Focus the TV camera on the image of its lens created by the concave mirror (or the "X" printed on a paper mounted on the lens). Move the ruler toward the mirror until it is in focus, demonstrating that the image is at that point. The pictures below show the meter stick too close to the camera, at the focus of the camera, and too close to the mirror. The background consists of a large amount of unrelated physics demonstration equipment.

Students can stand in front of the concave side at different distances to find the focal point. Invite students to predict the orientation of the image they see at different points, then try it out.

In small classes, this can be passed around to students. Challenge them to come up with ways to determine the focal length.

Invite different students to view the tank from different angles and draw what the rod looks like. Have them compare their experiences and discuss.

The rays refracting in the horizontal and the vertical planes bend differently when exiting the dish, causing the ball bearing to become distorted when viewed through the top surface of the water.

It apparently is a non-trivial problem to show that the image produced by a horizontal fan of rays is not at the same location as that produced by the more easily handled vertical fan of rays.

A laser beam is spread into a horizontal line by a cylindrical lens, and passes over a current-carrying wire aligned along the original laser beam. The hot wire causes the air to have a very strong decreasing temperature gradient a long the central section of the laser light line, so that section bends upward. The bent laser line is displayed on the wall or screen across a long distance (perhaps the width of the room), as seen below.

Upward bending of blue light from the sky as it propagates along sun-heated sand in the desert causes blue light to appear to be coming from the ground, creating the classic illusion of a lake in the desert.

A video camera is optionally available to make this more visible in large lecture halls.

By measuring the minimum angle of deviation a for a microwave beam passing through an equilateral paraffin prism, the index of refraction N can be calculated:

N = 2 sin ( 30 degrees + a / 2 ).

Rotate the semicircular slab of plexiglass with the light ray entering and exiting through the curved surface. Starting with the ray incident nearly perpendicular to the flat internal surface, rotate the semicircular slab until the critical point is reached and total internal reflection is obtained. Reflection at entrance can be avoided by having the light enter perpendicular to the surface. A single slit baffle and convex lens are used to produce a narrow ray of light.

The Brewster angle can also be demonstrated by rotating the semicircular slab so that the transmitted refracted ray and the internally reflected ray are perpendicular. See Demonstration M7-11: OPTICAL BOARD - BREWSTER'S ANGLE.