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#lens optics

3 public questions tagged with this topic.

Wave Properties, Frequency and Energy Conservation

What property of light ensures that the time taken from an object point to its image point is the same along any ray pat

**Intensity not depend on speed** when enters denser medium because intensity I ∝ n E₀²? Actually Poynting vector S = E×H, energy density u =½ ε E², for same amplitude E₀ intensity proportional to n, but amplitude changes at interface due to reflection, total energy conserved incident = reflected + transmitted, interference does not destroy energy, it redistributes. The principle that light travels such that the optical path length (or time) is equal along all rays explains this, as the slower speed in a denser medium balances the shorter path. Using Δ = d sinθ, y = n λ D/d, a sinθ = n λ,

Ref: NCERT > Physics Book > Wave Optics > Wave Properties, Frequency and Energy Conservation

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Combination of Lenses and Lens Systems

In a concave lens, what is the effect on the image if the object is moved closer to the lens from a distant position?

**Two lenses in contact** behave as single lens with power sum, magnification product m = m₁×m₂. For f₁=20 cm (P₁=5 D), f₂=-20 cm (P₂=-5 D) in contact, P=0, F infinite, afocal system, beam emerges parallel, principle of corrective lenses for myopia/hypermetropia. For a concave lens, the image is always virtual, erect, and diminished. As the object moves closer, the image size increases (though still smaller than the object), and the image moves closer to the lens, but remains on the same side as the object. Substituting values gives Image size increases but remains diminished, which matches ex

Ref: NCERT > Physics Book > Ray Optics > Combination of Lenses and Lens Systems

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