Archibald/Hall CLASS SET—PLEASE DO NOT REMOVE

2/23-24/11

Intro to Optics and Lenses Lab

Objectives:

  1. Observe and explain how images are projected through a pinhole
  2. Describe the ray model of light and draw ray diagrams for images
  3. Connect concepts of projection and refraction to understand lens optics
  4. Solve for the focal length of a biconvex lens and draw ray diagrams for an image shown through a biconvex lens

***READ ALL INSTRUCTIONS and DIAGRAMS CAREFULLY!!!!***

Part 1: Images Projected through Pinhole

1. Set up a data table on your own paper with FOUR headings: Description of Light Source, Aperture Size, Prediction for Image, Description of Projected Image.

2. Before each trial you must write down a prediction in your data table for what you will see on the viewing screen

3. Shine each of three light sources (1 point, 3 point, and line) through each of two apertures (pinhole and 1cm hole) on to the viewing screen. This will be a total of 6 different set ups for your data table.

Questions for Part 1:

1. Take notes on Ray Diagrams. Show your notes and the sample ray diagram here. Why do we only use the three “principal” rays?

2. How does the size of the aperture affect the brightness and clarity of the projected images. Explain why you think this is the case?

3. Draw a ray diagram showing why the 3 light sources projected upside down and backwards.

Part 2: The Focal Length of a Lens

1. Use the light boxes to shine the 5 lines of light at the prism. You should see exactly the same thing as last time, but with five lines instead of one. Draw the incident light, and the refracted light coming out of the prism. Then add in the normal lines and the refracted light in the prism

**Remember that the angle of refraction is toward the normal line, which is perpendicular to the surface of the prism**

2. Draw the shape of the lens on your paper. Now, draw 4 or 5 different normal lines on the right side of the lens. How are these normal lines different from the rectangular prism?

3. Shine the five lines of light at the lens. Draw what you see. How do these lines act compared to the normal lines of the lens? Draw the normal lines on your picture.

4. Find the point where all the refracted beams converge (come together) this point is called the focal point. Measure the distance from the lens to the focal point. This is called the focal length. The focal length differs from lens to lens depending on what it’s made of (it’s index of refraction) and how curved its surface is. The focal length exists on both sides of the lens

5. Obtain a magnifying glass and find the focal point. Turn the light box on its side and shine the 5 rays through the magnifying glass on to a screen. Measure and record your focal point, then give TWO reasons why this focal length differs from the other lens.

Part 3: Images formed from Lenses

1. Make a data table very similar to Part 1. This time you’ll just use the 3 point light and the tall bulb, and instead of two aperture sizes you’ll have 3 “object positions”: behind f, at f, with in f (f=focal length)

2. Do all of the set ups (6 again), making predictions first, to complete the data table. The viewing screen should always be placed beyond the focal point.

Questions for Part 3:

1. Take notes on ray diagrams for lenses here. Include sample ray diagram.

2. Explain the connection between the size of the image and clarity. How does this relate to where the image screen is in relation to the focal distance.

3. Set up the 3 light source, set a position out side the focal length, and use the 3 principal rays to draw a ray diagram of the projected image