A laboratory investigation uses a converging lens of unknown focal length
PHYSICS · Multi-part · CBSE · Physics · Ray Optics and Optical Instruments · Ray Optics and Optical Instruments
Problem
A laboratory investigation uses a converging lens of unknown focal length. For each of three object positions, the student measures the object distance so and the image distance si when a sharp image forms on a screen, as shown in the table.
Trial
so (cm)
si (cm)
1
25.0
75.0
2
30.0
60.0
3
35.0
52.5
All distances follow the standard real-is-positive sign convention.
(a) Determine the focal length of the lens for each trial.
(b) Calculate the average focal length from the three trials.
(c) The laboratory manual lists the accepted focal length as 20.0cm. Compute the percent difference between the experimental average from part (b) and the accepted value.
(d) The instructor considers a measurement acceptable when the percent difference is less than 5%. Based on your result in part (c), state whether the student’s measurement is acceptable and briefly justify.