# PHYS320 Lab 26 Geometric Optics

Experiment 1: Drawing Ray Diagrams 5.06 14.

Questions

1. Use the lens equation to predict the image distance for each case—you will have to rearrange the equation to solve for si. Remember, f is positive for a concave mirror, negative for a convex mirror, and positive for a converging lens. Write down whether the image is real or virtual in each case.

2. Measure the distance from the lens to the image on your diagrams—do your predicted image distances match what you got using the lens equation?

3. The magnification for each case is found by taking the image height divided by the object height, or m = hi / ho . For an upright image, m is positive, and for an inverted image, m is negative. What is the magnification in each of your cases?

Experiment 2: Exploring Mirrors

Questions

1. Is your image in the convex mirror a virtual image or a real image? How do you know?

2.Did this mirror give you a good view of a lot of objects to either side of you? Where have you seen mirrors like this used, and what do you think makes them useful?

3.When you held the concave mirror close to you, was the image real or virtual? How do you know?

4.How did the magnifications compare for each mirror (i.e. how big was your image in each case)?

5.What happened to your image in the concave mirror as you moved it gradually away?

6.Based on what you observed, give an estimate for the focal length of the concave mirror.

Experiment 3: Exploring Lenses

Questions

1. Did objects appear larger or smaller looking through the concave lens? What kind of image do you see through this lens, and how do you know?

2. Did objects appear larger or smaller looking through the convex lens? What kind of image is this, and how do you know?

3.What happened when you moved the lens too far away from the object? Knowing the difference between real and virtual images, explain why this happens. (Go back to Exercise 1, and note the difference between the two convex lens diagrams you drew).

4.What kind of image did you view on the screen in Procedure 2? How do you know?

5.Explain why you need the screen to view the image in this case.

6.Is it possible to view a virtual image with a screen? Why or why not?

7.How is the orientation of the image (right-side-up or upside-down) helpful for determining the type of image? Take a look at Figure 5 for some help.

Experiment 4: Mirror Images

Questions

1. As you moved the flashlight closer to the mirror, what generally happened to the image distance?

2. What was the average focal length you measured for the mirror?

3. What would the image distance si be for an object 10 m away? (Hint: you can approximate that a very far object is “at infinity”).

4.Where would the image be located if you placed the flashlight 10 cm away? Would you be able to detect this image using the same method?

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