1. Laws of Reflection of Light:

(i) Angle of incidence is equal to the angle of reflection.

(ii) Incident ray, reflected ray and the normal drawn to the reflecting surface at the point of incidence, lie in the same plane.

2. Laws of Refraction of Light:

(i) For a given pair of medium, and for given colour of light, the ratio between the sine of angle of incidence and sine of angle of refraction is constant and equal to relative refractive index of medium $2$ with respect to medium $1$ .

If $i$ is the angle of incidence and $r$ is the angle of refraction, then $\frac{\sin i}{\sin r} =$ constant.

(ii) Incident ray, refracted ray, normal drawn to the interface, at the point of incidence, lie in the same plane.

3. Spherical Mirrors:

(i) A mirror that is polished from the outer side of a hollow sphere, such that the reflecting side is towards the hollow side, is called a concave mirror.

(ii) A mirror that is polished from the hollow side of the sphere, such that the reflecting surface is towards the bulging side, is called a convex mirror.

(iii) The focal length $(f)$ of a spherical mirror is half of the radius of curvature $(R)$ . $f = \frac{R}{2}$

(iv) The mirror formula for spherical mirrors is $\frac{1}{v} + \frac{1}{u} = \frac{1}{f}$ and gives the relationship between object distance $u$ , image distance $v$ and the focal length $f$ .

(v) The magnification produced by a spherical mirror, $m = - \frac{v}{u}$ .

4. New Cartesian Sign Conventions:

In this convention, the pole $(P)$ of the mirror is taken as the origin. The principal axis of the mirror is taken as the x-axis of the coordinate system. The conventions are as follows –

(i) The object is always placed to the left of the mirror. This implies that the light from the object falls on the mirror from the left-hand side.

(ii) All distances parallel to the principal axis are measured from the pole of the mirror.

(iii) All the distances measured to the right of the origin (along $+$ $x$ -axis) are taken as positive while those measured to the left of the origin (along $-$ $x$ -axis) are taken as negative.

(iv) Distances measured perpendicular to and above the principal axis (along $+$ $y$ -axis) are taken as positive.

(v) Distances measured perpendicular to and below the principal axis (along $-$ $y$ -axis) are taken as negative.

5. Refraction of Light:

(i) The phenomenon due to which a ray of light deviates from its path at the separation of two media, when the ray of light is travelling from one optical medium to another optical medium is called refraction of light.

(ii) The rays of light while travelling from rarer to denser medium bend towards the normal drawn at the point of incidence. The rays travelling from a denser to a rarer medium, bend away from the normal.

(iii) Refractive index of a medium, $μ = \frac{Speed of light in vacuum}{Speed of light in the medium}$ .

(iv) Relative refractive index of medium $2$ with respect to medium $1$ , $μ_{2,1} = \frac{Speed of light in medium 1}{Speed of light in medium 2}$ .

(v) In a rectangular glass slab, when light is passing through two opposite faces, angle of incidence is always equal to that angle of the emergence.

6. Refraction by Spherical Lenses:

(i) Lens formula for spherical lens is $\frac{1}{v} - \frac{1}{u} = \frac{1}{f}$ and gives relationship between object distance $u$ , image distance $v$ and the focal length $f$ .

(ii) Magnification produced by a lens, $m = \frac{v}{u}$ .

(iii) Power of lens $(P)$ is the reciprocal of its focal length $(f)$ in metre. The SI unit of power of a lens is dioptre ( $D$ ). $P = \frac{1}{f (in metre)}$ .

The correct sequencing of angle of incidence, angle of emergence, angle of refraction and lateral displacement shown in the following diagram by digits 1, 2, 3 and 4 is:

Important Questions on Reflection and Refraction

Learn and Prepare for any exam you want !

The correct sequencing of angle of incidence, angle of emergence, angle of refraction and lateral displacement shown in the following diagram by digits $1$ , $+$ , $y$ and $4$ is: