Lenses

What are lenses? Lens – a thin, transparent piece of glass or plastic that has at least one curved side The sides may be concave, convex, or plane Lenses that make parallel light rays come together (converge) are called converging lenses Lenses that make parallel light rays move apart (diverge) are called diverging lenses

Lenses Lenses that make parallel light rays come together (converge) are called converging lenses Lenses that make parallel light rays move apart (diverge) are called diverging lenses

Images Formed By A Converging Lens Three rays may be used when locating an image in a converging (convex) lens: Ray is parallel to the PA from object and is refracted through the focal point on the far side of the lens Ray passes directly through the centre of the lens Ray passes through the focal point on the same side of the lens and refracts parallel to PA

Images Formed By A Converging Lens S – smaller A – inverted L – between F and 2F T - real

Converging Lenses Can Produce Different Types of Lenses Images formed by a converging lens will differ depending on whether the object is at one of 5 possible locations: Beyond 2F At 2F Between 2F and F At F Inside F

Object at 2F F 2F F S – same A – inverted L – at 2F T - real

Object Between F and 2F F 2F F S – larger A – inverted L – past 2F T - real

Object at F F 2F F NO CLEAR IMAGE

Object Within F F 2F F S – larger A – upright L – other side of object T - virtual

Image Characteristics of a Converging Lens Object Image Location Size Attitude Type Beyond 2F At 2F Between 2F and F At F Inside F between 2F and F real smaller inverted same inverted at 2F real larger inverted beyond 2F real No clear image larger upright behind object virtual Optics Bench

Optical Devices – uses of Lenses Where must the lens be placed? A copy camera produces an image that is real and the same size A hand magnifier produces an image that is virtual and larger A slide projector produces an image that is real and larger A 35-mm camera produces an image that is real and smaller A spotlight produces parallel light: there is no image A photographic enlarger produces an image that is real and larger 2F from the object Inside F Between F and 2F Beyond 2F At F Between F and 2F