Section 2 review
Lenses use curved surfaces to focus light rays into an image. The focal length of a lens depends on the curvature of the surface of the lens and the index of refraction of the lens material. Converging lenses can create real or virtual images, depending on the object distance relative to the focal length of the lens. Real images occur when light rays physically meet at a point; virtual images occur when the light rays only appear to meet at a point. The thin lens formula is used to calculate object distance, image distance, or focal length when the other two quantities are known. Read the text aloud
focal length, focal point, convex lens, concave lens, real image, virtual image

1 d o + 1 d i = 1 f
m= d i d o

Review problems and questions

  1. Does a flat mirror produce real or virtual images? Read the text aloud Show
  1. Does a concave lens produce real images, virtual images, or both? Read the text aloud Show
  1. A thin convex lens produces an image that is magnified and inverted. Where is the object located? Read the text aloud Show
  1. Cassandra has a lens with a focal length of 20 cm. Where should she place an object to get an image at a distance of 60 cm? Read the text aloud Show
  1. Damien places an object at a distance of 90 cm from a lens, and the image distance is 30 cm.
    1. What is the focal length of his lens?
    2. What is the magnification? Read the text aloud Show
  1. A one-dollar bill is 6.5 cm high by 15.5 cm wide. When the bill is placed 26 cm away from a thin convex lens, an inverted image of the dollar bill is projected onto the wall 1.0 m away from the bill on the far side of the lens.
    1. Is the image real or virtual? How do you know?
    2. What is the image distance di ?
    3. What are the dimensions of the image? Read the text aloud Show
  1. A simple projector shines light through a slide to project an enlarged image of the slide on the wall. Slides with a width of 6 cm are placed 11 cm, behind a lens with a focal length of 10 cm.
    1. Where does the image appear? How far should the projector be from the wall?
    2. What is the magnification?
    3. How large is the image?
    4. What does the orientation of the image mean? Read the text aloud Show

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