What is the Ray Optics Lab?
Quick Answer: An interactive simulation of lenses and mirrors. Choose convex/concave lens or mirror, adjust focal length, object distance, and height. See real-time ray diagrams, image formation, and compute image distance, magnification, and nature (real/virtual, upright/inverted).
Theory of Geometric Optics
For thin lenses and spherical mirrors, the lens/mirror equation relates object distance u, image distance v, and focal length f:
1/v + 1/u = 1/f (lens, real-is-positive sign convention) or 1/v + 1/u = 1/f with sign conventions depending on element.
Magnification m = -v/u (height ratio). The sign of v and m determines if the image is real/virtual and upright/inverted. The simulator uses the Cartesian sign convention: light travels left to right, object distance positive if object is on incoming side, focal length positive for convex lens and concave mirror. Ray tracing uses principal rays.
Step-by-Step Examples
Example 1: Real Image with Convex Lens
- Select "Convex Lens", f = 120 px. Place object at u = 240 px (beyond 2F).
- The image forms between F and 2F on the other side, real, inverted, diminished.
- Reduce u to between F and 2F: image moves beyond 2F, enlarged, still inverted.
Example 2: Virtual Image with Concave Lens
- Choose "Concave Lens", f = -120 px. Any positive object distance yields a virtual, upright, diminished image on the same side as object.
Example 3: Concave Mirror
- Select "Concave Mirror", f = 120 px. Object beyond C (2F) gives real, inverted, diminished image in front of mirror.
- Object inside F: virtual, upright, enlarged image behind mirror.
Frequently Asked Questions
What sign convention is used?
Cartesian sign convention. Light travels left to right. Object distance positive if object is on incident side. Focal length positive for convex lens/concave mirror, negative for concave lens/convex mirror.
How do I know if the image is real or virtual?
Positive image distance = real image (opposite side for lens/mirror). Negative = virtual. The ray diagram shows solid rays for real, dashed for virtual.
Can I change object height?
Yes, use the Object Height slider. The image height scales according to magnification.
Why does the image disappear when object is at focus?
When u = f, the rays emerge parallel, and the image forms at infinity (v = ∞). No finite image is drawn.
Does this cover thick lenses or aberrations?
No, this is an ideal thin lens / spherical mirror model with perfect focusing. No chromatic or spherical aberrations.