# Week 33 (Apr. 7 - 11)

**Reading:**Geometric optics (Chap. 36)

**images formed by flat mirrors, spherical mirrors, lenses, the thin lens equation, the human eye, telescopes**

Key Topics:

Key Topics:

**Homework Problems:**

**Converging lens problem:**A 4 meter tall tree is located 5 meters in front of a converging lens of focal length 5 cm. Where is the image formed? Is the image real or virtual? Upright or inverted? What is the magnification of the image? What is the height of the image?*Answer: image distance: 5.05 cm. Real image. Inverted image. Magnification: -0.0101. Image height: 0.0404 meters.***Diverging lens problem:**What if the tree is located 5 meters in front of a diverging lens with focal length -5 cm? Answer the same questions.*Answer: image distance: -5.05 cm. Upright image. Magnification: 0.0101. Image height: 0.0404.***Magnifying glass problem****:**A magnifying glass has a focal length of 4 cm. A 1 cm long bug is located placed 2 cm from the magnifying glass. Where is the image formed? Is it real or virtual? Upright or inverted? what is the magnification?**Keplerian telescope problem****:**A Keplerian telescope has the following specifications: The focal length of the objective lens is 1000 mm. The focal length of the eyepiece is 5 mm. What is the magnification of the telescope (technically, this is called the angular magnification)? What is the approximate length of the telescope?*We did not discuss how to compute the mangification of a keplerian telescope in class, but I've posted the answer anyhow.***Nearsightedness problem****:**What type of eyeglasses should a nearsighted person wear? (e.g. diverging, converging?)**Solid angle problem****:**An American Eagle 1 ounce gold coin is held at arm's length. What is the solid angle occupied by the gold coin? How far must you hold it from your face so that it perfectly covers the moon? (Hint: you will need to look up some information about the moon.)**Counting the stars****:**A sailor standing on the deck of his boat in the middle of the south pacific ocean gazes through a 30 cm long 3 cm diameter hollow tube. He is able to count 20 visible stars through the tube. About how many stars are above the horizon? How did you estimate this number?