Wave fronts on convex lenses help us identify the focal length of the lens which identifies the power of it too using P = 1/F. Wave fronts on lenses are more easily described through the use of diagrams. As you can see from this diagram, the focal length is the focus at which the light waves are coming in parallel to each other. Wave fronts are at tangents to the light waves. This topic needs to be known at Physics AS level.
Here is a diagram of what wave fronts are:
As you can see, wave fronts are always at a 90 degree angle to the light wave they are intersecting. Remembering that 1/V = 1/U + 1/F
, we see that the wave fronts at U
(left hand side of the diagram or object distance) have a curvature of 0. This is because 1/U = 1/ infinity which equals 0
(the light waves are parallel making the object distance at infinity). If me talking about U, V and F seems alien to you, I suggest you take a look at this article
which explains them clearly.
The lens adds curvature which we can work out as 1/F.
The curvature after the lens is 1/V. This gives us the equation…
Curvature after = curvature before + curvature added by lens
1/V = 1/U + 1/F