Mirage, sparkling of diamond twinkling of stars are some of the events taken place in nature.

When the angle of incidence exceeds the value of critical angle, the refracted ray is not possible, since r > 90° the ray is totally reflected back to the same medium. This is called as total internal reflection.

Glass has higher refractive index.

No unit for refractive index.

The spherical mirror equation is \(\frac { 1 }{ f } =\frac { 1 }{ { u } } +\frac { 1 }{ v } \)
u = distance of object.
v = distance of image.
f = focal length of spherical mirror.

Magnification is defined as the ratio of the height of the image \(\left( { h }_{ i } \right) \) to the height of object \(\left( { h }_{ 0 } \right) \)
Magnification \(=\frac { { h }_{ i } }{ { h }_{ 0 } }\)
1. Real image is negative sign.
2. Virtual image is positive sign
 

A ray of light going towards the centre of curvature is reflected back along the same path. It is a rule for construction of image formed by spherical mirrors.

(a)

b) Nature of the image is Real, inverted, magnified.

Height of object h₁ = 2 cm
Height of real image h₂ = -3 cm
Magnification   m =\(\frac { { h }_{ 2 } }{ { h }_{ 1 } } \)
= \(\frac { -3 }{ 2 } \)
= -1.5
We know that,  m = \(\frac { -v }{ u } \)
here, object distance u = - 16 cm 
Substituting the value, we get
 -1.5 = - \(\frac { v }{ (-16) } \)
-1.5 =  \(\frac { v }{ (-16) } \)
v = 16 \(\times\) -1.5
v = -24 cm
The position of image is 24 cm in front of the mirror (negative sign indicates that the image is on the left side of the mirror).