ray tracing

Examples of ray tracing in the following topics:

• Thin Lenses and Ray Tracing

  • Ray tracing is the technique of determining the paths light rays take; often thin lenses (the light ray bending only once) are assumed.
  • Ray tracing is the technique of determining or following (tracing) the paths that light rays take.
  • For rays passing through matter, the law of refraction is used to trace the paths.
  • While ray tracing for complicated lenses, such as those found in sophisticated cameras, may require computer techniques, there is a set of simple rules for tracing rays through thin lenses.
  • Describe properties of a thin lens and the purpose of ray tracing

• The Thin Lens Equation and Magnification

  • Recall the five basic rules of ray tracing:
  • The figure shows three rays from the top of the object that can be traced using the five ray tracing rules.
  • It is best to trace rays for which there are simple ray tracing rules.
  • Ray tracing is used to locate the image formed by a lens.
  • Rays originating from the same point on the object are traced—the three chosen rays each follow one of the rules for ray tracing, so that their paths are easy to determine.

• Refraction Through Lenses

  • The expanded view of the path of one ray through the lens illustrates how the ray changes direction both as it enters and as it leaves the lens.
  • shows the effect of a concave lens on rays of light entering it parallel to its axis (the path taken by ray 2 in the figure is the axis of the lens).
  • In subsequent sections we will examine the technique of ray tracing to describe the formation of images by lenses.
  • The more powerful the lens, the closer to the lens the rays will cross.
  • Compare the effect of a convex lens and a concave lens on the light rays

• Refraction

  • For example, a light ray will refract as it enters and leaves glass, assuming there is a change in refractive index.
  • A ray traveling along the normal (perpendicular to the boundary) will change speed, but not direction.
  • This is due to the bending of light rays as they move from the water to the air.
  • Once the rays reach the eye, the eye traces them back as straight lines (lines of sight).
  • The lines of sight (shown as dashed lines) intersect at a higher position than where the actual rays originated (causing the pencil to appear higher and the water to appear shallower than they actually are).

• Nearsightedness, Farsidedness, and Vision Correction

  • The different parts of the eye have different refractive indexes, and this is what bends the rays to form an image.
  • This will cause the light rays to spread out before they enter the eye.
  • This will cause the light rays to slightly converge together before they enter the eye.
  • An image is formed on the retina with light rays converging most at the cornea and upon entering and exiting the lens.
  • Rays from the top and bottom of the object are traced and produce an inverted real image on the retina.

• X-Ray Spectra: Origins, Diffraction by Crystals, and Importance

  • In a previous Atom on X-rays, we have seen that there are two processes by which x-rays are produced in the anode of an x-ray tube.
  • In one process, the deceleration of electrons produces x-rays, and these x-rays are called Bremsstrahlung, or braking radiation.
  • The x-ray spectrum in is typical of what is produced by an x-ray tube, showing a broad curve of Bremsstrahlung radiation with characteristic x-ray peaks on it.
  • Thus, typical x-ray photons act like rays when they encounter macroscopic objects, like teeth, and produce sharp shadows.
  • The process is called x-ray diffraction because it involves the diffraction and interference of x-rays to produce patterns that can be analyzed for information about the structures that scattered the x-rays.

• Gamma Rays

  • Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency and therefore high energy.
  • Gamma rays have characteristics identical to X-rays of the same frequency—they differ only in source.
  • The distinction between X-rays and gamma rays has changed in recent decades.
  • Thus, gamma rays are now usually distinguished by their origin: X-rays are emitted by definition by electrons outside the nucleus, while gamma rays are emitted by the nucleus.
  • Identify wavelength range characteristic for gamma rays, noting their biological effects and distinguishing them from gamma rays

• X-Rays

  • X-radiation (composed of x-rays) is a form of electromagnetic radiation.
  • X-rays can be generated by an x-ray tube, a vacuum tube that uses high voltage to accelerate the electrons released by a hot cathode to a high velocity.
  • These x-rays have a continuous spectrum.
  • The intensity of the x-rays increases linearly with decreasing frequency, from zero at the energy of the incident electrons, the voltage on the x-ray tube.
  • Its unique features are x-ray outputs many orders of magnitude greater than those of x-ray tubes, wide x-ray spectra, excellent collimation, and linear polarization.

• X-Rays

  • They are shorter in wavelength than UV rays and longer than gamma rays.
  • X-rays with photon energies above 5 to 10 keV (below 0.2-0.1 nm wavelength), are called hard X-rays, while those with lower energy are called soft X-rays.
  • By contrast, soft X-rays are easily absorbed in air and the attenuation length of 600 eV (~2 nm) X-rays in water is less than 1 micrometer.
  • The distinction between X-rays and gamma rays is somewhat arbitrary.
  • Like all electromagnetic radiation, the properties of X-rays (or gamma rays) depend only on their wavelength and polarization.

• The Discovery of the Parts of the Atom

  • Thomson performed experiments demonstrating that cathode rays were unique particles, rather than waves, atoms or molecules, as was believed earlier.
  • Thomson made good estimates of both the charge $e$ and the mass $m$, finding that cathode ray particles (which he called "corpuscles") had perhaps one thousandth the mass of hydrogen, the least massive ion known.
  • After experimentation Rutherford traced the reaction to the nitrogen in air, and found that the effect was larger when alphas were produced into pure nitrogen gas.