Optics is the branch of physics that tells how the light behaves, its properties and its interactions. There are many formulas in optics. Some of them are,

Refractive index,
n = $\frac{Speed \ of \ light \ in \ vacuum}{Speed \ of \ light \ in \ a \ medium}$ = $\frac{c}{v}$

Snell's law of refraction: If n1 and n2 are the refractive indexes of medium 1 and medium 2 and $\theta_1$ is the angle of the incident ray and $\theta_2 is the angle of refracted ray. The snell's law is given by, n1 sin$\theta_1$= n2 sin$\theta_2$. The critical angle is given by, sin$\theta_c$=$\frac{n_1}{n_2}$. Mirror formula,$\frac{1}{u}$+$\frac{1}{v}$=$\frac{1}{f}$. Where, u is image distance, v is the object distance, f is the focal length. Magnification, m =$\frac{v}{u}$=$\frac{v-f}{f}$=$\frac{f}{u-f}$, or m =$\frac{I}{O}$. Thin lens formula,$\frac{1}{f}$=$\frac{1}{v} - \frac{1}{u}$Where, u is image distance, v is object distance. The power of lens is given by, P =$\frac{1}{Focal\ length}$. The equivalent focal length of two lens in contact is given by,$\frac{1}{F}$=$\frac{1}{f_1} + \frac{1}{f_2}$. Where, f1 is the focal length of the lens 1, f2 is the focal length of the lens 2, F is equivalent focal length.. ## Optics Solved Problems Below are given some examples on optics, you can go through: Question 1: The light rays travels from air to water at an incidence angle of 420. Calculate its reflection angle. Solution: Given: R.I in air n1 = 1, R.I in water n2 = 1.33, angle of incidence$\theta_1$= 420 The snell's law formula is given by : n1 sin$\theta_1$= n2 sin$\theta_2$The angle of reflection$\theta_2$is given by, Sin$\theta_2$=$\frac{n_1 sin \theta_1}{n_2}$Sin$\theta_2$=$\frac{1 \times sin 42^0}{1.33}$Sin$\theta_2$= 0.503 Therefore, reflection angle,$\theta_2$is 30.2$^{\circ}$. Question 2: The light has a speed in glass as 2.32$\times$108 m/s.Calculate the refractive index of glass. Solution: Given: Speed of light in glass v = 2.32$\times$108 m/s, Speed of light in vacuum = 3$\times$108 m/s The refractive index n is given by, Refractive index, n =$\frac{Speed \ of \ light \ in \ vacuum}{Speed \ of \ light \ in \ a \ medium}$n =$\frac{c}{v}$n =$\frac{3 \times 10^8 m/s}{2.32 \times 10^8 m/s}\$

n = 1.29.

Therefore, refractive index of glass is 1.29.