converging lenses
DESCRIPTION
TRANSCRIPT
Converging
Lens
LENSESLenses are mainly made of glass clear
plastics. They are widely used in spectacles, cameras, telescopes and many other optical instruments.
Our human eye has two crystalline lenses which enable us to form images.
Lenses
There are two main types of lenses:• convex lenses—these curve outwards and
are fatter in the middle• concave lenses—these curve inwards (a
little like a cave) and are thinner in the middle.
Convex lenses Concave Lenses
Lenses – An application of refractionThere are 2 basic types of lenses
A converging lens (Convex)takes light rays and bringthem to a point.
A diverging lens (concave) takes light rays and spreads them outward.
Convex Mirrors
Curves outwardReduces imagesVirtual images
Use: Rear view mirrors, store security…
CAUTION! Objects are closer than they appear!
Convex Lenses
Thicker in the center than edges. Lens that converges
(brings together) light rays.
Forms real images and virtual images depending on position of the object
The Magnifier
focus (f)focus (f) 2 f2 fx x x x
Parallel rayPasses thruThe focus
Focal ray
Refracts parallelTo principal axis
A ray thru theCenter of the
lenses
Remains unbent
MOVEMENT OF LIGHT THROUGH LENSES
CONVEX LENS In a convex lens, an incoming ray parallel to the
principal axis is refracted through the principal focus (F).
Movement of Light through a Lens
The distance from the centre line (plane) of the lens to the principal focus is called the focal length of the lens.
A ray passing through the centre of either type of lens is unaffected.
As with all images, rays of light that come from a part of the object come together again at that same part of the image.
Finding the focal lengthRays coming into a lens from a distant
object are almost parallel and form an image very close to the focus.
We can then measure the distance from lens to image to determine the focal length of the lens.
The greater the curvature of a lens, the more it bends light and hence the shorter the focal length.
Focal Length
Convex lenses produce two different types of images, depending on where the object is located.
If the object is at a distance greater than the focal length of the lens, a real image is formed.
Image type and Location
If the object is at a distance less than the focal length of the lens, a virtual image is formed.
Convex Lenses
REAL AND VIRTUAL IMAGESReal Image –
Image is made from “real” light rays that converge at a real focal point so the image is REAL
Can be projected onto a screen because light actually passes through the point where the image appears
Always invertedVirtual Image–
“Not Real” because it cannot be projected
Image only seems to be there!
Parallel ray
focus (f)focus (f) 2 f2 fx x x x
Focal ray
Image is:RealInvertedReducedAppears between f and 2f
Object beyond 2f
focus (f)focus (f) 2 f2 fx x x xFocal ray
Parallel ray
Image is:RealInvertedSame sizeAppears between f and 2f
Object at 2f
focus (f)focus (f) 2 f2 fx x x xFocal ray
Parallel ray
Image is:RealInvertedEnlargedAppears beyond 2f
Object betweenf and 2f
focus (f)focus (f) 2 f2 f
x x x x
Image is:VirtualErectEnlargedAppears on sameSide as Object
ApparentConvergence
Of rays
ObjectInsidefocus
APPLICATIOSNS
OPTICAL INSTRUMENTS Telescopes Telescopes make small, far objects appear larger. Two lenses are used. The objective lens produces a real, inverted image
just inside the focus of a second lens, called the eyepiece lens. The image produced by the first lens now acts as the object for the second lens. Because the first image is inside the focus of the second lens, the second image (the one seen by the telescope user) is virtual and enlarged compared to the first one
CAMERAS, IN BRIEF
In a pinhole camera, the hole is so small that light hitting any particular pointon the film plane must have come from a particular direction outside the camera
In a camera with a lens, the same applies: that a point on the film planemore-or-less corresponds to a direction outside the camera. Lenses havethe important advantage of collecting more light than the pinhole admits
pinholeimage atfilm plane
object
image atfilm plane
object
lens
JAZAKALLAH!
PREPARED BY:
CLASS:XI-OM. FAHD-UN-NABI KHAN