Wave Optics Lab Report: Comparing Coherent and Incoherent Light Sources, Papers of Physics

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Lab Report

Experiment 3:

Wave Optics

Name: Maris Quagliata Lab Partner:Bashkar Coarse/Section/Lab Number: PHY208/ GH2/ Lab 3 Date: 3/19/ TA Name:Raihan Uddin

I. Introduction

In this lab, the students aim to learn the wave nature of light and look deeper into the interference effects. Light, as we know it, behaves similarly to waves, displaying phenomena like interference and diffraction. This happens because of the principle of superposition, where waves combine their strengths - sometimes making bigger waves, sometimes canceling each other out. It's important to know that there are two main types of light sources: coherent and incoherent. Coherent sources give off waves that are all in sync, like a laser pointer. Incoherent sources give off waves that are all over the place, like a regular light bulb. By doing experiments in this lab, the students want to compare these types of light sources, see how light moves through holes and slits, and figure out things like the wavelength of light by looking at interference patterns.

II. Procedure

In this lab, students were asked to first check to make sure all equipment was accounted for, this included:

1. One optics track
2. One Screen with holder
3. One slide holder
4. Two slides with slits
5. One laser source
6. One incandescent source
7. One index card
8. One pair of scissors
9. One Digital Caliper
10. One Ruler Students went over their understanding of interference of light and how the principles of superposition apply. Part I: The first experiment was to examine regular, non-coherent white light through an aperture. Students were asked to make their own out of paper by cutting a 2-3 millimeter wide slit in an index card. Students placed the index card with the slit next to the incandescent light source and the screen about 20cm apart from the opening. The imagewe saw can be seen below, along with the sketch of the intensity profile using what was seen.

No, the wider the slit, the wider the intensity profile. Are the edges of the intensity profiles sharp? or smooth? For the incandescent light source the edges are sharp endings, for the laser they are smoother. Explain the difference between monochromatic and polychromatic light. Give examples of each kind. Why are interference effects harder to observe with polychromatic light? Describe how you could create a monochromatic light source using polychromatic rays from the sun? Monochromatic light, which is characterized by a single wavelength or color, is commonly generated by sources such as laser beams, gas discharge lamps, or light that has been meticulously filtered. Its interference patterns are sharply defined due to consistent frequency and phase relationships among its waves, resulting in easily discernible interference patterns. Conversely, polychromatic light, found in natural sources like sunlight or artificial sources such as LED bulbs, encompasses a spectrum of wavelengths, posing challenges in interference observations because of the varied phase relationships, leading to complex, overlapping patterns. To engineer a monochromatic light source from sunlight, one can employ techniques like a monochromator or interference filters to isolate a specific wavelength, ensuring meticulous control for experiments like interference studies. In your own words: explain the difference between coherent and incoherent sources? Do some research and find some examples of coherent and incoherent wave sources. Coherent sources emit waves with synchronized peaks and troughs, enabling the formation of distinct interference patterns, as seen in lasers. Incoherent sources, like ordinary light bulbs or sunlight, emit waves with random phase relationships, leading to less stable and less pronounced interference patterns. This difference is similar to a synchronized clap creating a clear sound (coherent) versus an unsynchronized clap resulting in overlapping noises (incoherent). Derive the formula that relates the wavelength of the light to the interference pattern fringe spacing. Show your work with algebra and geometry. Include a picture of your interference pattern as it appears on the screen. Provide an estimate using the measurements you obtained for the wavelength of the laser light. Finding 𝛳 Ym = 0.9cm = 9.0mm L=90.0cm=900.0mm 900.mm =9.0mm*tan𝛳 = arctan(9.0mm/900.0mm) = 0.5729386976834° or 0.57° Finding Δr sin𝛳 ≈ tan𝛳 d=0.25mm Δr/d=sin𝛳 = Δr/d = sin(0.57°)(0.25mm) = Δr = 0.0020966mm or 2096.6 nm

Finding λ for m=4 and m= m=4 & Ym = 9.0mm λ = ym L

×

d m

9.0 mm 900.0 mm

×

=0.000625∨625.00 nm m=8 & Ym = 18.15mm λ = ym L

×

d m

18.15 mm 900.0 mm

×

=0.000630∨630.21 nm

III. Conclusion

Through our experiment, we discovered that the wavelengths we measured were 625.0 nm and 630.21nm. However, the established wavelength of the laser beam is 650 nm, suggesting that our measurements were impacted by slight human error, leading to a somewhat noticeable disparity. This underscores the inherent limitations in the precision of our measurements. Additionally, we encountered difficulties in accurately gauging light distances and managing interference, particularly due to the diminutive size of their projections on the screen. It seems that integrating simulations and harnessing computer-based calculations could offer a more sophisticated method to attain precise data for this experiment, effectively bypassing the challenges associated with human observation and measurement constraints.