CBSE · Class 10 · Physics · Chapter 10

Human Eye and Colourful World — Formula Sheet

Board Formulas

8 formulas

1.Power of Accommodation
$P = \frac{1}{f}$
Ability of the eye lens to change focal length via ciliary muscles. Range: about 2 D for a normal adult eye.
2.Least Distance of Distinct Vision
$D = 25 cm$
For a normal adult eye, the near point is 25 cm from the eye. Far point = infinity.
3.Focal Length for Myopia Correction★
$f = - x (far point at distance x)$
Use a concave lens whose focal length equals the (negative of) far point. Then image of infinity forms at the far point.
4.Focal Length for Hypermetropia Correction★
$f = \frac{D \cdot y}{y - D}$
y = defective near point (>25 cm), D = 25 cm. Formula gives positive f ⇒ convex lens.
5.Power of Lens (Dioptres)
$P = \frac{1}{f (in metres)}$
Concave lens ⇒ negative P (for myopia). Convex lens ⇒ positive P (for hypermetropia).
6.Angle of Deviation in a Prism
$δ = (i_{1} + i_{2}) - A$
A = angle of prism. Minimum deviation occurs when i₁ = i₂ (symmetric passage).
7.Rayleigh Scattering Intensity
$I \propto \frac{1}{λ ^{4}}$
Shorter wavelengths (blue) scatter much more than longer (red). Explains blue sky and red Sun at sunset.
8.Snell's Law at Prism Faces
$n = \frac{s i n i}{s i n r}$
Applied at both refracting surfaces of the prism. Wavelength-dependent n causes dispersion.