Post-Lab Activity

(Place the answers to the following four questions in your course notebook - on the left side.  Label your work as Physlet - Adjustable Angle Mirrors.)

This animation shows two plane mirrors which are at an angle to one another. The angle between the mirrors can be adjusted by dragging the green dot on the tip of the top mirror.  The angle can be adjusted between 20 degrees and 180 degrees.  The blue line with the orange-red dot at its extremity is the object. Other blue lines with yellow dots at their extremity are images.  The size and orientation of the object can be adjusted by dragging the orange-red dot about the screen.

1.  Experiment with the applet by adjusting the angle between the mirrors to 180º, 120º, 90º, 72º, 60º, 45º, 40º, 36º, and 20º.  For each angle, determine the number of images observed.

2.  The angle values provided above were not randomly selected.  They were strategically chosen for a specific reason.  Carefully compare the number of observed images for the given angles to the number of images observed for and angle which is 2-3 degrees lower or higher.  Describe the difference in the number  of images and describe what happens at the strategically chosen angles of question #1.

3. How do your measurements in this lab compare to the measurements made in Lab RM6 - Improving Your Image?  Do you need to return to lab to check any measurements?  If so, then you should consider doing so soon.

4.  Do you see any pattern in the data collected from question 1?  To assist in seeing the pattern,  drag the top mirror to slowly adjust the angle from 180º to 20º.  Pay attention to the light yellow and light grey lines and to the mirror extension lines.  Express the numerical relationship relating the angle between mirrors and the number of images using words and/or an equation.

More information on dual mirror systems can be fount at The Physics Classroom Tutorial.

Idea for this question was generated by Illustration 33.2, authored by Anne J. Cox for the Physlet Physics book.

Applet authored by Fu-Kwun Hwang.

Special Thanks to Wolfgang Christian and Mario Belloni of Davidson College for placing applets in the public domain.

More applets and information about using them is available at the Davidson College website: