# 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.

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.

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

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: