Images and Ray Diagrams

• Real image


  Light from an object comes together to form an image on a 'screen' like the image formed on an eye's retina
• Virtual image


  Rays are diverging, so the light from the object appears to be coming from a completely different place
• Virtual image


  • When you look in a mirror, you see a virtual image of your face
• Virtual image


  • When looking at an object through a magnifying lens, the virtual image looks bigger than the object actually is
• Describing an image


  • How big it is compared to the object
  • Whether it's upright or inverted (upside down) relative to the object
  • Whether it's real or virtual
• Draw a ray diagram for an image through a convex lens


  1. Pick a point on the top of the object, draw a ray going from the object to the lens parallel to the axis of the lens

  2. Draw another ray from the top of the object going right through the middle of the lens

  3. The incident ray that's parallel to the axis is refracted through the principal focus (F) on the other side of the lens, draw a refracted ray passing through the principal focus

  4. The ray passing through the middle of the lens doesn't bend

  5. Mark where the rays meet, that's the top of the image

  6. Repeat the process for a point on the bottom of the object
• Object at 2E


  Produces a real, inverted image the same size as the object, and at 2E
• Object between F and 2E

  Makes a real, inverted image bigger than the object, and beyond 2E
• Object nearer than E

  Makes a virtual image that is upright, bigger than the object and on the same side of the lens