Question

what are the laws of reflection & refraction?? what is refractive index???

Answer 1

Jump to Total internal reflection and critical angle · Snell's law (also known as Snell–Descartes law and the law of refraction) is a formula used to describe the relationship between the angles of incidence and refraction, when referring to light or other waves passing through a boundary between two different isotropic media, such as water, glass, or air.
History
Explanation
Derivations and formula

Answer 2

laws of reflection states that
the angle of incidence is equal to the angle of reflection
the incident ray reflected ray and normal at the point of incidence all lie on the same plane
law of refraction states
the ratio of sine of angle of incidence to the sine of angle of refraction is constant for a given pair of media(snells law)
the incident ray refracted ray and normal at the point of incidence all lie on Same plane

refractive index expressed as mu
it is the ratio of sine of angle of incidence to the sine of angle of refraction
it can be used to find real and apparent depth