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# A Single Concept to Explain Everything in Ray Optics: Spherical Mirrors

In the last article, we introduced you to Fermat’s principle of least time for light rays to learn the entire ray optics at the core. Using Fermat’s principle of least time, we have been able to prove two laws: rectilinear propagation of light and laws of reflection.

In this article, we are going to move a step further and introduce you to spherical mirrors.

We will begin by discussing what spherical mirrors are and how they are formed and then move on to describe important terminologies related to spherical mirrors, like the centre of curvature, pole, the radius of curvature and principal axis. Here, we will be explaining these concepts visually to grasp them better.

Below, we have described the properties of two important rays related to spherical mirrors.

1. A ray passing through the centre of curvature retraces its path after the reflection from the mirror.
2. A ray parallel to the principal axis passes through a special point called the focus of the spherical mirror after reflection.

Using your understanding of the aforementioned two special rays, we will learn more about image formation by spherical mirrors and derive all the cases discussed in the book with easy-to-understand explanations. You can share your suggestions and doubts in the comment section below.

## Frequently Asked Questions on Spherical Mirrors

Q1

### When is Snellâ€™s law not valid?

Snellâ€™s law is not valid for normal incidence.

Q2

### When the light gets reflected, in which plane does the reflected ray lie?

The reflected ray will lie in the plane of incidence.

Q3

### What happens when a ray of white light is incident on the prism?

The incident light is dispersed into its constituent colours, and different colours deviate to a different extents.

Q4

### Why is the lens makerâ€™s formula called so?

The lens makerâ€™s formula is called so because it helps one to manufacture lenses of the required focal length from the glass of known refractive index.