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Lenses A transparent object used to change the path of light Examples: Human eye Eye glasses Camera Microscope Telescope Reading stones used by monks, nuns, and scholars ~1000 C.E.

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Lenses THERE ARE ALWAYS TWO REFRACTIONS IN A LENS

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Lenses Two basic shapes Converging lens Diverging lens

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Converging Lens A lens that has its thickest part in the middle Causes all incident parallel rays to converge at a single point after refraction

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Converging Lens OPTICAL CENTRE: the exact centre of the lens

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Ray diagrams for Converging Lenses

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Images through Converging Lenses Lets practice

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Images in Convex lens vu f Image Real, inverted & highly diminished Image formed in convex lens when the object is placed at infinity FF 2F Use As a camera lens when object is very far, burning lens

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object Images in Convex lens vu f Image Real, inverted & diminished Image formed in convex lens when the object is placed beyond 2f FF 2F Use As a camera lens when object is not very far

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Image formed in convex lens when the object is placed at 2f object Image Real, inverted & same size as object Images in Convex lens vu f FF 2F Use In terrestrial telescope for erecting the image

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Image formed in convex lens when the object is placed between f and 2f object Image Real, inverted & magnified Images in Convex lens vu f FF 2F Use Cinema and slide projectors

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Image formed in convex lens when the object is placed at the focus object Image At Infinity, inverted and highly magnified Images in Convex lens u f FF 2F Use In collimator of a spectrometer to obtain parallel beam

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Image formed in convex lens when the object is placed between the Focus and optical centre object Images in Convex lens u f Image Virtual, magnified & upright FF 2F Use As a reading glass

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Converging Lenses Can produce real and virtual images The size and attitude will vary depending on the location of the object Many uses including to correct for far-sightedness LocationSizeAttitudeLocationType Beyond 2F SmallerInvertedBehindReal At 2F SameInvertedBehindReal Between 2F and F LargerinvertedBehindReal At F No clear image Inside F largeruprightIn frontVirtual Object Image -------------------------------------------- ---

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Diverging Lens A lens that has its thinnest part in the middle Causes all incident parallel light rays to spread apart after refraction

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Diverging Lens

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Ray diagrams for Diverging Lenses

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Images through Diverging Lenses Lets practice

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Diverging Lenses Only produce virtual images that are always smaller, upright and in front of the lens Used to correct near-sightedness (can see objects close up)

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Image formed in concave lens when the object is placed at infinity Images in Concave lens Image Virtual, erect & diminished f FF 2F Use In Galilean telescope

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Image formed in concave lens when the object is placed in front of lens object Images in Concave lens Image Virtual, erect & diminished v u f FF 2F Use In spectacles for correcting short-sightedness

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Applications of Lenses

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Cornea Iris Pupil Lens Optic nerve Retina Suspensor ligament

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