Featured in PASCO’s Advanced Physics Teacher Guide

Advanced Physics Teacher Guide


This manual features over 30 College Board curriculum and AP Physics exam inspired lab activities.

Focal Length of a Lens

Lab Summary

Use a basic optics kit to determine the unknown focal length of a converging lens (spherical).


Given a converging lens (spherical) with unknown focal length, experimentally determine a value for the correct focal length of this lens.
Design and conduct an experiment to:

  • Determine the unknown focal length of the lens using the thin lens equation.
  • Show the relationships between the focal length of a converging lens and the object and image formation distances.
  • Compare experimental values for image magnification to theoretical values.


Students gain experience conducting the following procedures:

  • Assembling the optics equipment onto the optics bench and then using the movable viewing screen to locate a focused image produced by the lens.
  • Measuring and recording both so and si for 5 different lens and light source configurations.
  • Using the vernier calipers to measure the height of the image on the viewing screen for each configuration.
  • Plotting 1/si versus1/so then use a line of best fit whose y-intercept is equal to 1/f to determine f for the lens.
  • Comparing the measured values for magnification (hi/ho) to the theoretical (–si/so).

Sensors / Equipment Used:

Basic Optics System


A group of components designed to allow students conduct various optical experiments.

Materials Used:

Stainless Steel Calipers

The Associated Bundle:

Advanced Physics Standard Sensor Bundle


This bundle contains the probeware needed to perform all 37 lab activities in the Advanced Physics lab manual.

Interface Required

This experiment may require software and an interface for data collection.