PhysicsLAB Lab
Spherical Mirror Lab

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Purpose: In this lab we will experimentally determine the focal length of a spherical mirror by measuring  the size of a moveable object, the size of its image, and the position of the object. From these values we will calculate di and plot an EXCEL graph of di vs do. From the graph we will empirically determine the focal length of the mirror.
  • four meter sticks
  • one convex mirror
  • one ring stand
  • one c-clamp
  • one burette clamp
  • one tape measure
  • one magnifying (convex) lens to assist in reading the image size in the mirror
  1. Cover 50 cm of a meter stick with white paper so that it can easily be seen and measured in the mirror. This will be your object. Do NOT tape the paper to the stick - instead wrap the paper around the stick and tape the paper to itself. This way the meter sticks can easily be returned to their original condition when the lab is over.
  2. Suspend the mirror from a ring stand so that it's front edge, the vertex of the mirror, is aligned with the leading edge of the table. This will enable you to easily measure do by measuring distances along the floor.
  3. Begin by standing approximately 3.0 meters away from the mirror. Measure your actual distance and the size of the meter stick's image in the mirror. Record them in in the following data table. Repeat this procedure for 10 trials, each time decreasing your distance by approximately 30 cm.
  1. In your data chart, calculate the magnification of each trial as M = | I / O |.
  2. Next calculate di using the formula di = - M x do
  3. Input into EXCEL your values for do and di and graph your results. Save your graph as LastnameLastnameMirror.xls in your period folder and remember that a printout of your file must be part of your lab report.

Measure and record the circumference of your ornament. 

Calculate the actual focal length of your ornament. 

According to your graph's asymptote, what is the experimental focal length of your ornament? 

Calculate the percent error in your experiment. 

Using three colored pencils, complete the ray diagram for a convex mirror on the axes given below carefully. Construct and label your image. Finally measure its height and record your answer in the blank provided.


What radius convex mirror would be needed to display a 40-cm tall image of an average 5'6" (165 cm) tall person? 

List two sources of error in your experiment and explain why you chose them as being the most critical.



After submitting your results online, you are to turn in the following papers to support your work: your data table from Step 3, your EXCEL printout, your ray diagram, and your calculations for the 40-cm tall image. Remember to also return your equipment so that the next periods can set up their experiments.

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