Lenses & Mirrors: Where Light Goes

Mirrors: Light That Bounces

Mirrors create images by reflecting light in predictable ways.

• Flat (plane) mirrors: These make virtual images (which appear behind the mirror) the same size as the object, but with the left and right sides swapped.
• Concave mirrors (curved inward): 
  • Close to the mirror: image looks bigger and upright (makeup/shaving mirrors).
  • Farther away: The image is real and inverted (used to focus light on flashlights and telescopes).
• Convex mirrors (curved outward): Give a wider view but make images smaller, which is why car mirrors warn “closer than they appear.”
• The inside of a spoon acts like a concave mirror; the outside acts like a convex mirror.

Lenses: Light That Bends

Lenses make images by refracting light—bending it as it passes from air into glass and back out.

• Convex (converging) lenses: Bend light together toward a focal point.
  • Object closer than the focal length: image is virtual, upright, and magnified (how a magnifying glass works).
  • Object far away: image is real and inverted (used in cameras and your eye).
• Concave (diverging) lenses: Spread light apart, making images virtual and smaller (they are used in nearsighted glasses).
• Magnifying glasses use a convex lens to make a larger virtual image.

Fun Facts

Here are some interesting facts about lenses and mirrors:

• Bike and road reflectors use corner-cube mirrors to send headlights straight back to drivers, making signs and reflectors appear to glow.
• Phone cameras use lenses to focus a real, initially upside-down image onto a screen, and the device then flips it upright.
• Anti-glare glasses use ultra-thin coatings that cancel reflections, so the lenses often show a faint purple or green tint.
• A Fresnel lens is a thin, ring-shaped lens that focuses like a thick one. Because of its lighter weight, it’s used in lighthouses.

Review

Let’s quickly recap what we learned about lenses and mirrors:

• Which lens brings parallel rays together? Convex Lens
• Which mirror gives a wider view but smaller images? Convex Mirror
• Which type of lens spreads light rays apart? Concave Lens
• Which vision problem is corrected with a concave lens? Nearsightedness