Understanding Classical Physics Limitations and Modern Concepts
Limitations of Classical Physics
Classical mechanics, based on Galilean transformations and Newton’s equations, faced challenges with Maxwell’s equations. These equations confirmed the wave nature of light and allowed for the calculation of its speed in a vacuum, leading to comparisons between light and sound waves.
Characteristics of Sound
- Requires a medium to propagate.
- Propagates at a steady pace with respect to the medium.
- Velocity can be found using the formula for the addition of velocities.
Characteristics of Light
Early theories proposed a medium called ‘ether’ for light propagation, suggesting light propagates with a fixed speed relative to the ether. However, this hypothesis required the existence of a massless and elastic substance, the ether, and a reference system for electromagnetism.
Einstein’s Postulates
Einstein’s special theory of relativity, applicable to all physical phenomena, is based on two postulates:
Postulate 1:
The laws of physics are the same in all inertial reference systems. This generalizes the principle of Galilean relativity, which only applied to mechanics. The laws of physics must remain invariant when transitioning between inertial systems.
Postulate 2:
The speed of light is the same in all reference systems, regardless of the source’s velocity. This invalidates Galilean transformations.
Nuclear Reactions
Fission
Nuclear fission is a reaction where a heavy nucleus splits into two lighter nuclei when bombarded by neutrons. This process releases more neutrons and a significant amount of energy.
Fusion
Nuclear fusion is a reaction where two light nuclei combine to form a heavier nucleus, also releasing energy. Both fission and fusion require activation energy.
Radiation
Alpha Radiation
Alpha radiation consists of helium nuclei (two protons and two neutrons) emitted with kinetic energy in MeV.
Beta Radiation
Beta radiation consists of fast electrons or positrons originating from neutron disintegration in the nucleus, giving rise to a proton and an electron. Measured in MeV.
Gamma Radiation
Gamma radiation is electromagnetic radiation with higher frequency than X-rays, with energies between KeV and MeV.
Radiation Hazards to Humans
External Sources:
Alpha, Beta, and Gamma radiation.
Internal Sources:
Gamma, Beta, and Alpha radiation.
Measuring Radiation Effects
Absorbed Dose:
Absorbed energy per unit of mass, measured in Gray (Gy).
Equivalent Dose:
The product of the absorbed dose and the coefficient of relative biological effectiveness, measured in Sievert (Sv).
Fundamental Forces
Strong Nuclear Force:
Responsible for the cohesion of the nucleus, manifesting as an attractive force between nucleons. It is negligible beyond 10^-15 meters and the strongest force at short distances.
Weak Nuclear Force:
Responsible for the beta decay of nuclei, affecting particles not subject to strong nuclear forces. It is negligible beyond 10^-17 meters and weaker than gravity at short distances.
Gravitational Force:
Acts between any two particles with mass. It is always attractive and a weak interaction, noticeable only when an object has significant mass.
Electromagnetic Force:
Acts between electrically charged particles. It can be attractive or repulsive and is stronger than the gravitational force. At distances greater than 10^-15 meters, it is stronger than the strong nuclear force.