Fundamental Forces & Quantum Physics Principles
Radioactivity: Biological Effects & Applications
For millions of years, living things have withstood the natural radioactivity of the Earth’s crust and cosmic rays. Exposure to high doses of radiation at increased rates can cause cancer and other genetic disorders. The degree of danger of an isotope depends on the type of radiation emitted, its energy, and its half-life.
Degree of Danger to Humans:
- External Exposure: If the radiation source is outside the body, gamma rays are the most dangerous. However, alpha particles do not penetrate beyond the skin.
- Internal Exposure: If the source is inside the body, alpha particles are the most dangerous due to their short range and greater mass.
Nuclear Forces
- Strong Nuclear Force: Responsible for the cohesion of the nucleus. It is an attractive force between nucleons, manifesting irrespective of their electrical charge. It is of great significance. At very short distances, it is superior to any other force.
- Weak Nuclear Force: Responsible for causing the beta decay of nuclei. It manifests mainly in particles not subject to the action of the strong nuclear force. It is of great significance. At very short distances, its maximum intensity exceeds the gravitational force.
Fundamental Forces
- Gravitational Force: Exerted between two particles with mass. It is always attractive and is a weak interaction, only noticeable when one of the bodies has a large mass.
- Electromagnetic Force: Exerted between two electrically charged particles. It can be attractive or repulsive and is of greater intensity than the gravitational force.
- Strong Nuclear Force: Responsible for the cohesion of the nucleus, binding nucleons together. It is a very strong interaction at nuclear distances and has a short range.
- Weak Nuclear Force: Responsible for the beta decay of some unstable nuclei. It is weaker than the strong nuclear and electromagnetic forces and has a short range.
Quantum Mechanics
Two key features of quantum mechanics are wave-particle duality and the uncertainty principle.
Wave-Particle Duality (De Broglie Hypothesis)
French physicist Louis de Broglie suggested that electrons could have wave characteristics. This became known as the de Broglie hypothesis. Under this scenario, both the energy (E) and the radiation field are related to the frequency (f) of the wave:
E = hf
And the momentum (p) with the wavelength (λ):
p = E / c = hf / c, so p = h / λ
Thus, the wavelength (λ) associated with a material particle or a photon of momentum (p) is:
λ = h / p, or λ = h / mv
However, experimental evidence was lacking. British physicists confirmed the relationship derived theoretically by de Broglie (λ = h / p) through the diffraction of electron beams.
The Double-Slit Experiment
This experiment involves firing electrons, one by one, from a source (S) towards a pair of slits. The arrival of each electron is recorded on a photographic plate on screen (P). All electrons are released with the same speed and with the same wavelengths. Although we cannot predict where each individual electron will collide, after the impact of many electrons, a wave interference pattern appears. The pattern obtained is identical to that observed in the case of photons of the same wavelength.
Heisenberg’s Uncertainty Principle
According to classical physics, the error in a measurement is due to the imprecision of the measuring apparatus. Werner Heisenberg questioned this assumption. He enunciated his principle of indeterminacy, or uncertainty principle, which provides limits to the information we can obtain about a quantum object. This principle has two parts:
- It is not possible to simultaneously determine the exact value of the x, y position and the momentum (p) of a quantum object. A high degree of accuracy in the value of the position is equivalent to a large uncertainty in the measurement of the momentum.
- It is not possible to simultaneously determine the measured value of the energy (E) of a quantum object and the length of time required to take measurements.