Lab & Pre-lab #11

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Lab Partners:
Date:
Lenses and Images
Objectives
• To understand what is meant by the focal point of a lens.
• To understand the relationship between the object distance, the image distance and the
focal length of a lens.
• To understand the types of images formed by a lens.
Overview
Lenses are used in many devices that we use everyday-they are essential for the operation of
cameras and projectors. Lenses are needed for devices such as microscopes to magnify small
objects so that we can see them.
In the previous lab you studied the refraction of light rays by lenses. In this experiment we
will continue this investigation by observing images formed by lenses in various arrangements,
and determining how the positions and sizes of these images are related to the positions and
sizes of the object.
These labs have been adapted from the Real Time Physics Active Learning Laboratories [1].
The goals, guiding principles and procedures of these labs closely parallel the implementations
found in the work of those authors [1, 2, 3].
Investigation 1:
Images formed by a convex lens
Every lens has two focal points. The importance of these points is that all light rays reaching
the lens coming from a very distant object (ideally, infinitely far away) will be focused at a
focal point, as in Fig. 1.
The focal length is the distance from the center of the lens to a focal point. The focal length
depends on how the lens is made. The curvature of the surfaces of the lens determines the focal
length.
Prediction 1.1 Will a lens whose surfaces have very little curvature have a smaller or larger
focal length than one for which the surfaces have greater curvature
To carry out this activity, you will need the following:
• One 15 cm focal length convex lens.
• One 30 cm focal length convex lens.
• optical bench.
PHYS-204: Physics II Laboratory 1