Refraction is the bending of light as it travels from one medium to another. Medium: material through which electromagnetic waves (e.g. Light) propagate. Occurs at the boundary of the 2 materials Light travels in a straight line and at a constant speed as long as the medium it is travelling through is the same. As light travels from one medium to the next, its speed and direction changes. This causes light rays to refract (bend).

Refraction vs Reflection What is the difference? Refraction is the bending of light rays when it travels from one medium to another and changes its speed. Reflection is when light rays bounce of a surface rather than passing through.

Normal Incident ray Air Water Refracted ray Angle of incidence (θi) Angle of refraction (θR) Refracted ray

Fermat’s Principle When light travels from one point to another, it follows the path that will take the least time. In one medium, this is a straight line. Light bends when changing mediums so that it travels for a greater distance in the faster medium.

Laws of Refractions (Snell’s Law) When light rays travel from a less dense medium (where its speed is faster) into a MORE dense medium (where its speed is slower), the refracted ray bends TOWARDS the normal. When a light ray travels from a more dense medium (where its speed is slower) into a LESS dense medium (where its speed is faster), the refracted ray bends AWAY from the normal.

Understanding the Mechanics of Refraction B) A) FST = Fast to Slow, Towards Normal B) SFA = Slow to Fast, Away from Normal

Index of Refraction Formula Where: n = index of refraction (no units) (indicates how much the incident ray was “bent” in becoming the refracted ray) c = speed of light in a vacuum [3.0 x 108 m/s] v = speed of light in another medium [in m/s].

Index of refraction The index of refraction for light in a vacuum is 1.00 (exactly). All other media have larger values. The larger the value of its index of refraction, n, the slower light travels in the medium and the more dense the medium is. For example, n = 1.0003 in air and n = 1.33 in water so light will travel more slowly in water than in air. Water is more dense (1.0 g/cm3) than air (0.0013 g/cm3). Note: Table containing Index of refraction provided in your textbook (p. 437). This information will be provided to you on the quizzes, test and final exam.

Snell’s Law θ1 = angle of incidence in the less dense medium (e.g. air) θ2 = angle of refraction in the more dense medium (e.g. plastic, water) n = index of refraction A general equation for light travelling directly from Medium 1 with an index of refraction n1, to Medium 2 with an index of refraction n2, can be written as: Speed of light in a vacuum Speed of light in the medium

Snell’s Law Practice Problems Determine the index of refraction when the angle of incidence in air is 45° and the refracted angle in the more dense medium is 33°. When light passes from water into diamond at an angle of 45° from the normal, what is the angle of refraction?