Double Slit Diffraction
As we learned in the previous lesson, light was widely considered to be composed of particles—or "corpuscles"—at the start of the 19th century. This view was strongly supported by the scientific community, largely due to the enduring authority of Isaac Newton.
However, a pivotal experiment in the early 1800s dealt a severe blow to the corpuscular model.
Thomas Young designed an experiment to test the wave nature of light. What is now known as Young’s double-slit experiment provided compelling, empirical evidence that light behaves as a wave.
This lesson reviews the phenomena of diffraction and interference, demonstrating how they explain double-slit interference patterns to support the wave model of light. We will also examine the underlying mathematical models and explore how diffraction gratings allow for precise quantitative analysis of light.
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This video provide a quick summary of the double slit experiment.
Otherwise, continue on...
Young's Double Slit Experiment
This video examines the basis of this experiment including a mathematical analysis for the behaviour.
Its now time for you to see the effect through this interactive (by Tom Walsh)
The dots align exactly when this takes place
Alter any of the sliders and see the effect of the superposition of the two waves.
It is important to appreciate the mathematical formula of mλ = dsinθ , that only certain combinations of Y, d, L and λ will result in constructive interference.
You can do this by adjusting the various variables to generate constructive interference at the screen.
Below is a sample problem with a video that explain how to solve it. It is suggested you try the problem beforehand, as this actually aids understanding, even if you are unsure if you are correct.
Use the animation below to practise various scenarios.
Diffraction Gratings
The result is much more defined diffraction patterns which increases the precision of the measurements.
This video discusses the physics principles behind the diffraction with some examples.
We can now explore the formula mλ = dsinθ further. The animation lets you explore the effect of grating, wavelength and distance to the maxima separation. (by Tom Walsh)
A good way to use this is to
- Set two variables yourself
- Measure the distance between the maxima
- Calculate the value for the remaining variable and compare it to the animation.