Tutorial details

The first section of the tutorial develops the method of parallax. It begins with a brief experiment to illustrate the need for such a method. In the next part of the tutorial, students use parallax to determine the location of the image of a nail in a plane mirror. Even students who have previously heard that the image is behind the mirror are often surprised to see that a second nail placed at the image location appears to overlap the image independent of viewer location.

The following part of the tutorial develops ray tracing as a technique to determine image location. Students first recognize that only two lines of sight are required to determine the location of a (point) object. They then apply this idea to determine the location of the image of a nail in a plane mirror. Using lines of sight that they have drawn, they complete the diagram to show the entire path of light from the object to an observer’s eyes. This part of the tutorial also helps students to interpret the image location as the point where the nail appears to be located, that is, the image location tells where to look to see the image.

In the final section of the tutorial, students are guided in using ray tracing to determine the location of a point object in a plane mirror. Two conventions are introduced: a solid line with an arrow head to represent a ray, and a dashed line to extend a ray so that it shows the direction from which the ray appears to have come.

For instruction tips, login or register as a verified educator to see the Instructor Guide.

Prerequisite tutorials

The Light and shadow tutorial is a prerequisite to Plane mirrors.

Other prerequisites

It is be helpful for students to have worked through the tutorial Light and shadow. It is expected that students know the law of reflection.

Equipment

List

• mirror supports
• protractor
• straight edge
• white board or large sheet of paper with markers
• plane mirrors ~5 cm × 7 cm

Discussion