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Convex Lenses and Magnification

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Geometrical optics: Focal points, principal rays, drawing and interpreting ray diagrams, lateral and angular magnification

Points of Emphasis

Part I: Use of focal points and principal rays in drawing and interpreting ray diagrams. Part II: interpretation of ray diagrams in the context of lateral and angular magnification.


This lab provides an introduction to geometrical optics and is divided into six sections.

Section I - Convex lenses. Students determine the location of the image of a distant object that lies on the principal axis of a convex lense. Considering the reversibilit of the path of the light, they are led to developtwo rules for principal rays: (1) a ray that arrives at a lens parallel to the principal axis passes through the focal point on the other side of the lense. (2) A ray that passes through the focal point emerges parallell to the principal axis.

Section II - Ray Tracing and Convex Lenses. Students determine the paths of all rays that leave a given point on an object and pass through the lens. They are led to the concept that a third principal ray that passes through the center of the lenses is undeflected.

Section III - Magnification - Apparent Size. Students view objects from different locations and determine that the apparent size and width of the object depends on it actual size and on its distance from the observer.

Section IV - The Image of an Extended Object. Students are given practice in relating ray diagrams to what and observer sees in a lens.

Section V - A Magnifying Glass. Students apply what they learned in section IV to a magnifying glass.

Section IV - Magnification. Students are introducted to the concepts of lateral and angular magnification and learn to distinguish between the two types of magnification.

Course Level

Introductory level courses: Physics 4 and Physics 14

Student Handouts

Faculty may see either David Abbott or Jan Largent for a copy of the write-up and the lab homework.


Number of set-ups available: 10

Per lab station:

1 optical bench
4 optical bench mounts
3 lense holders
1 object lamp
1 lense set
1 flashlight
2 coke cans
1 D-Cell
1 ruler

Convex lenses and magnification lab apparatus


  1. This lab exercise comes from Tutorials in Introductory Physics by Lillian C. McDermott, Peter S. Shaffer and the Physics Education Group, Department of Physics, University of Washington. It is a combination of the tutorials: Convex Lenses and Magnification.

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Site contact:largent@Dartmouth.EDU

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