Maharashtra State Board · Class 10 · Physics · Chapter 6

Refraction of Light — Formula Sheet

Board Formulas

9 formulas

1.Laws of Reflection★
$∠ i = ∠ r$
Angle of incidence = angle of reflection. Both measured from the normal.
2.Mirror Formula★
$\frac{1}{v} + \frac{1}{u} = \frac{1}{f}$
u = object distance, v = image distance, f = focal length. Use sign convention.
3.Magnification (Mirror)
$m = \frac{h ^{'}}{h} = - \frac{v}{u}$
Negative m ⇒ inverted (real); positive ⇒ upright (virtual).
4.Focal Length and Radius of Curvature
$f = \frac{R}{2}$
For spherical mirrors, focal length is half the radius of curvature.
5.Snell's Law★
$n_{21} = \frac{s i n i}{s i n r} = \frac{n _{2}}{n _{1}}$
Refractive index of medium 2 with respect to medium 1.
6.Absolute Refractive Index
$n = \frac{c}{v}$
$c$ : Speed of light in vacuum ≈ 3×10⁸ m/s · $v$ : Speed of light in the medium (m/s)
Ratio of speed of light in vacuum to speed in the medium. Always ≥ 1.
7.Lens Formula
$\frac{1}{v} - \frac{1}{u} = \frac{1}{f}$
Note the MINUS sign (unlike mirror formula). Applies to thin lenses.
8.Power of a Lens
$P = \frac{1}{f ( in m )}$
Unit: dioptre (D). Convex lens ⇒ +P, concave lens ⇒ −P.
9.Magnification (Lens)
$m = \frac{h ^{'}}{h} = \frac{v}{u}$
Positive for erect (virtual), negative for inverted (real).