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.

Lenses THERE ARE ALWAYS TWO REFRACTIONS IN A LENS

Lenses Two basic shapes Converging lens Diverging lens

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

Converging Lens OPTICAL CENTRE: the exact centre of the lens

Ray diagrams for Converging Lenses

Images through Converging Lenses Let’s practice

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

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

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

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

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

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

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

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

Diverging Lens

Ray diagrams for Diverging Lenses

Images through Diverging Lenses Let’s practice

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)

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

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

Applications of Lenses

Cornea Iris Pupil Lens Optic nerve Retina Suspensor ligament

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