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  3. Unit 1. optics
  4. The nature of light
  5. Refraction

1.3 Refraction

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By the end of this section, you will be able to:
  • Describe how rays change direction upon entering a medium
  • Apply the law of refraction in problem solving

You may often notice some odd things when looking into a fish tank. For example, you may see the same fish appearing to be in two different places ( [link] ). This happens because light coming from the fish to you changes direction when it leaves the tank, and in this case, it can travel two different paths to get to your eyes. The changing of a light ray’s direction (loosely called bending) when it passes through substances of different refractive indices is called refraction    and is related to changes in the speed of light, v = c / n . Refraction is responsible for a tremendous range of optical phenomena, from the action of lenses to data transmission through optical fibers.

Figure a shows a drawing of a person looking at the corner of a fish tank. A fish in the corner appears as a double image of the fish, one image formed by rays passing through each of the sides meeting at the corner of the tank. Figure b shows a photograph of a similar situation.
(a) Looking at the fish tank as shown, we can see the same fish in two different locations, because light changes directions when it passes from water to air. In this case, the light can reach the observer by two different paths, so the fish seems to be in two different places. This bending of light is called refraction and is responsible for many optical phenomena. (b) This image shows refraction of light from a fish near the top of a fish tank.

[link] shows how a ray of light changes direction when it passes from one medium to another. As before, the angles are measured relative to a perpendicular to the surface at the point where the light ray crosses it. (Some of the incident light is reflected from the surface, but for now we concentrate on the light that is transmitted.) The change in direction of the light ray depends on the relative values of the indices of refraction ( The Propagation of Light ) of the two media involved. In the situations shown, medium 2 has a greater index of refraction than medium 1. Note that as shown in [link] (a), the direction of the ray moves closer to the perpendicular when it progresses from a medium with a lower index of refraction to one with a higher index of refraction. Conversely, as shown in [link] (b), the direction of the ray moves away from the perpendicular when it progresses from a medium with a higher index of refraction to one with a lower index of refraction. The path is exactly reversible.

The figure is an illustration of the refraction of light at an interface between two media. In both figures, medium 1 is above medium 2 and the interface is horizontal and a ray is drawn refracting at the interface. . A line perpendicular to the interface is drawn at the point of incidence. In figure a, light is incident from above, passing from medium 1 to medium 2. In medium 1, the incident ray makes an angle of theta one to the perpendicular and the refracted ray in medium 2 makes a smaller angle theta two one to the perpendicular. In figure b, light is incident from below, passing from medium 2 to medium 1. In medium 2, the incident ray makes an angle of theta two to the perpendicular and the refracted ray in medium 1 makes a larger angle theta one to the perpendicular. Theta one in figure a is equal to the angle theta one in figure b. Likewise, theta two in figure a is equal to the angle theta two in figure b.
The change in direction of a light ray depends on how the index of refraction changes when it crosses from one medium to another. In the situations shown here, the index of refraction is greater in medium 2 than in medium 1. (a) A ray of light moves closer to the perpendicular when entering a medium with a higher index of refraction. (b) A ray of light moves away from the perpendicular when entering a medium with a lower index of refraction.

The amount that a light ray changes its direction depends both on the incident angle and the amount that the speed changes. For a ray at a given incident angle, a large change in speed causes a large change in direction and thus a large change in angle. The exact mathematical relationship is the law of refraction    , or Snell’s law , after the Dutch mathematician Willebrord Snell (1591–1626), who discovered it in 1621. The law of refraction is stated in equation form as

Questions & Answers

what is force
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The different examples for collision
Afework
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Muhammed Reply
Polarization is the process of transforming unpolarized light into polarized light. types of polarization 1. linear polarization. 2. circular polarization. 3. elliptical polarization.
Eze
Describe what you would see when looking at a body whose temperature is increased from 1000 K to 1,000,000 K
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how is tan ninety minus an angle equals to cot an angle?
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Jeremiah Reply
What is torque?
Matthew Reply
In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment, moment of force, rotational force or turning effect, depending on the field of study.
Teka
Torque refers to the rotational force. i.e Torque = Force × radius.
Arun
Torque is the rotational equivalent of force . Specifically, it is a force exerted at a distance from an object's axis of rotation. In the same way that a force applied to an object will cause it to move linearly, a torque applied to an object will cause it to rotate around a pivot point.
Teka
Torque is the rotational equivalence of force . So, a net torque will cause an object to rotate with an angular acceleration. Because all rotational motions have an axis of rotation, a torque must be defined about a rotational axis. A torque is a force applied to a point on an object about the axis
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n=I/r
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Mbah
Electrolysis is the chemical decomposition of electrolyte either in molten state or solution to conduct electricity
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Source:  OpenStax, University physics volume 3. OpenStax CNX. Nov 04, 2016 Download for free at http://cnx.org/content/col12067/1.4
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