Why does a diamond sparkle so brightly?

Diamond has a very high refractive index (~2.42), giving a very small critical angle (~24°). Most light rays striking the many facets of a cut diamond exceed this critical angle, causing total internal reflection multiple times before exiting. This repeated TIR concentrates the light and produces brilliant sparkle.

What is the difference between real and virtual images?

A real image is formed when reflected/refracted rays actually meet at a point. It can be projected on a screen, is always inverted, and is formed on the same side as the observer (mirrors) or opposite side (lenses). A virtual image is formed where rays appear to diverge from; it cannot be projected on a screen, is always erect, and is formed on the same side as the object (lenses).

How does an optical fibre work?

An optical fibre uses total internal reflection to transmit light. The core has a higher refractive index than the cladding. Light entering at less than the acceptance angle undergoes repeated TIR along the fibre without energy loss. This allows signals to travel very long distances with minimal attenuation. Applications: internet cables, medical endoscopes, decorative lamps.

Reflection, Refraction, and Mirror/Lens Formula

Ray Optics and Optical Instruments • Class 12 Physics • NCERT • CBSE

Mirror formula: 1/f = 1/v + 1/u. Lens formula: 1/f = 1/v − 1/u. Snell's Law: n₁ sinθ₁ = n₂ sinθ₂. Total internal reflection occurs when angle of incidence > critical angle (sinC = 1/n).

Key Formulas

Mirror formula: 1/f = 1/v + 1/u
Lens formula: 1/f = 1/v − 1/u
Snell's Law: n₁ sinθ₁ = n₂ sinθ₂
Critical angle: sinC = 1/n
Lens Maker's: 1/f = (n−1)[1/R₁ − 1/R₂]
Power: P = 1/f (Dioptre)

Frequently Asked Questions

Why does a diamond sparkle so brightly?: Diamond has a very high refractive index (~2.42), giving a very small critical angle (~24°). Most light rays striking the many facets of a cut diamond exceed this critical angle, causing total internal reflection multiple times before exiting. This repeated TIR concentrates the light and produces brilliant sparkle.
What is the difference between real and virtual images?: A real image is formed when reflected/refracted rays actually meet at a point. It can be projected on a screen, is always inverted, and is formed on the same side as the observer (mirrors) or opposite side (lenses). A virtual image is formed where rays appear to diverge from; it cannot be projected on a screen, is always erect, and is formed on the same side as the object (lenses).
How does an optical fibre work?: An optical fibre uses total internal reflection to transmit light. The core has a higher refractive index than the cladding. Light entering at less than the acceptance angle undergoes repeated TIR along the fibre without energy loss. This allows signals to travel very long distances with minimal attenuation. Applications: internet cables, medical endoscopes, decorative lamps.

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