Geometrical Optics Topic

Straight Line Propagation

Concept 1 demo

Three-panel image: (left) Mini Maglite with wooden bar casting a sharp shadow on the wall, (center) round frosted bulb with the same bar casting a diffuse shadow, (right) tall clear filament bulb with the bar held horizontally

Shadows

Students observe how source geometry determines shadow sharpness. A point source (Mini Maglite) casts sharp shadows; an extended source (frosted bulb) produces penumbra. A tall clear filament bulb shows orientation-dependent …

Reflection from Flat Surfaces

Concept 11 demos

White optics board with ray projector at left edge projecting a single ray that reflects off a black plane mirror mounted magnetically on the board

Blackboard Optics Plane Mirrors

Visible light rays reflect off plane mirrors on the blackboard optics board, demonstrating. Mirrors can be combined to build periscopes, corner reflectors, and other multi-mirror systems.

Green laser pointer mounted in a clamp on a blue stand, aimed at a flat mirror lying on the table; green incident and reflected beams form an X pattern on the mirror surface; fog machine with red button visible behind the mirror

Laser and Mirror

A green laser aimed at a flat mirror demonstrates the law of reflection . Fog or chalk dust makes the incident and reflected beam paths visible, giving students direct visual …

View through glass tank showing a bright lamp reflected in rippled colored water, with the reflection elongated into a vertical streak

Rippled Reflection

Students observe how rippled water transforms the reflection of a point light source into a vertical pillar of light, demonstrating that the law of reflection applies locally at each surface …

Reflection from Curved Surfaces

Concept 7 demos

Five parallel rays from the ray projector on the left reflect from a concave mirror block on the right, crossing at different points and showing caustic formation on the magnetic blackboard

Blackboard Optics Curved Mirrors

Parallel light rays from a ray projector reflect from concave and convex mirror blocks on a magnetic blackboard, allowing students to directly observe focal points, spherical aberration, and caustic curves. …

Gold mirrored sphere on a gray surface with a stuffed animal placed beside it; the sphere's reflection shows the room and objects distorted by the convex curvature

Mirrored Sphere

A polished spherical mirror produces virtual, upright, and distorted images. Students observe how the curved surface compresses a wide field of view and explore anamorphic projection — placing a pre-distorted …

Half-open wooden box with large concave mirror visible through the opening; a white rose appears to stand upright in a clear glass with blue marbles on the wooden lid

Concave Mirror Real Image

A concave parabolic mirror creates a real image of hidden upside-down roses that appears upright inside a glass, demonstrating real image formation by curved mirrors. Students see that real images …

Refractive Index

Concept 4 demos

Tilting metal frame with two glass vials connected by tubes, tilted so oil fills the right vial; colored letter cards (A, B, C, D) are placed behind each vial for comparison

Disappearing Glass

Demonstrates index matching: when two transparent materials share the same refractive index, light crosses their interface without refraction or reflection, making the boundary invisible. Students see this dramatically as glass …

Green laser beam entering a rectangular water tank from the left, curving downward then bouncing back up through the sugar-gradient water, against a black background

Bouncing Laser Beam

A sugar density gradient in water creates a continuous variation in refractive index. A laser beam curves toward higher-density regions and undergoes total internal reflection, producing a visible bouncing path. …

Textbook diagrams showing the Schlieren optical setup: perspective view of light source, mirrors, and knife edge arrangement, plus two schematic cross-sections of single-mirror configurations

Schlieren System

Makes refractive index gradients in air visible using a mirror-based knife-edge technique. Students observe how temperature variations cause density changes that bend light, and can distinguish laminar from turbulent flow …

Refraction from Flat Surfaces

Concept 6 demos

$Single light ray refracting through a tilted rectangular plexiglass block mounted on paper on the blackboard, with ray projector visible at left edge$

Blackboard Optics Refraction at Flat Surfaces

Students observe how light rays bend when entering and exiting transparent plexiglass blocks, verifying Snell's Law quantitatively by tracing rays on paper. The setup also demonstrates total internal reflection and …

$Semi-circular acrylic block on blackboard optics board with a light ray entering the curved surface along a radius, refracting at the flat surface with a partially reflected ray visible$

Blackboard Optics Semi-Circular Block

Demonstrates Snell's law and total internal reflection using a semi-circular block on the blackboard optics board. Rays directed along radii enter the curved surface at normal incidence (no refraction), isolating …

$Side view of Leybold refraction apparatus: lamp housing on stand behind a water-filled glass vessel containing a disk, with red-corded transformer on the bench$

Leybold Refraction Apparatus

Visualizes Snell's Law at a flat water-air interface. The multi-slit diaphragm shows refraction, the critical angle, and total internal reflection simultaneously across a range of incidence angles.

Total Internal Reflection

Concept 8 demos

$Triangular plexiglass prism on magnetic blackboard with ray entering from left, refracting into the prism, then partially reflecting and partially refracting at the hypotenuse face$

Blackboard Optics Total Internal Reflection

Students observe total internal reflection using plexiglass blocks and a ray projector on a magnetic blackboard. Any of the available block shapes (triangular, semicircular, rectangular) can be oriented to demonstrate …

$Complete setup with laser and rotating mirror mount on left, water tank on wooden block on right; green beam enters the water from below, reflects and refracts at the water-air surface$

Rotating Mirror beside Water Tank

Students observe total internal reflection at a water-air interface by sweeping a laser beam through a range of incident angles. The reflected beam visibly brightens as the angle approaches critical, …

Small translucent ulexite specimen (~1x1x2 cm) resting on a large white letter A on a red background, with part of the letter's edge visible through the top of the stone

Ulexite: Fiber Optic Rock

A naturally occurring "fiber optic rock" transmits images from its base to its top surface via total internal reflection in parallel crystal fibers. Comparing ulexite to a plain acrylic block …

Rainbow

Concept 3 demos

Kodak carousel slide projector on a wooden platform at left, water-filled spherical flask at right, with a rainbow arc visible on a white screen mounted on a ring stand above

Rainbow

A water-filled spherical flask models a giant raindrop. Students observe rainbow formation through refraction at entry, internal reflection off the back surface, and refraction at exit — with dispersion separating …

CD mounted in finger clamp on optical stand with a fiber optic white light source aimed at the data side, producing a rainbow spectrum and bright specular reflection on the wall behind

CD Rainbow

A CD's data tracks (spaced at) act as a reflection diffraction grating, separating white light into a vivid spectral rainbow on the wall. Students see that periodic structures produce wavelength-dependent …

$Small circular acrylic disk on blackboard optics board with white light beam entering from the left, producing a dispersed rainbow spectrum to the upper left and a refracted beam to the upper right$

Blackboard Optics Rainbow

A plexiglass semicircular block or small disk on the blackboard optics board demonstrates dispersion, refraction, and total internal reflection — the three phenomena that produce rainbows in water droplets.

Thin Lens

Concept 7 demos

Five parallel light rays from a ray projector on the left passing through a biconcave (diverging) lens mounted on a magnetic board, diverging outward on the right side

Blackboard Optics Lenses

Uses a multiple-ray projector on a magnetic board to show ray behavior through converging and diverging lenses. Students see focal points, ray tracing rules, compound lens systems, and aberrations in …

Large convex lens clamped to a vertical rod on the lecture bench with a gray mounting plate, two illuminated desk lamps on a wooden stool positioned below

Convex Lens

Demonstrates real image formation with a convex lens and directly addresses the common misconception that different parts of a lens form different parts of the image. Blocking half the lens …

Lecture hall with translucent screen on left showing inverted real image of a glowing lamp filament, large convex lens on tripod in center, and boxed lamp visible in background right

Convex Lens and Lamp

A large convex lens (f = 220 cm) projects a real, inverted image of a lamp filament onto a screen. Students directly observe real image formation and can verify the …

Pinhole

Concept 4 demos

Full setup: translucent screen at left, multicolor LED tower on stand at center, incandescent light bulb in wooden box at right, with bar clamp, lead brick, and masks on bench

Introducing a Pinhole

A sequential progression from shadow casting through slit projection to pinhole imaging. Students build intuition for rectilinear propagation, image inversion, and the pinhole camera principle by drawing ray diagrams at …

Screen showing dozens of inverted filament images projected through pinholes in aluminum foil, with the large lens visible at bottom

Pinhole Projection

Multiple pinholes in aluminum foil each project an independent inverted image of a lamp filament, demonstrating rectilinear propagation. A large converging lens then collects all pinhole images into a single …

Nikon DSLR camera body on green surface with a metal pinhole mount assembly attached and two interchangeable metal pinhole plates laid out beside it

Digital Pinhole Camera

Shows that images can form without lenses through geometric projection alone. Students observe the trade-off between aperture size, image sharpness, and brightness using interchangeable pinhole plates on a digital camera.

Thick Lens

Concept 9 demos

Row of Wittner mechanical metronomes on a lab bench shot from low angle; the nearest red-and-white metronome is sharp while background metronomes progressively blur

Depth of Field

Shows how lens aperture controls depth of field — the range of distances that appear in focus simultaneously. Students see the trade-off between light gathering (wide aperture) and depth of …

Large-format wooden view camera with ground glass plate on an optical bench, with a lamp covered in aluminum foil (pinholes visible) to the right

Depth of Focus

Demonstrates how aperture size controls depth of focus. Students observe that reducing the aperture of a camera allows pinholes to remain in focus over a wider range of image-plane positions, …

Large plano-convex lens in holder projecting an image of the fiber optic cable end onto a screen, showing color fringing with orange and white edges from chromatic aberration

Chromatic Aberration of a Lens

Students observe that a simple plano-convex lens cannot simultaneously focus red and blue light, demonstrating chromatic aberration from wavelength-dependent refraction. Comparing with an achromatic projection lens shows how doublet designs …

Optical Instruments

Concept 9 demos

Video camera with flip-out screen at near end of optical bench, convex lens in dark card mount in middle, desk lamp illuminating target card at far end, wooden meter stick along bench

Microscope Model

Two convex lenses on an optical bench model a compound microscope, producing a magnified, inverted image captured by a video camera. Students see how objective and eyepiece lenses combine for …

Boreal 420T stereo microscope with digital camera mounted on top, single eyepiece tube visible, focus knobs, chrome stand, and white LED-illuminated base with circular stage

Microscopes

Demonstrate compound microscope optics as a concrete application of multi-lens image formation. Both microscopes have digital output for classroom projection, allowing the whole class to observe magnified samples in real …

Blackboard optics microscope configuration: ray projector on left sends diverging rays through two magnetic convex lenses on a chalkboard, with chalk annotations labeling points A, B, A-prime, B-double-prime, and "to eye"

Blackboard Optics Microscope and Telescope

Demonstrates compound microscope and refracting telescope configurations using magnetic blackboard optics. Students see how two-lens systems form intermediate and final images through visible ray tracing, connecting lens equations to observable …