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#optical lenses

3 public questions tagged with this topic.

Refraction at Spherical Surfaces and Lens Maker's Formula

In a concave lens, why is the image always formed on the same side as the object?

**Spherical refracting surface** power P = (n₂-n₁)/R, lens power sum of two surfaces. Lens maker derivation combines two refractions, sign of R₂ negative for second surface convex opposite direction, yielding 1/f positive for convex lens. A concave lens diverges light rays, making them appear to originate from a point on the same side as the object when traced backward. This results in a virtual image that cannot be projected on a screen, always forming on the object’s side regardless of its position. Substituting values gives Because rays diverge and appear to come from the same side, which m

Ref: NCERT > Physics Book > Ray Optics > Refraction at Spherical Surfaces and Lens Maker's Formula

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Optical Instruments - Simple and Compound Microscope

In a compound microscope, why is the final image inverted with respect to the object?

**Microscope principle** objective of short focal length forms real image between F_e and 2F_e of eyepiece, eyepiece magnifies to virtual image at D, total magnification product, for f_o=2 cm, f_e=5 cm, L=20 cm, m_o≈10, M_e≈6, M≈60, illustrating high magnification from two stages. In a compound microscope, the objective lens forms a real, inverted image of the object. The eyepiece then acts as a magnifying lens, forming a virtual image of this inverted intermediate image. Since the eyepiece does not reinvert the image, the final image remains inverted relative to the original object. Substitut

Ref: NCERT > Physics Book > Ray Optics > Optical Instruments - Simple and Compound Microscope

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Refraction at Spherical Surfaces and Lens Maker's Formula

A double convex lens of refractive index \( 1.6 \) has radii of curvature \( 25 \, \text{cm} \) and \( -25 \, \text{cm}

**Lens maker's formula** 1/f = (n-1)(1/R₁ - 1/R₂), n refractive index, R₁,R₂ radii of curvature (m), sign convention R positive if surface convex towards incident light. For double convex R₁=12 cm, R₂=-12 cm, n=1.5, 1/f=(0.5)(1/12 -1/(-12))=(0.5)(2/12)=1/12, f=12 cm, converging. Lens maker’s formula: (1/f) = (n - 1) ( (1/R₁) - (1/R₂) ) . n = 1.6 , R₁ = 25 cm , R₂ = -25 cm . (1/f) = (1.6 - 1) ( (1/25) - (1/-25) ) = 0.6 ( (1/25) + (1/25) ) = 0.6 × (2/25) = (1.2/25) . f = (25/1.2) ≈ 20.83 cm . Substituting values gives 20.8 cm, which matches

Ref: NCERT > Physics Book > Ray Optics > Refraction at Spherical Surfaces and Lens Maker's Formula

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