Peer Review

Spherical Lenses & Mirrors

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Overall Rating:

Content Quality:

Effectiveness:

Ease of Use:

Overview:: This applet demonstrates via ray tracing the formation of real and virtual images of both Concave and Convex Mirrors and Lenses. The user can change the object distance or object height, or the focal length, and observe the resulting image. Several light rays are automatically drawn for the user.
Type of Material:: Java simulation in a browser window.
Recommended Uses:: Preclass or inclass demonstrations, reinforcement of material discussed in class by the Instructor, and homework exercises.
Technical Requirements:: A web browser that supports Java.
Identify Major Learning Goals:: To help gain both a qualitative and quantitative understanding of how images are formed by both convex and concave mirrors and lenses. To help with applying the lens and magnification equations to various situations along with sketching in the light rays that form the images. To understand how reflection and refraction by curved surfaces leads to image formation.
Target Student Population:: High school and lower division undergraduate.
Prerequisite Knowledge or Skills:: Basic knowledge of geometric optics and the three principle rays and the lens and magnification equations.

Rating:
Strengths:: The content is excellent. The applet provides both qualitative and quantitative results for each of the standard situations. Focal length and object position and height are all adjustable. The magnification and lens equations support the results on the screen. The formation of the light rays is accurate.
Concerns:: None noted.

Rating:
Strengths:: The ability for students to drag the object is a highly effective method for showing how image position is affected by the object's position in relation to the focal point. The position of the lens (or mirror) can also be changed; this allows for a wider variety of cases to be examined.

This applet provides an excellent method for illustrating how both real and virtual images are formed. This can be a little difficult in a class room environment. This can be an excellent supplement to a paper and pencil exercise where students draw in light rays themselves. The students can essentially check their work. The problems from a textbook are mostly quantitative whereby the student uses the lens equation exclusively. This applet will help with drawing the principle and various other light rays. Instructors should point at that the applet shows the standard key rays (e.g parallel to the principle axis and through a focal point) by double clicking.
Concerns:: Because this is a stand-alone applet, the instructor will need to integrate this resource into the class activities.

Rating:
Strengths:: The author provides a few instructions but the simulation is selfexplanatory for the most part. There are only three (3) controls that can be changed by dragging the mouse.

The java applet downloads very quickly.

The light rays are coloredcoded to distinguish between real and extended rays. The image distance and height update automatically at the bottom of the screen when the user makes a change. Furthermore, the light rays update in realtime.
Concerns:: Although focal length is adjustable, the default value is the minimum allowable. This might lead some users to conclude that focal length isn't adjustable, since it will only change if the focal point is dragged in one direction. The user can only change the object distance and object height by clicking and dragging the object. The user can not make any changes by typing in numbers.

Other Issues and Comments:: This is one applet in a collection of several dozen similar resources developed by the author. These all are focused simulations that consider a single physical situation.
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