Optics
Learn Optics with notes, examples, and practice questions.
Chapter Overview
Optics covers reflection, refraction, lenses, mirrors, wave optics — interference, diffraction, and polarisation. Ray optics for instruments; wave optics for nature of light.
Ray Optics
Mirror
1/f = 1/v + 1/u ; f = R/2
Lens
1/f = (n−1)(1/R₁−1/R₂)
Lens maker
1/f = 1/v − 1/u (sign convention)
Power
P = 1/f (dioptre)
Magnification
m = h'/h = v/u
Wave Optics
Young's double slit
β = λD/d (fringe width)
Condition
Path diff = nλ (bright); (n+½)λ (dark)
Brewster
tan i_p = n
Solved Examples
Step-by-step solutions — read each step before checking the final answer.
Mirror
u=−30cm, f=−15cm (concave).
- 11/v=1/f−1/u=−1/15+1/30
- 2v=−30cm real image
Answer
v=−30 cm, m=−1
Fringe width
λ=600nm, D=1m, d=0.2mm.
- 1β=λD/d=3mm
Answer
3 mm
Key Points to Remember
- ✓ New Cartesian sign convention
- ✓ Total internal reflection: n sin i > 1
- ✓ Resolving power of instruments
Exam Tips
- • Draw ray diagrams
- • Convert nm to m for λ
- • State formula before numbers
Formula Cheat Sheet
Quick reference — NCERT board exam formulas
Ray Optics
- Mirror:1/f = 1/v + 1/u ; f = R/2
- Lens:1/f = 1/v − 1/u
- Lens maker:1/f = (n−1)(1/R₁−1/R₂)
- Power:P = 1/f (dioptre)
- Magnification:m = h'/h = v/u
- Snell's law:n₁ sin i = n₂ sin r
Wave Optics
- Fringe width:β = λD/d
- Bright fringe:Path diff = nλ
- Dark fringe:Path diff = (n+½)λ
- Brewster angle:tan i_p = n
Practice MCQs — Optics
Test your understanding with topic-wise multiple choice questions. Explanations appear after each answer.
Power of lens P=