Diffraction vs. interference

Imagine you are playing with water waves in a pool. If you put a rock in the water and make some waves, you will see that the waves spread out in all directions from the rock. This is called diffraction.

Now, let's say you have two rocks in the water and you make waves again. When the waves from one rock meet the waves from the other rock, they combine and make some bigger waves. This is called interference.

Similarly, when light waves pass through narrow gaps or slits, they also spread out in all directions and this is called diffraction. But when two light waves from different sources meet each other, they can either add up or cancel out each other, and this is called interference.

So, diffraction is when waves spread out from a single source, while interference is when waves add up or cancel out when they meet from different sources.