplish this is known as the ionization energy. For atoms with electrons in the ground state, the ionization energy is equal to the absolute value of the ground state energy. For hydrogen gas with a ground state of -13.6 electron volts, the ionization energy is equal to 13.6 electron volts. The ionization energy is the minimum energy needed to eject an electron and ionize an atom. The ionization energy is also known as the work function, Φ.

The photoelectric effect involves the ionization of a…

SAT Physics Atomic and Quantum Phenomena - Development Of The Atomic Theory

SAT Physics Atomic and Quantum Phenomena - Development Of The Atomic TheoryDEVELOPMENT OF THE ATOMIC THEORY
The ancient Greeks first proposed the word "atom” as the name for an indivisible unit of matter. Several observations and prominent experiments have led to a greater understanding of atoms. The following sections include major highlights and scientists involved in development of the atomic theory.

J. J. Thomson
In 1897, J. J. Thomson discovered that even atoms themselves were divisible when he discovered the electron. Thomson knew that matter had an overall neutral charge, so he theorized that an atom of matter would be a mixture of positive and negative components.His model, often referred to as the “raisin cake model” or “plum-pudding model,” visualized the atom as containing positive and negative charges that were distributed throughout the interior of the atom.

Figure 20.1. Plum pudding model of an atom
Ernest Rutherford
Ernest Rutherford, a student of Thomson’s, began to exp…