One of the most fundamental properties of science are that experiments are replicable. One such experiment that has stood the test of time, in terms of replicability and correctness, is Young's double slit experiment, that is until Einstein came along. It wasn't incorrect per se, but it was incomplete. Young's experiments proves that light behaves like a wave, whereas during his time, the accepted theory was that light is a particle, as Newton had backed this idea. It was not until Einstein came along with his Noble Prize winning experiment, that he proved that light behaves like a particle as well, and combining this with Young's theory and proven experiment, we got the Wave-Particle-Duality concept to describe and define the definition of light. This concept is still used today and is the current accepted definition for the behaviour of light.
As this project is focused on a science experiment, I have decided to format it loosely similar to a science paper following the scientific method, as well as written in past-passive terms.
Step 1: Safety Precaution
Lasers are very dangerous to the human eye. Do not shine directly onto the eye or look at the laser. Always wear laser safety goggles, which is different from sunglasses.
As I was working close to a door, I have also placed a Danger sign on my door, to prevent other people from opening the door, interfering with the experiments, and more importantly preventing potential safety hazards.
Step 2: Background: Young's Wave Theory of Light
The wave theory predicted that light waves could interfere with each other like sound waves or water waves. Thus, producing patterns of constructive and destructive interference. Explicitly, this entails that given a beam of photons, shone on two slits, in this case slits that are very small they are not visible to the human eye, like that in a CD, the light will produce patterns of light and dark spots, rather than two distinct areas of individual particles.
Step 3: Purpose of Experiment
- The purpose of the experiment was to analyze the behaviour of light and demonstrate the wave nature of light.
- Furthermore, for the purpose of scientific curiosity, given the theory proven by young and wavelength of light, the distance between data points, i.e. slits of a CD, will be calculated from theory.
- Light exhibits a wave-like nature similar to that of sound waves.
Step 4: Materials and Apparatus
- Laser Pointer
- Power Source or Batteries
- Old CD
- Tape Measure
- Clear Tape
- Large empty wall
- Safety Glasses
Step 5: Experimental Setup
- The CD was carefully cut using a pair of scissors, radially towards the centre.
- The top layer of the CD was peeled off starting from the cut-point using finger nails, and subsequently, given some portion of the CD has been removed, it was peeled off clear tape.
- The Laser was plugged in to a 3V power source.
Note: In this case, the laser pointer was broken, so two pieces of jumper wires were used, which were soldered to the cathode and anode respectively, and connected to a power sources. Normally, two AAA batteries will suffice which will also provide a total of 3V, connected in series.
Step 6: Procedure
- The laser pointer was setup at some distance from the CD's diffraction gratings, and this distance was recorded for experimental calculation purposes.
- The CD was secured such that it will not move for the duration of the experiment and at a distance from the wall, which was also recorded for experimental calculation purposes.
- The laser pointer was turned on, and moved to an angle such that multiple laser 'dots' could be seen.
- The distances between the laser 'dots' were measured and recorded.
Step 7: Discussion
The laser pointer dots were the patterns generated by the diffraction gratings of the CD. As light is behaving as a wave, it is constructing peak points of constructive interference. Areas without light are where there were destructive interference.
In addition, the noise of light which can be detected by the camera, but is difficult to see with the naked eye, is the result of the light interfering with other particles in the surrounding
Step 8: Results: Analysis of Data
- The distances between the 'dots' were approximately 41.9cm
- The distance between the CD and the wall is 42.0cm
- This height is 15.4 cm.
The distance between slits of the CD, i.e. gratings between tracks, was calculated using the formula: d (sinθ) = mλ. Using the given wavelength of the green laser beam provided by the safety label of the laser as 532nm, and the values collected from the experiment, the spacing between tracks for a CD was calculated to be 1.54 micrometer.
Step 9: Conclusion
This experiment has shown evidence that light behaves in a wave nature, producing peaks of constructive and destructive interference. However, does not provide any conclusion whether light can or cannot behave like a particle. The result of 1.54 micrometer is quite consistent with that of a CD, whose actual track spacing is 1.60 micrometer.