Lenses

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A lens is a transparent medium in which each refracting surface is part of a sphere. Unlike a plain glass sheet, a lens can converge or diverge light rays due to its curved surfaces. A convex lens con

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Convex lens: Thicker in the middle, converges light rays, can form real images, principal focus is real. Concave lens: Thinner in the middle (thicker at edges), diverges light rays, forms only virtual

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Optic centre (O): Midpoint of the lens. Principal focus (F): Point where parallel rays converge (convex) or appear to diverge from (concave) after refraction. Focal length (f): Distance from optic cen

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Move the lens sideways while observing letters: With convex lens - letters appear to move in opposite direction. With concave lens - letters appear to move in same direction as the lens movement. This

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1) A ray parallel to optic axis passes through the principal focus after refraction. 2) A ray passing through optic centre goes straight without deviation. 3) A ray passing through the principal focus

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Position: Between F and 2F on the other side. Characteristics: Real, inverted, diminished (smaller than object). This configuration is used in cameras and human eye to form images of distant objects.

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Position: Same side as object, beyond the object. Characteristics: Virtual, erect, magnified (larger than object). This is the principle behind magnifying glasses and simple microscopes.

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The image is formed at infinity (very far away). The refracted rays are parallel and do not converge. Practically, a very large image is formed far from the lens. This principle is used in searchlight