32: Images
- Page ID
- 166341
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Stand in front of a bathroom mirror and raise your right hand. The figure facing you raises its left. Read the word ambulance stenciled in reverse across the front of an emergency van and your mirror untangles it instantly. Yet here is a puzzle that has bothered thoughtful people since antiquity: a mirror flips left and right, but it does not flip up and down. Your reflection’s head stays up and its feet stay down. Why should a flat sheet of glass care about the difference between horizontal and vertical? The mirror, of course, does nothing of the kind, and by the end of this chapter you will be able to say exactly what it does instead.
Answering that question is really the business of this whole chapter: understanding images, where light decides to reassemble a picture of an object after bouncing off a mirror or passing through a lens. The same handful of ideas that explain your reflection also explain how a telescope gathers a galaxy, how a camera freezes a face, how your own eye throws the world upside down onto your retina, and how a magnifying glass enlarges the fine print. We will build the toolkit one optic at a time (flat mirrors, then curved ones, then lenses, then whole systems of them) and we will return at the end to the mirror that started it all.
Learning Objectives
- Distinguish real from virtual images and explain how each is formed.
- Locate and describe the image in a plane mirror, and explain the left–right “reversal.”
- Apply the mirror equation and magnification to concave and convex spherical mirrors, using a consistent sign convention.
- Trace principal rays to locate images for mirrors and lenses.
- Apply the thin-lens equation to converging and diverging lenses, and use the lensmaker’s equation to relate focal length to a lens’s shape.
- Analyze multi-element optical systems by treating each image as the object for the next optic.
- Explain how the eye focuses, correct near- and farsightedness with lenses of the right power, and find the magnification of a magnifier, a microscope, and a telescope.
We will return to the left–right puzzle of the plane mirror in the final problems.