My PBL Project-Diffraction (rainbow glasses)

INTRODUCTION:

What causes the color of a rainbow to appear when you look at a light bulb through a pair of rainbow glasses?

The diffraction of rainbow glasses is to find what causes the color of a rainbow to form through rainbow glasses. Through a pair of rainbow glasses a rainbow should appear around the light bulb. the interference and diffraction meaning the rainbow is a beam of light waves through the glasses.

MATERIALS:

1. Rainbow glasses

2. Red laser

3. Incandescent or other white-light ray box

4. Transmissive diffraction grating (300-600 lines/mm)

PROCEDURE:

The first thing you have to do is gather your materials listed above.

Take pictures of the materials, and shine the laser through the small slits.

You're going to want to write down the pattern that is on the wall that the diffraction grating makes. You figure out what the diffraction and the interference and the same with the regular light you shine through. Final thing is shine the regular light through the diffraction grating as well as the laser beam.

SCIENTIFIC PRINCIPLE/ ESSENTIAL UNDERSTANDING:

What causes the colors of a rainbow to appear when you look at a light bulb through a pair of rainbow

glasses?

Over the centuries, our view of light has changed dramatically. The first real theories about light came from the ancient Greeks. Many of these theories sought to describe light as a ray -- a straight line moving from one point to another. Pythagoras, best known for the theorem of the right-angled triangle, proposed that vision resulted from light rays emerging from a person's eye.

The size of a wave is measured as its wavelength, which is the distance between any two corresponding points on successive waves, usually peak to peak or trough to trough. The wavelengths of the light we can see range from 400 to 700 manometers (or billionths of a meter). This was Einstein's explanation: If the energy in light comes in bundles, then one can think of light as containing tiny lumps, or photons

Safety Regulations:

* Do not look directly at the bright lights or at the sun

* Do not look into any laser beam or stray reflection of a laser beam

this may cause permanent damage!!!!

Driving Questions

1) What is Huygens Principle and how can it be used to explain why interference and diffraction occurs in waves when they pass through small slits?

Huygens Principle was developed by Christian Huygens and explains laws of ‘geometric optics’. This says that points on a wave front are the sources of secondary waves that spread in all directions. Imagine ripples in water, but along a straight, uniform line. Diffraction occurs when the wave goes through a slit because the wave treats the slit as a new source to ripple from. This is why a voice from a different room sounds like it is from the doorway itself.

2) If a transmissible diffraction grating is simply a piece of transparent medium with many small, closely-spaced dark lines on it, how does it produce an interference and diffraction pattern?

The many holes in the medium provide for many separate wavelets to be produced. When the wavelets begin to intersect with each other, a pattern is formed.

3) Hold the diffraction grating 1 m in front of a wall, and shine the laser through it so the interference and diffraction pattern projects onto the wall. Describe the pattern of laser light after it passes through the diffraction grating.

The pattern on the wall after going through a diffraction grating causes light and dark areas to appear in stripes on the wall.

4) What causes the bright and dark areas in the laser's interference and diffraction pattern?

When the waves overlap after going through the grating, they interfere with each other and create ‘bright fringes’ when the waves intersect

5) Describe the interference and diffraction pattern of a ray of white light after it passes through a diffraction grating. Why doesn't the interference and diffraction pattern of the white light show as many bright and dark areas as the laser's interference and diffraction pattern? What does it show in place of the bright and dark spots?

When a white light, like a bulb or the sun’s light, is shown through a diffraction grating, a series of colors, ranging from violet and blue near the source of light and green orange and red farther away from the light, shall be shown.

6) Look through the rainbow glasses at any white light source. How does the pattern you see when you look through the rainbow glasses compare to the pattern you observed through the diffraction grating? What is similar and why? What is different and why?

Through my understanding of diffraction and interference, I find that the rainbow-like colors revolve around a central bright point because that point is the ‘slit’ in the diffraction grating. The point of light is allowed through and is diffracted or bent to form the pattern seen with the rainbow glasses.

Extension and Synthesis Questions

When you observe the interference and diffraction pattern of white light through a diffraction grating, the pattern is always mirrored about a central bright point. Why does the pattern mirror itself about that point?

Through my understanding of diffraction and interference, I find that the rainbow-like colors revolve around a central bright point because that point is the ‘slit’ in the diffraction grating. The point of light is allowed through and is diffracted or bent to form the pattern seen with the rainbow glasses.

When you observe the interference and diffraction pattern of white light, why are the colors always in a very specific repeating order?

The violet and blue light is closer to the ‘central maximum’ than the other colors like green, yellow, orange and red. As the waves bend away from the maximum, those other colors appear.

Often the interference and diffraction pattern of white light will appear condensed about the central bright white point, as in the top image. What can you change to spread the pattern out so the colors don't blend together, similar to the lower image?

Changing the distance from the lighting and the concentration of the light on the diffraction grating will change the spread of the pattern to get a greater effect.

Imagine you were observing an interference and diffraction pattern of white light that has been spread out using the procedure outlined in your answer to the previous question. Why are there dark areas just before the color violet, and just after the color red?

Possibly once the distance and concentration were increased, the light began to act similar to the laser light and leave gaps in the pattern and the waves had less area to spread out to and a larger area to do so, so interference between the waves caused breaks in the color.