Wave Optics

Interference Model

Concentric circles drawn on two transparent plastic plates can be used to show the interference patterns caused by two interacting wavefronts. They are placed on an OHP to display interference patterns on a large screen.

Michelson Interferometer

The study of the Michelson interferometer has historical importance. This interferometer can be used for measuring the wavelength of monochromatic light with an accuracy better than 5% and for making precise measurements of the refractive index of air.

List of parts:
  1. Interferometer
  2. Laser with diffusing lens
  3. Big lab jack
  4. White screen
Notes:

Newton's Rings

We have a small (54mm in diameter) demo apparatus, which can be passed between the students. They will see a series of concentric light and dark rings centered at the point of contact between the spherical surface of a lens and the surface of flat glass. Three cap screws can compress the frame and squeeze the two pieces of glass thereby changing the observed patterns. The patterns are best viewed in reflected, monochromatic light. In daylight students will see rings of rainbow colors.

Note: The rings produced by this apparatus are very small(∅ 3-4 mm), therefore this demo is not useful for large classes. It is good in labs, especially when a microscope with monochoromatic light is available to students.

Diffraction Gratings

Large diffraction grating. The grating (see picture to the right) has 1600 grooves/mm and is used with a bright light source (arc lamp) to obtain a spectacular continuous spectrum. The first and second order spectra are easily seen, while the third can be seen when the lights in the auditorium are dimmed.
This highly reflective diffraction grating is secured in a homemade holder with a protective lid and is attached to a Swiss-made survey protractor. Changing the angle of the protractor results in a spectrum shift. Placing a piece of black paper with a slot on the spectrum while shifting it can show to the students how monochromators work.


Diffraction grating slides: We also have 200 small slides with diffraction gratings (536 grooves/mm) that can be distributed between students to observe spectra from discharge tubes and other light sources.

Thin-Slit Diffraction

Our two adjustable slits unit is a precisely-made part from an old spectrometer. The mechanism that changes the slits' width is shown in the picture to the left. The unit can be used in either vertical or horizontal position. A common setup with the laser, slit unit, and a lab jack is shown to the right. Students can see the spectacular, bright red diffraction patterns when lights in the auditorium are dimmed.

Cornell Grating Slide

This is a slide with a variety of single and double slits of various widths and spacings. Also in the middle of the slide there are several diffraction gratings with different number of slits per millimeter. Use this with a laser and project the diffraction pattern onto a screen.

Microwave Optics

The microwave optics kit consists of a microwave transmitter and receiver, a goniometer, and parts for a number of experiments. Both the transmitter and receiver operate at the 3 cm wavelength. All parts are shown in the pictures.

Experiments for demonstration:
  1. Polarization
  2. Single slit diffraction
  3. Double slit interference
  4. Bragg's diffraction (with the styrofoam cube with 100 metal spheres which simulates a crystal lattice)
Note: The receiver is powered by two 9-Volt batteries; make sure to switch it off after the demonstration.

Large Polarizers

We have three linear polarizers with arrows showing the angle of polarization. The polarizers can be put on stands with two or three slots, as shown in the picture.

Brewster's Angle

The demonstration of Brewster's angle is shown in the pictures.

List of parts:
  1. Strong light source (arc lamp)
  2. Framed glass
  3. Protractor
  4. Large polarizer on a jack stand
Notes:

Finding Stress Areas with Polarizers

This is a good demonstration to show one of the applications of polarized light and to observe beautiful, colorful patterns. This simple method is employed by industrial manufacturers to assure quality control of plastic and glass products. The device (see picture to the left) consists of a light source and a matte screen for uniform illumination. A big polarizer is placed on top of the screen and can be rotated by hand, while a small polarizer can be slid up into place to accommodate a range of objects. Areas of stress will be revealed when an object is placed between the polarizers (see pictures below).
   

Karo Syrup Between Two Polarizers

Karo syrup in a glass bottle is placed between two polarizers. A light bulb on a small jack is positioned behind the polarizer stand (see picture to the left). As one of the polarizers is rotated, students can see spectacular colors.

Rotation of the Direction of Polarization with Dispersion

A spectacular spiral rainbow can be seen in a sugar column. When the polarizer underneath the column is rotated, the spiral rainbow also rotates.

List of parts:
  1. Acrylic tube with sugar solution
  2. Source of bright, collimated light
  3. Polarizer
  4. Black skirt
  5. Variac
Notes:

Polarization from Scattering


The polarization of scattered light can be shown by shining light through milky water and rotating a large polarizer in front of the water tank (see pictures).

List of parts:
  1. Rectangular glass tank filled with water mixed with milk powder
  2. Source of strong white light (arc lamp or slide projector)
  3. Large polarizer on stand

Fluorescence

We have a set of 5 mounted vials with fluorescent liquids and various fluorescent rocks. Each vial and rock glows a different and brilliant color when placed under ultraviolet light (see pictures).
 

Additive Color Mixing

This apparatus can create primary and secondary colors, and their combination with 3 filters, overhead projector, and 3 mirrors on a tall stand.

Procedure:
  1. Place the plate with colored filters on the OHP and project the circles onto the mirrors so that they will make three circles on the screen.
  2. Use screws on the mirrors to adjust the position of the red and blue circles. You should get white light where the three overlap.

Rainbow Demo

A spherical flask filled with high-index liquid simulates a large water droplet and projects a beautiful rainbow on a white cardboard screen when colimated white light is shined at it. This setup (shown to the left) is home-made, but the idea is copied from the UCB Physics Lecture Demonstrations catalog. A detail image of the rainbow is shown below (center).

To demonstrate the reflection and refraction inside of a water droplet we use a laser and 6L round flask filled with water.

List of Parts:
  1. Carbon arc lamp on a jack
  2. Framed cardboard screen (white on one side and black on the other) with a 50mm round hole in the center
  3. 100 mL round flask filled with Ethyl Cinnamate clamped to a stand
  4. 6L round flask filled with water with a bit of colloidal silver.
  5. Red or green laser on stand
Note: Position the flask between the light source and the students.

Scattering and Color

This demonstration addresses the questions: "why is the sunset red?," and "why is the day sky blue?" When light from the bulb passes through the dry milk in water it simulates the scattering of sunlight in the atmosphere during the sunset. The jack should be adjusted (see pictures) so the students can compare the colors of the filament and of the scattered light (picture to the left).

List of parts:
  1. Unfrosted bulb in a ceramic socket
  2. Square glass tank filled with water and dry milk
  3. Lab jack
  4. Variac
Note: Put enough dry milk so that the filament of the bulb appears to be red as you look at it through the water.

Linear Spectra

We have a set of 5 discharge tubes filled with different gases (H2, He, Hg, Ar, and Ne - see picture of 4 of them to the right). When the discharge tube is turned on students can observe linear spectra with the help of small plastic slide-like diffraction gratings. There are enough gratings to pass around for a large class.


Spectrum of Neon