Geometric Optics Lab
Select a lens or mirror, adjust object distance and focal length, and watch the ray diagram update in real time. Record measurements to verify the thin lens equation and explore how image properties change with object position.
Guided Experiment: Converging Lens Image Formation
As you move an object from far away toward the focal point of a converging lens, what do you predict will happen to the image distance, size, and orientation?
Write your hypothesis in the Lab Report panel, then click Next.
Ray Diagram
Controls
Results
Data Table
(0 rows)| # | Trial | Element | d_o(cm) | f(cm) | d_i(cm) | M | Image Type |
|---|
Reference Guide
Thin Lens / Mirror Equation
The fundamental equation of geometric optics relates the object distance d_o, image distance d_i, and focal length f for both thin lenses and spherical mirrors.
Rearranging to solve for image distance gives d_i = (f × d_o) / (d_o − f). When d_o equals f, the image forms at infinity (parallel rays).
Magnification
Magnification M describes both the size and orientation of the image relative to the object.
When |M| > 1 the image is enlarged. When |M| < 1 the image is diminished. The sign of M tells you the orientation: M > 0 means upright (virtual image), M < 0 means inverted (real image).
Sign Conventions
Converging lenses and concave mirrors have positive focal lengths (f > 0). Diverging lenses and convex mirrors have negative focal lengths (f < 0).
A positive image distance (d_i > 0) means the image is real. For lenses, real images form on the opposite side from the object. For mirrors, real images form on the same side as the object.
A negative image distance (d_i < 0) means the image is virtual and cannot be projected on a screen.
Principal Ray Tracing
Three principal rays locate the image for any lens or mirror configuration.
Parallel ray (red) travels parallel to the axis and refracts/reflects through the focal point.
Focal ray (blue) passes through the focal point on the object side and emerges parallel to the axis.
Center ray (green) passes through the center of the lens (undeviated) or the center of curvature of a mirror (reflects back on itself).
The intersection of any two rays locates the image. Virtual images are found by extending rays backward (dashed lines).