# Lens equation discussed

1. An overhead projector with a lens of 35.6-cm focal length is used to throw an image on a screen 1.80 m away. If you consider the lens to be a thin lens, how far is the slide from the lens when the image is in focus? What is the magnification in this setup? Work this problem by ray tracing?

2. Work Problem 1 using the thin-lens equation?

3. An incandescent light bulb is marked "60 W" on its upper end. A lens of 25-cm focal length, when held above the light bulb, forms an image of the "60 W" on the ceiling. If the distance from the lens to the ceiling is 1.30m, how much larger are the letters and numbers in the image on the ceiling than on the object light bulb? Work this problem by ray tracing.

4. A luminous object is placed 3.00 m from a screen. When a lens is interposed between the object and the screen at a distance of 0.50 m from the screen, an in-focus image of the object forms on the screen. It is claimed that if the object is moved 1.70 m farther from the screen and the lens moved 0.30 farther from the screen, the image will again be in focus. Is this claim true?

5. Two thin lenses, each with + 12-cm focal length, are placed 60 cm apart. An object 18cm to the left of the first lens is imaged a distance of x to the right of the second lens. Determine x?

6. A 3.0-cm-tall domino is located 100cm from a concave spherical mirror of R = 30cm. Locate the position of the image and find the magnification?

7. A shiny, spherical Christmas tree ornament is 95 mm in diameter. (a) Where is the image of a child standing 2.0 m away from the ornament? (b) What is the magnification of the image? (c) Is the image inverted or erect?

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