Activity 1: Converging Lens

Lens Optics

Activity 1: Converging lens

1. Write down the lens equation from Chapter 23:

1. Set up the track at your table with light source in the middle. Put the screen at the other end, and put the converging lens in between. Adjust the light source and screen positions until you get a clear image on the screen. Is this image real or virtual? Is it upright or inverted?

1. Move the light source a few centimeters closer to the lens. The image should now be blurry. Move the screen to find the new image location. Was it where you predicted?

1. Move the screen and light source so they are about 115 cm apart, as in the figure below.

1. Move the lens to create a clear image on the screen. Record the object and image distances and the object and image sizes in the table on the next page.

1. Move the screen closer to the light source and repeat #5.

1. Use the lens equation from #1 to find the focal length of the lens. Do this for both data sets, verify that they are both similar to the value written on the lens.

1. Verify that the ratio of image to object distance is the same as the ratio of image to object height (this value is the magnification).

1. Another way to find the focal length is to find the image distance for an object at infinite distance from the lens (). Position your screen so it is facing a window in your classroom. Place the lens in front of the screen and move it until you produce an image on the screen and measure the image distance. Use the equation in #1 to calculate the focal length of the lens.

Experiment 2: Diverging lens

1. Set up your light source, screen, and diverging lens. The lens should be about 20 cm from the light source. Move the screen until you create a clear image. Does this work? If not, why not?

1. Remove the screen and instead try to look through the lens to see an image. Does this work? Is this image real or virtual? Is it upright or inverted?

1. Have one person in your group (The Looker) look through the lens to see the image. Have another person in your group (The Finder) hold a ruler next to the track. Have the Finder move the ruler back and forth until the Looker sees the ruler at the same distance as the image. Record the image distance.

1. Use the lens equation, the object distance, and the image distance to calculate the focal length of the diverging lens. Does this match the written value?

Experiment #3: Both lenses

1. Place the light source at one end of the track, and the converging lens 30 cm away. Calculate the image distance you expect from this setup, using the focal lengths you found in the first two experiments.

1. Place the screen at your calculated location. Did it work?

1. Remove the screen and place the diverging lens 10 cm away from the light source. Calculate the image distance and image height you expect from this multi-lens setup.

1. Place the screen at your calculated location. Did it work?

1. Does it make sense that the new image distance is greater than before?

1. Create a focused image on the screen with just the converging lens. Take a piece of paper and block the top half of the lens. What happens to the image? Is it what you predicted?

1. Draw a ray diagram of your current experimental setup, including the light blocker. Does your ray diagram show why you got the correct results? Check your diagram with Dr. Mitchell.