refraction

Examples of refraction in the following topics:

• Refraction

  • In optics, refraction is a phenomenon that often occurs when waves travel from a medium with a given refractive index to a medium with another at an oblique angle.
  • For example, a light ray will refract as it enters and leaves glass, assuming there is a change in refractive index.
  • Refraction still occurs in this case.
  • Understanding of refraction led to the invention of lenses and the refracting telescope.
  • Air has a refractive index of about 1.0003, and water has a refractive index of about 1.33.

• The Law of Refraction: Snell's Law and the Index of Refraction

  • Refraction: The changing of a light ray's direction (loosely called bending) when it passes through variations in matter is called refraction.
  • In mediums that have a greater index of refraction the speed of light is less.
  • The incoming ray is called the incident ray and the outgoing ray the refracted ray, and the associated angles the incident angle and the refracted angle.
  • Snell's experiments showed that the law of refraction was obeyed and that a characteristic index of refraction n could be assigned to a given medium.
  • Formulate the relationship between the index of refraction and the speed of light

• Dispersion: Rainbows and Prisims

  • The angle of refraction depends on the index of refraction, as we saw in the Law of Refraction.
  • We know that the index of refraction n depends on the medium.
  • Rainbows are produced by a combination of refraction and reflection.
  • The light is refracted both as it enters and as it leaves the drop.
  • Since the index of refraction varies with wavelength, the angles of refraction vary with wavelength.

• Dispersion of the Visible Spectrum

  • Rainbows are not only caused by refraction, like prisms, but also reflection.
  • The light is refracted once as it enters the drop, and again as is exits the drop.
  • In water, the refractive index varies with wavelength, so the light is dispersed.
  • Since the index of refraction varies with wavelength, the angles of refraction vary with wavelength.
  • This light is refracted and dispersed both as it enters and as it leaves the drop.

• Polarization By Scattering and Reflecting

  • When light hits a reflective surface, the vertically polarized aspects of that light are refracted at that surface.
  • If the arrow hits the target perpendicularly (vertically polarized), it is going to stick in the target (be refracted into the surface).
  • Since the light is split into two, and part of it is refracted, the amount of polarization to the reflected light depends on the index of refraction of the reflective surface.
  • where: θb = angle of reflection of complete polarization (also known as Brewster's angle); n1 = index of refraction of medium in which reflected light will travel; and n2 = index of refraction of medium by which light is reflected.
  • Calculate angle of reflection of complete polarization from indices of refraction

• The Telescope

  • The first telescope was a refracting telescope made by spectacle makers in the Netherlands in 1608.
  • After the refracting telescope was invented, people began to explore the idea of a telescope that used mirrors.
  • The figure above is a diagram of a refracting telescope.
  • The objective lens refracts, or bends, light.
  • All refracting telescopes use the same principles.

• Refraction Through Lenses

  • Because the index of refraction of a lens is greater than air, a ray moves towards the perpendicular as it enters and away as it leaves.
  • Since the index of refraction of the lens is greater than that of air, the ray moves towards the perpendicular as it enters, and away from the perpendicular as it leaves (this is in accordance with the law of refraction).
  • The expanded view of the path of one ray through the lens illustrates how the shape of the lens (given the law of refraction) causes the ray to follow its particular path and be diverged.

• Aberrations

  • This happens because lenses have a different index of refraction for different wavelengths of light.
  • The refractive index decreases with increasing wavelength.
  • Since the index of refraction of lenses depends on color or wavelength, images are produced at different places and with different magnifications for different colors. shows chromatic aberration for a single convex lens.
  • Since violet rays have a higher refractive index than red, they are bent more and focused closed to the lens. shows a two-lens system using a diverging lens to partially correct for this, but it is nearly impossible to do so completely.
  • Different parts of a lens of a mirror do not refract or reflect the image to the same point, as shown in .

• The Ray Aspect of Light

  • The law that deals with this change in direction is called the law of refraction.
  • This change in ray direction will depend on the refractive index of the material through which the light is travelling.
  • This is because the index of refraction of the water is different from that of the air.
  • The concept of refraction explains how a pencil submerged in water appears to bend.

• Total Internal Reflection and Fiber Optics

  • If the refractive index is lower on the other side of the boundary and the incident angle is greater than the critical angle, the wave cannot pass through and is entirely reflected.
  • The angle of incidence is measured with respect to the normal at the refractive boundary (see diagram illustrating Snell's law).
  • Here, n1 and n2 are refractive indices of the media, and $\theta_1$ and $\theta_2$are angles of incidence and refraction, respectively.
  • The difference in refractive index of the cladding and the core allows total internal reflection in the same way as happens at an air-water surface show in .
  • Refraction of light at the interface between two media, including total internal reflection.