PH - 262 / 11 Fall 2001

Engineering Physics II

Professor: Alvandi

Submitted By:

Andrew Buettner

Partner: Peter Fetterer

Lab #7: Image Formation by a Thin Lens

Thursday, March 06, 2003

Table Of Contents

1) Cover Page...............................1

2) Table of Contents.....................2

3) Objective..................................3

4) Components Used....................3

5) Procedures................................3

6) Lab Data / Results.....................3



1) Table 1...........................................3

2) Table 2...........................................4

3) Table 3...........................................4

4) Table 4...........................................4

5) Table 5...........................................4

7) Answers to Lab Questions.........7

8) Conclusions...............................8

9) Attachments...............................8

Objective

The objective of this lab is to investigate the properties of a thin lens by observing the images that it forms.

Components Used

1) Optical bench

Procedures

I) Part 1: Determining the Focal Length

1) Place the light source at one end of the table bench.

2) Place the screen at the other.

3) Place the lens near the center.

4) Move the arrow hole between the light and the lens until a clear image is seen on the front screen.

5) Measure the distance between the lens and the screen (q).

6) Measure the distance between the arrow and the lens (p).

7) Repeat steps 3 - 6 using two other locations for the lens. ** Book says "object"... assuming lens **

8) Remove the light source, and screen.

9) Shine a bright light (sunlight) through the system.

10) Move the arrow hole until a clear image is projected on a nearby wall. ** Book says "screen"... No screen exists, removed in step 8, assuming wall.

11) Record the "p," and "q" values.

II) Part 2: Chromatic Aberration

1) Cover the light with a color filter.

2) Perform steps 1:1 - 1:7

3) Repeat steps 1 - 2 using two other colors.

Lab Data / Results

1) Table 1: Transparent Object Results

Trial #:	1	2	3
(p) Value:	21.4cm	20.5cm	19.5cm
(q) Value	50cm	60cm	70cm

2) Table 2: Red Object Results

Trial #:	1	2	3
(p) Value:	21.5cm	20.7cm	20.0cm
(q) Value	50cm	60cm	70cm

3) Table 3: Green Object Results

Trial #:	1	2	3
(p) Value:	21.4cm	20.4cm	19.6cm
(q) Value	50cm	60cm	70cm

4) Table 4: Blue Object Results

Trial #:	1	2	3
(p) Value:	21.3cm	20.1cm	18.9cm
(q) Value	50cm	60cm	70cm

5) Table 5: Infinite Distance Data

Distance Between Lens and Screen:	15.1cm

Answers to Lab Questions

1) Q: Explain why the focal length is equal to the image distance if the object distance is large, and what object distance would produce a .5% discrepancy between (f) and (i) if f=20cm?

A: 1/f = 1/p +1/i, if p approaches infinity, f becomes equal to i. P = 100M

2) Q: Show 3 diverging lenses.

A:

3) Q: Show the apparatus used to perform this experiment.

A:







4) Q: Give the formula to compute the focal length, how does it relate to this experiment?

A: 1/f = 1/p + 1/i. The focal length can be directly calculated using the values obtained in this experiment.

5) Q: What is chromatic aberration, and how did it affect the results, an why does it help to use a thin rather than thick lens?

A: Chromatic aberration is the augmented focal length caused by wavelength, it caused certain wavelengths to have a longer or shorter focal length, the thinner the lens, the less effect this has on the results.

6) Q: In what ways is a reflecting telescope better than a refracting one?

A: A reflecting telescope can achieve a greater magnification for it's size, it does not invert the image, it allows more light to enter it, and is less subject to wavelength distortions.

7) Q: Compute the focal length for each trial, and calculate the average value.

A: f₁ = 14.99cm; f₂ = 15.28cm; f₃ = 15.25cm; f_avg = 15.17cm

8) Q: Using f_avg from Q₇, compute the error for the focal length obtained in the Infinite Distance data.

A: %error = .984%

9) Q: What is the average focal length for each color, and explain results. Are the values expected?

A: f_Red = 15.24cm; f_Green = 15.17cm; f_Blue = 14.96cm

10) Q: What is the curvature of the lens?

A: Unable to calculate: No n value Given!

Conclusions

This lab has demonstrated the refractive properties of a thin lens. The error for this lab was relatively low (<1%). Unfortunately this lab was plagued with typos and missing information. I performed that lab as best as I could with the components and procedures given, and was mostly successful. The original lab must be re-written before any one else attempts this lab.

Attachments

1. Original lab data

2. Calculations