Alternatively, a single stand can be placed in front of the mirror, and strings attached to nails along the top. Invite student volunteers to stretch out the strings as rays that converge at the location of the image. Then show that the you can put the second stand at the point where the strings meet and it lines up with the image.

Engagement Suggestion

• • The box is first shown to the group. Then the black cloth is placed over the front of the box, the trap door on top of the box opened, and the rabbit put into the box through the trap door.
• • Invite students to predict what they will see when the cloth is removed.
• • When the black cloth is removed the rabbit has vanished into thin air (behind the mirror).
• • Challenge then to analyze how this has happened
• • Explain the positioning of the mirror, and invite them to consider what it would look like with the mirror at different angles.

Background

Background

A single square array of small lights has a full-silvered mirror in back and a half-silvered mirror in front. A long black box placed in back of the infinity mirror appears to have many rows of lights in it until it is removed!

An interesting sidelight is to use this device to indicate the dynamic range of the eye. Each successive row of lights has an intensity of about 1/2. Approximately twenty rows of lights can be seen by the typical naked eye, so the dynamic range of the eye is at least as great as 2^20, or 1,048,576 to 1.

The large box has holes in each end for people to insert their heads, and a half-silvered mirror in the middle. A special variac has been wired so that when the knob is turned lights in each end of the box change intensity with one getting brighter while the other gets dimmer, and vice versa. Each viewer will see a metamorphosis of his or her face to that of the person on the other side. This device was made by an art student as a class project and donated to the Lecture-Demonstration Facility.

A second hole in one end allows the action to be viewed by a video camera and displayed for the entire class, as seen in the photographs below.

This is a smaller, more easily portable version of demonstration L2-22, suitable for use in small classrooms. A ring of lights is repeatedly reflected by a rear mirror and a partially silvered front window, creating the illusion of lights vanishing into the distance.

A ray of light strikes the two surfaces of the corner reflector and returns antiparallel to the original light ray. For a three-dimensional corner reflector the outgoing light ray also leaves antiparallel to the incoming light ray. The lens keeps the ray narrow.

A set of three rays of different colors can also be used with this two-dimensional corner reflector to show that the rays return inverted with respect to their initial orientation.

The laser is mounted on a stand with the beam coming out a hole in the white baffle, and aimed across the room or to the rear of the lecture hall. Hold the corner reflector in the beam and the reflected beam will return to be easily seen on the white card. Rotate the corner reflector and change its angle, showing that the beam still returns to the card. The specular reflection of the laser beam off the front surface of the glass will also be seen moving around the room.

Background:

This mirror element is of the type used to construct the reflector for the lunar ranging experiment, you can read more at TERP: Mirrors on the Moon and Big Think: We Use Lasers To Keep Track Of The Moon.