Trick to drawing ray diagrams for converging lens:
- There is one ray of light passing through the center of the lens. Always.
- 2 rays are enough to determine the position of image/object.
- The other ray of light ALWAYS passes through the focal point of the lens. Either the first focal point of the second focal point.
- If a ray passes through the focal point before passing through the lens, the refracted ray will be travelling parallel to principal axis.
- If a ray is parallel to principal axis before passing through the lens, the refracted ray will pass through the focal point.
- Use solid lines for real light rays and put arrowheads to indicate direction
- Use dotted lines for extended light rays (virtual light rays) and do not add arrowhead
- Use solid lines for real images and dotted lines for virtual images
You can check the tricks above with the diagrams below. (Click to zoom)
- An image that is real is always inverted!
- An image that is virtual is always upright!