Difference Between Diffraction and Interference

The key difference between diffraction and interference is that diffraction is the bending of wavefronts in the presence of sharp edges, whereas interference is the property of making a net effect using multiple waves.

Both diffraction and interference are properties of waves we discuss under waves and vibrations in physics. Diffraction is the bending of waves in the presence of sharp edges, whereas interference is the effect of more than one wave at a point on a given time. Both of these phenomena are very important in the understanding of waves and in physics in general.

CONTENTS

1. Overview and Key Difference
2. What is Diffraction 
3. What is Interference
4. Side by Side Comparison – Diffraction vs Interference in Tabular Form
5. Summary

What is Diffraction?

Diffraction is a phenomenon observed in waves. Diffraction refers to various behaviours of waves when they meet an obstacle. This phenomenon is described as the apparent bending of waves around small obstacles and the spreading out of waves past small openings. We can easily observe this using a ripple tank or a similar setup. Here, the waves generated on the water is useful to study the effects of diffraction when a small object or a small hole is present.

The amount of diffraction depends on the size of the hole (slit) and the wavelength of the wave. If we are to observe diffraction, the width of the slit and the wavelength of the wave must be of the same order or nearly equal. If the wavelength is much larger or much smaller than the width of the slit, an observable amount of diffraction does not form.

Diffraction of light through a small slit is evidence for the wave nature of light. Some of the most famous experiments in diffraction are Young’s single slit experiment and Young’s double slit experiment. The diffraction grating is one of the most useful products based on the theory of diffraction. It is useful to obtain high-resolution spectra.

What is Interference?

Interference is the phenomenon where two or more waves superimpose to make a resulting motion at a given point in space. We discuss this phenomenon regarding coherent waves. This is because, for coherent waves, we can explain the interference pattern mathematically in a simple way. When two waves of the same amplitude interfere with each other, the resulting amplitude at the interfering point can vary from zero to twice the amplitude.

The main principle behind describing interference is the principle of superimposition. Interference is observable with every form of waves. It is also a wave property. Interference of two waves can occur as either constructive or destructive interference; here, both waves are of the same type and act on the same point in space.

What is the Difference Between Diffraction and Interference?

Diffraction is a phenomenon observed in waves. Interference, on the other hand, is the phenomenon where two or more waves superimpose to make a resulting motion at a given point in space. The key difference between diffraction and interference is that diffraction is the bending of wavefronts in the presence of sharp edges, whereas interference is the property of making a net effect using multiple waves. Moreover, diffraction requires an obstacle, while interference doesn’t. Furthermore, the path of the incident wave changes due to diffraction, but it stays intact for interference.

Summary – Diffraction vs Interference

Diffraction is a phenomenon observed in waves while interference is the phenomenon where two or more waves superimpose to make a resulting motion at a given point in space. The key difference between diffraction and interference is that diffraction is the bending of wavefronts in the presence of sharp edges, whereas interference is the property of making a net effect using multiple waves.

Reference:

1. Jones, Andrew Zimmerman. “Interference, Diffraction & the Principle of Superposition.” ThoughtCo, Jan. 31, 2019, Available here.

Image Courtesy:

1. “One wave slit diffraction dirichlet bw” By L3erdnik – Own work (CC0) via Commons Wikimedia
2. “Interference of two waves” By Haade – Copied en wiki used in interference article (CC BY-SA 3.0) via Commons Wikimedia