Here's why:

* Spherical waves originate from a point source. Imagine dropping a pebble into a still pond. The ripples spread out in circles from the point of impact, creating a two-dimensional wave pattern.

* In three dimensions, the wave pattern expands outward as a sphere. This is why sound waves from a speaker and light waves from a light bulb travel outward in all directions.

Let me know if you have any other questions!