What are Ray Optics and Optical Instruments?
Ray Optics and Optical Instruments explores how light travels in straight lines and interacts with mirrors, lenses, and prisms. Students of Class 12 Physics study this to understand image formation, reflection, refraction, and devices like microscopes and telescopes. This topic is crucial for both CBSE board exams and competitive exams like NEET and JEE.
Ray Optics and Optical Instruments
Ray Optics (Geometrical Optics) assumes light travels in straight lines. When it meets a boundary between two media, it either reflects back or bends (refracts). The study includes plane and spherical mirrors, refraction at curved surfaces, lenses, and optical devices.
- Reflection: Bouncing back of light from a smooth surface.
- Refraction: Change in the direction of light when it passes from one medium to another.
- Total Internal Reflection (TIR): When light reflects completely within a denser medium instead of refracting out.
Laws of Reflection and Refraction
| Law | Equation | Explanation |
|---|---|---|
| Law of Reflection | ∠i = ∠r | Angle of incidence equals angle of reflection. |
| Snell’s Law | \( n_1\sin i = n_2\sin r \) | Defines the refractive index between two media. |
| Mirror Formula | \( \frac{1}{f} = \frac{1}{v} + \frac{1}{u} \) | Relates focal length, image distance, and object distance. |
| Lens Formula | \( \frac{1}{f} = \frac{1}{v} – \frac{1}{u} \) | Used for convex and concave lenses. |
Important Formulas
\( m = \frac{h_i}{h_o} = \frac{v}{u} \) — Magnification Formula
\( n = \frac{\sin i}{\sin r} = \frac{v_1}{v_2} \) — Refractive Index Formula
Applications and Examples
- Periscope: Uses plane mirrors for viewing over obstacles.
- Optical Fibre: Uses TIR to transmit light signals with minimal loss.
- Microscope: Uses two convex lenses to magnify tiny objects.
- Telescope: Uses lenses or mirrors to view distant objects.