Geometric Optics TEST: 12 April 2016

The Law of Reflection

Reflection Light behaves in a very predictable manner Light can only travel in a straight line (most of the time…) The Law of Reflection states that the INCIDENT (incoming) light’s angle will be exactly the same as the reflecting light’s angle

Reflection This angle is always measured from an imaginary line Perpendicular to the plane of the mirror This will be of more importance when we discuss curved or spherical mirrors

Reflection All objects reflect light Not all objects produce an image Specular Reflection: occurs on smooth surfaces, all light reflects at the same angle (since it strikes the surface at the same angle), produces a clear image

Reflection Diffuse reflection: occurs on rough surfaces, light scatters (as the incident light will hit the surface at many different angles), produces blurry, unclear, or no image at all

Types of materials Transparent: completely see-through Translucent: See-through, cloudy Opaque: Cannot see through

Refraction and Snell’s Law Quiz tomorrow!!

Refraction When light (or any wave) reaches a boundary between two mediums, refraction occurs As the wave changes medium, its speed changes due to a change in density of the medium This causes the light to bend, or change course

Refraction and sight As light travels, it moves in a straight line When it changes medium, refraction can bend that straight line slightly This is why objects in water tend to have distorted images and position Our eyes and brains assume the light have traveled in a straight line

Index of Refraction How much light speeds up or slows down depends on density The denser the medium, the slower the speed The index of refraction is a ratio that relates the new speed to the speed of light in a vacuum, which is constant

Indices of Refraction

Bending The direction the light bends is always related to the normal More dense to less dense: Light moves faster, light bends AWAY from the normal Less dense to more dense: light moves slower, light Bends toward the normal

Snell’s Law We can relate the two materials using snell’s law, in order to find the refracted angle

Example: Light travels from air into an optical fiber with an index of refraction of 1.44.  (a)  In which direction does the light bend?  (b)  If the angle of incidence on the end of the fiber is 22o, what is the angle of refraction inside the fiber?  (c)  Sketch the path of light as it changes media.

Total Internal Reflection As the angle of refraction approaches 90°, something happens Instead of leaving the medium, the light is reflected back into the original medium This is called total internal reflection and is the basic idea behind fiber optic cables