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Refraction, properties of lenses, defects in human eye.
INTRODUCTION
This experiment is conducted in two parts. The aim of part one is to determine the density of an unknown material through measurement of its refractive index and by measurement of its mass and volume. The aim of part two is to determine the focal length of planar convex, biconvex and biconcave lenses made from the same material.
Key vocabulary in this experiment includes:
Density Refractive index Snell’s Law medium
Image myopia Optical axis Focal length
Planar convex Biconvex Biconcave
THEORY
Refractive index
The refractive index of a material describes the propagation of light through the material. In this investigation it will be determined using Snell’s law in which light travelling through medium 
is incident at angle 
to the normal and is refracted in medium 
at angle 
to the normal.
To determine the refractive index of a medium using Snell’s law the angle of incidence maybe adjusted and the angle of refraction measured so that, for air ( =1.00)
A graph may therefore be plotted to find the refractive index of the second medium from the gradient.
The refractive index is related to material density as follows: n=4.545D-3.602
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| FOCUS 11 POSITION OF ADVERBS | | | Part 2: Determination of focal length. |