Demo Videos: Optics

Demonstration videos illustrating key concepts of light and optics.

For other videos from our demonstration collection, please visit Physics Demo Videos. You may also wish to view our Video Lecture Series for short tutorials on topics from first year physics.

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Reflection and Refraction
Total Internal Reflection — Aquarium. When light travels from a denser to a less dense medium, such as water to air, there is a critical angle of incidence beyond which the light will be total internally reflected at the internal surface of the water rather than refracted out into the air.
Total Internal Reflection — Blackboard Optics. When light travels from a denser to a less dense medium, such as plastic to air, there is a critical angle of incidence beyond which the light will be total internally reflected at the internal surface of the plastic rather than refracted out into the air.
Fiber Optics: Lucite Curl. Fiber Optics work due to total internal reflection. A curl made of Lucite will still emit light at the other end. Were it not for scratches, we would not see any light emerging from the sides of the rod.
Fiber Optics: Multi-Strand Cable. Fiber Optics work due to total internal reflection. A cable can even be tied in a knot and the light will still be emitted by the other end.
Disappearing Beaker. Pyrex and Wesson oil have the same index of refraction. Thus, a small test tube filled with oil set into a larger container of oil will “disappear”.
Mirrors and their images
Flat Mirror: Blackboard Optics. On a flat mirror, the angle of incidence is equal to the angle of reflection.
Concave Mirror: Blackboard Optics. A concave mirror reflects parallel light rays through the same point. If the center ray strikes normal to the mirror, the place where the rays converge is called the focal point.
Convex Mirror: Blackboard Optics. When parallel rays strike a convex mirror, the reflected rays diverge as if emanating from a point on the opposite side of the mirror.
Concave and Convex Mirrors. Images in concave mirrors are upright and have magnification less than 1. Concave mirrors may produce an image that is either upright or inverted and that is larger or smaller than the object, depending on the object’s location. Watch what happens to the image as the student approaches the concave mirror.
Contraconcave Mirrors (Mirage). wo concave mirrors facing one another can be used to create an image that appears to float in air.
Lenses and their images>
Converging Lens: Blackboard Optics. A converging (convex) lens focuses light through a focal point before creating a magnified image.
Diverging Lens: Blackboard Optics. A concave lens bends parallel rays apart, as if they were emanating from a point on the object side of the lens.
Aquarium optics. An air-filled convex lens in water acts as a diverging lens!
Large Convex Lens. This lens is held less than a focal length from the instructor’s face. The image is upright and magnified. The image is initially upright and magnified. At full arm extension, the image becomes inverted.
Interference and diffraction
Slit Diffraction. Interference between light waves coming from different slits will produce interference patterns imposed on the single slit diffraction pattern. The video starts with single slit, then shows double and triple slits.
Diffraction grating. Hundreds of evenly spaced slits make a diffraction grating. Due to the regular small slits in a diffraction grating, light can be broken down into its constituent colors through interference. For this source, there seem to be three distinct lines; a red/orange, a faint green and a faint blue.