Wave Front Simplified Explanation

Wave Front

Definition: It is the locus of points in the same phase.

Let us take a beam of light. A beam of light doesn't consist of one wave of light but many as shown in the image.

In the second image, I have drawn points on the waves that are in the same phase(the crests). When we connect these dots, we get a straight line. This is the wave front of these waves.

There are 3 types of wave front:

1. Spherical wave front
2. Plane wave front
3. Cylindrical wave front

Spherical Wave Front

• Here, the shape of the wave front is a sphere, just like a football. 
• A spherical wave front is created when the source of waves is a point source, i,e, dimensionless.

For example, when we throw a stone in a lake, ripples are formed in all directions surrounding the point of impact. If we look from the top, it will look like concentric circles. If we join the points in the same phase, we obtain a circle. But this is only from the top. If we keep doing this from all the angles, we obtain a sphere. This is the spherical wave front. 

Just try to picturize a 3D image in your mind.

• A point. 
• Waves coming out of this point from all 3 axis's.
• Points in the same phase are represented as dots in all the waves.
• Connect these dots. You get a sphere! 

Plane Wave Front

A plane wave front is obtained when the source of waves is located at infinity.

When we says that the source of waves is at infinity, we mean that the waves of light are so almost parallel, that they are assumed parallel(actually they are diverging waves). 

A plane wave front looks like a sheet of paper. When we observe it from the front, it looks like a plane, whereas if we view it sideways, we see parallel lines.

Cylindrical Wave Front

A cylindrical wave front is obtained when the source of waves is a line source, i,e, it is like a lightsaber. 

A cylindrical wave front looks like a cylinder.

If we draw the wave front for one plane, we will obtain a concentric circle. But is we continue to draw the wave front of different planes,we will obtain more concentric circles which combine to form a cylinder.