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# A single concept to explain everything in Ray Optics : Spherical Mirrors

In the last article, we introduced you the Fermat’s principle of least time for light rays and made the bold claim that we will be teaching the entire ray optics with just this single principle at the core. And till now, we have stuck to our promise. Using Fermat’s principle of least time we have been able to prove two wonderful 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 also put our claim to test: Teaching you about spherical mirrors with just the understanding you have built in the previous videos without the addition of any extra law or principle. So, are you ready??

We will begin by discussing what spherical mirrors are and how are they formed and then move on to describe important terminologies related to spherical mirrors like Centre of curvature, Pole, Radius of Curvature and Principal axis. Since all these concepts will be visually explained, you need not be afraid of getting stuck in the boring textbook loop.

Next, we will describe the properties of two important rays concerning spherical mirrors:

1. A ray passing through the centre of curvature retraces its path after 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.

So, thatâ€™s it for this article. But brace yourself for the next one because thatâ€™s where the actual fun begins. Using our understanding of the aforementioned two special rays, we will play with image formation by spherical mirrors and derive all the cases discussed in the book with ease and fun. So are you excited?? Send in your suggestions and doubts in the comment section below!

## Frequently Asked Questions on Spherical Mirrors

### When is Snellâ€™s law not valid?

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

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

The reflected ray will lie in the plane of incidence.

### 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 extent.

### 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.