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Unformatted text preview: tion to Snell’s Law. So what happens if you increase θi beyond that point? All of the light is
reﬂected and none is refracted, a condition referred to as total internal reﬂection. It is called this because
all of the light is reﬂected back into the dense media.
sin θcritical = 2.5 nr
ni (4) The Lens Maker’s Equation The focal length of a simple lens depends on the radii of curvature of the lens’ two surfaces and the
difference in the index of refraction between the lens and the surrounding media. Speciﬁcally, this can be
represented by the Lens Maker’s Equation:
= nl − nm
R1 R2 (5) where R1 is the ﬁrst surface and is positive if it is convex, R2 is the second surface and is negative if it is
convex (and conversely). The quantity nm is the index of refraction of the surrounding media and nl is that
of the lens material. In air, nm ≈ 1. If you have a lens with one ﬂat side, it is the equivalent of that side
having R = ∞, or R = 0. If this is confusing, ask your instructor why! 3 Equipment
• laser pan apparatus
• green laser
• polished acrylic-plastic block; plano-convex, plano-concave, bi-convex, and bi-concave acrylicplastic lenses
• 60◦ acrylic-plastic prism
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This document was uploaded on 02/15/2014.
- Spring '14