$11\mathrm{.}2$

Introduction

This week, you will use lenses and light sources to explore some basic principles of geometric optics. In the end, you will determine the index of refraction of an unknown transparent material.

$11\mathrm{.}3$ Apparatus

A sketch of the apparatus is provided in Fig. $11\mathrm{.}1.$ A light source, lens, and screen are fixed to optical carriages. The carriages run along a cast$-$iron optics track. Positions along the track are marked on the side. Three different convex lenses and a Vernier caliper have also been provided.

EQUIPMENT NOTES

The lenses and screens are glass. Please handle the lenses and screens with care and be gentle when moving the optical carriages. The optical carriages may stick on the optical rail, causing the lens or screen to tip. Please hold the carriage firmly when moving it$,$ so that the lens or screen remains upright.

$11\mathrm{.}4$ Theory

Convex lenses can bend light from a source such that the light forms an image of the source at a particular point in space. The distance between the object and the lens is called the object distance, o$.$ The distance between the lens and the image is called the image distance, $i.$ The lens equation is a mathematical model which relates the object distance to the image distance through a quantity called the focal length, $f.$ The lens equation is

$\frac{1}{o}+\frac{1}{i}=\frac{1}{f}$