Key Physics Concepts and Fundamental Forces

Magnetic Resonance Imaging Principles

11. How MRI Works: It uses the body's natural magnetic properties to produce detailed images from any part of the body. An MRI scanner applies a very strong magnetic field (about 0.2 to 3 teslas, or roughly a thousand times the strength of a typical fridge magnet), which aligns the proton "spins."

The Four Fundamental Forces of Nature

12. Fundamental Forces: Particles and Distance

(A force which cannot be explained in terms of other forces)

Force, State Particles, Relative Strength, Distance

• Gravity: Graviton (conjectured) / 10^-38 / Range: Infinity
• Electromagnetic: Photon (observed) / 10^-2 / Range: Infinity
• Weak Force: W⁺, W^-, Z⁰ (observed) / 10^-13 / Range: < 10^-18m
• Strong Force: Gluons (conjectured) / 1 / Range: < 10^-15m

Radiation Shielding and Particle Penetration

13. What can stop beta particles, alpha particles, X-rays, and gamma rays?

• Alpha: Cardboard
• Beta: Aluminum
• Gamma: Lead
• X-Ray: Lead

Understanding the Inverse Square Law

14. Inverse Square Law: A law stating that the intensity of an effect, such as illumination or gravitational force, changes in inverse proportion to the square of the distance from the source. The electromagnetic force has a strength proportional to the product of the electric charges of the particles and inversely proportional to the square of the distance between the particles' centers of mass.

Refraction and Optical Lens Applications

15. Refraction: The phenomenon of light, radio waves, etc., being deflected in passing obliquely through the interface between one medium and another or through a medium of varying density. The most common application of refraction is in the field of optics. A lens is a transparent material that refracts light rays to converge at a single point. Lenses are designed in such a manner that light entering them is focused by refraction into a focal point, producing a magnified image of an object.

The Doppler Effect in Sound and Light

16. Doppler Effect: An increase (or decrease) in the frequency of sound, light, or other waves as the source and observer move toward (or away from) each other. When the sound is approaching you, the frequency is increasing. When it is going away, the frequency is decreasing. Application: The siren on a passing emergency vehicle will start out higher than its stationary pitch, slide down as it passes, and continue lower than its stationary pitch as it recedes from the observer.