Broken Pencil Demo

1
Broken Pencil Demo

• Is the pencil actually broken?
• Why does the pencil look like it is broken?
• Would we get the same effect without the water?

2
The light rays from the pencil travel from a
denser medium (water) to a less dense medium
(air). This makes the light ray refract away
from the normal, and the pencil is seen at the
extension of the refracted ray.
3
Refraction

• Light is observed to change directions as it
  crosses the boundary from one medium into another
  medium.
• The bending of the path of light is known as
  refraction.

4

• Light is refracted toward the normal as it enters
  a denser medium.
• Light is refracted away from the normal as it
  enters a less-dense medium.

5

• Angle of Refraction The angle which the
  refracted ray makes with the normal line

6
Snell's Law

• The study of the refraction of light as it
  crosses from one material into a second material
  yields a general relationship between the sines
  of the angle of incidence and the angle of
  refraction.
• This general relationship is expressed by the
  following equation
• angle of incidence
• angle of refraction
• ni index of refraction of the incident medium
• nr index of refraction of the refractive medium

7
Index of Refraction Value (n)

• Index of refraction values (represented by the
  symbol n) are numerical index values which are
  expressed relative to the speed of light in a
  vacuum

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Indices of Refraction
9
Example Problems

• In the following two examples, use Snell's law to
  complete the following diagrams

Given 45 degrees in Example A 60
degrees in Example B