# Chapter 2: BASIC OPTICAL PRINCIPLES

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1. Electromagnetic energy travels at the speed of light
(approx. 2.9x10^8 m/s or 186,000 miles/sec) in the form of a wave.
2. Wavelength
distance between two corresponding points on two consecutive waves
3. Electromagnetic wavelengths
range in scale from that of an atomic nucleus (gamma rays) to that of a small planet (radio waves).
4. visible spectrum
lie between 400 and 700nm,with red light at the longer end of the spectrum and violet light at the shorter end.
5. ultraviolet
visible spectrum from 1 to 400nm lies
6. infrared
just above from 750nm to 1mm
7. index of refraction
• is a measure of how much the speed of light is altered as enters a given media relative to the speed of light in air.
• n = speed of light in air / speed of light in selected material
8. Lens power
• Power = 1 / Focal Distance
•      EX:Power = 1 / Focal Distance
•           Power = 1 / 0.50 m
•           Power = 2.00 D
9. Prism
can be used to correct vision for an individual whose eyes are not perfectly aligned as with, for example, a patient with strabismus
10. prescriber's method
specifies the direction if the prism in terms of the base, using base-up, base-down, base-in, and base-out (base-in referring to the direction of the nose and base-out referring to the direction of the temple)
11. Prentice's Rule
Prism= hcm xD
12. plus lens
likened to two prisms base-to-base, as the lens is thicker in the middle and thinner at the edges.
13. minus lens
two prisms apex-to-apex, thinner in the middle and thicker at the edges.
14. prism by decentration
the lens power is sufficient, to induce the prescribed prism, the lens can simply be cut off-center to achieve the required results

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 Author: Anonymous ID: 244727 Filename: Chapter 2: BASIC OPTICAL PRINCIPLES Updated: 2013-11-03 20:00:08 Tags: Folders: Description: optical Show Answers:

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