PHY C15: Diffraction

Now we’re going to cover:

  • Diffraction (basics)
  • Huygens’ Principle
  • Factors affecting Diffraction

Let’s jump in!

What is Diffraction?
The spreading of a wave after passing through a narrow slit or past an edge.

Image result for diffraction gif
Image result for diffraction edge gif

What is the effect of diffraction?
Waves can reach regions where they would not be seen if they travelled in straight lines.


Why does diffraction occur?
One way of explaining diffraction is by Huygens’ principle of diffraction.

According Huygens, every point on a wavefront at any moment in time can be thought of as a source of new waves.

The infinitely tiny waves are called WAVELETS.

Image result for huygens principle gif
Image result for huygens principle plane wave gif
From Britannica

Here’s a few examples to get accustomed to the idea:

Plane wave 
Circular wave Image result for huygens principle circular wavegif
Reflection/RefractionImage result for huygens principle gif 
Diffraction through a slit 
From http://spiff.rit.edu/classes/phys283/lectures/huygens/huygens.html & https://www.askiitians.com/iit-jee-wave-optics/wave-nature-of-light/

As you can see, the reason behind diffraction is that the presence of a wall blocks the wavelets just behind them. Thus, the wavelets spread out in a circular pattern around the edge.


What affects the amount of diffraction?

  • Wavelength, λ
  • Width of gap

The smaller the width of the gap compared to λ, the larger the effect of diffraction.

However, less energy is also allowed past the slit if its width is smaller – resulting in a wave of less intensity.

If the gap is too small, the wave may not even be noticeable.

As a result, the effect of diffraction is the largest when the width of the gap is roughly λ.


Extra Resources:

https://phet.colorado.edu/en/simulation/wave-interference

Next, we’ll look at some less-intuitive effects in diffraction.

⇐ Previous in Physics: Double Slit Interference
⇒ Next in Physics: Single-slit interference

3 thoughts on “PHY C15: Diffraction

  1. Pingback: PHY C15: Double Slit Interference – ProDuckThieves

  2. Pingback: PHY C15: Single-Slit Interference – ProDuckThieves

  3. Pingback: Huygens' Principle | AtomsTalk

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