Category Archives: Interference

Two-Liter Thin Film Interference

Demo: OP-D-TL
Pira Index: 6D 30.20

 Lab Equipment  Directions
  1.  2 liter soda bottle with small amount of soap solution
  1.  With your palm over the opening swirl the solution to cover the inside of the bottle, including the opening.
  2. Tip the bottle upright and slide your hand off the opening leaving a thin film across the opening.
  3. Remove the cork from the bottle side and gently blow through the top opening, pushing the bubble down from the neck to the middle of the bottle.
  4. Replace the cork and observe changes in the thin film as time passes.



Thin Film, OHP

Demo: OP-D-TF
Pira Index: 6D 30.20

 Lab Equipment  Directions
  1.  clear plastic tray
  2. white ice cream bucket
  3. soap bubble solution
  4. plastic blowing tube
  5. overhead projector
A good soap solution can be made as follows: 1 part dish detergent, 2 part glycerine, 3 parts water
  1.  Place the plate on the overhead to illuminate bubble (not for projecting onto screen).
  2. Pour small amount of solution onto the center of the plate. Dip the end of tube into the puddle and blow gently to create a bubble dome. By continuing to blow you can get a 6″ bubble.



Speckles on the Wall

Demo: OP-D-SW
Pira Index: 6D 20.75

 Lab Equipment  Directions
  1.  Spectra Physics 248 high-powered laser and power supply strapped to white board with magnet strip and lab jack
  2. 18 mm lens and steel lens holder
  1.  Use the lens to spread the beam of the laser and direct the spread beam at a wall.
  2. Look at the speckles on the wall. Move your head right or left and see which way the speckles move (those far-sighted and near-sighted will see them move in opposite directions).
  3. Near-sighted people will also be surprised to find that if they remove their glasses the speckles are still in focus.



Michelson Interferometer

Demo: OP-D-MI
Pira Index: 6D 40.00

 Lab Equipment  Directions
  1.  Interferometer
  2. laser
  3. Pasco lab bench – long
  4. magnetic lens holder
  5. mounted lens
  6. mirror on laser support with sponge
  7. plug strip
the mirror is used to bounce the bull’s eye pattern onto the wall at a higher location so that students can see it better.
  1.  Set laser and interferometer on bench as shown, do not include lens and holder on bench.
  2. Align laser so that beam goes through small round glass on interferometer hitting the mirrors on either side of the glass.
  3. On a screen situated to the left side of the bench you should see two small laser dots. Adjust the indicated screws to bring the dots together to result in 1 dot.
  4. Place the lens so that the beam spreads out over the round glass. Turn the indicated knob to see the bulls eye pattern.



Morpho Butterfly

Demo: OP-D-MB
Pira Index: 6H 35.53

 Lab Equipment  Directions
  1.  Brown box with butterflies
  1.  Open carefully and look at the wings. The color is not created by pigment inside the wing, but by interference of light reflected from thin film on wings.



Light Diffraction, OHP

Demo: OP-D-LD
Pira Index: 6D 20.20

 Lab Equipment  Directions
  1.  File folder with slit
  2. 4″ x 4″ holographic grating in frame with stoppers for support
  3. overhead projector
  1.  Place the folder on the overhead and focus.
  2. Hold the holographic grating over the top lens of the projector. You should see a light spectra to each side of the slide.



Interference Patterns, OHP

Demo: OP-D-IP
Pira Index: 6D 10.00

 Lab Equipment  Directions
  1.  Interference patterns for overhead projector
  2. Moire patterns
  1.  Lay sheets on overhead and align the pattern.
  2. Offset the sheets one wavelength at a time and watch the change in the interference patterns.



Filament Spectrum

Demo: OP-D-FS
Pira Index: 6D 20.00

 Lab Equipment  Directions
  1. Showcase bulb and socket
  2. Variac
  3. Diffraction grating 3 paneled screen
  1. Place the screen in front of the bulb. Plug the bulb into the variac, turning it up until the bulb glows brightly.
  2. Observe the spectrum through the screen.
  3. Turn down the variac and as the bulb cools, notice the loss of the blue end of the spectrum.