geometric optics

GEOMETRIC OPTICS

DEFINITION:

“The branch of optics that focuses on the creation of images is called

geometric optics”.

RULES OF GEOMETRIC OPTICS:

• Light is a flow of photons with wavelengths.

We'll call these as “light rays.”• Light rays travel in straight lines in free space.• Light rays do not interfere with each other as

they cross.• Light rays obey the laws of reflection and

refraction.• Light rays travel from the light sources to the

Eye.

PRINCIPLE:

The principle objective of geometric optics is to be able to determine the

location of an

image for certain optical elements arrange in a specific geometry.

This may be accomplished in two ways:

1. One can sketch key ray paths in a scale drawing of the geometry.

2. one can calculate the image distance and properties using a set of equations.

BASICS:

1.REFLECTION:PLANE MIRRORSPHERICAL MIRROR

2.REFRACTION:SPHERICAL LENSES

REFLECTION

PLANE MIRROR:

A plane mirror is a mirror with a planar reflective surface.

For light rays striking a plane mirror, the angle of reflection equals the angle of incidence.

IMAGE FORMATION BY PLANE MIRROR

If you stand in front of a plane mirror you see your image behind the mirror. The location of the image can be diagramed knowing that the surface of the mirror reflects light with an angle of reflection equal to the incident angle.

PROPERTIES OF IMAGE:

It is formed• behind the mirror • it is right side up• having same size as that of object• Far behind the surface as the object is in front

of it.• We refer to the image as virtual image.

REFLECTION BY SPHERICAL MIRROR:

DEFINITION:A reflecting surface having the form of a portion of a

sphere is called a spherical mirror.

TYPES:1. Concave mirror

2. Convex mirror

SPHERICAL MIRROR:

RAY DIAGRAMS POINTS:• One surface of the curved mirror is

silvered. • The centre of the sphere is called the

centre of curvature C.• The geometrical centre of the mirror is

called its pole (P)• The line joining the pole of the mirror and

its centre of curvature is called the principal axis.

Cont..

• When a parallel beam of light is incident on a spherical mirror, the point where the reflected ray converge on the principal axis is called the principal focus F.

The Concave Mirror:

“If the reflecting surface lies on the inside of the curve, is a concave mirror”.

RULES:

• Rays parallel to the principle axis are reflected towards the principle focus of the mirror.

• A ray passing through the centre of curvature retraces its path after reflection.

Cont..

• A ray passing through the principal focus , after reflection is rendered parallel to the principal axis.

• A ray of light which strikes the mirror at its pole gets reflected according to the law of reflection.

IMAGE FORMATION IN CONCAVE MIRROR:

• When the object is placed at the centre of curvature

the image is of same size, real and inverted and is at the centre.

CASE 1:

CASE 2:

• When the object is placed after the centre of curvature, it is seen that the image is real , inverted, small in shape and lies between the centre C and focus F.

CASE 3:

• When the object is placed within the focus of the mirror it is seen that image is virtual, erect and enlarged in shape and lies behind the mirror.

CASE 4:

• When the object is between the centre of curvature and focus ,it is seen that image is real, inverted and enlarged and lies outside the centre of curvature.

CONVEX MIRROR:

“ If the reflecting surface lies on the outside of the curve, is a convex mirror”.

RULES:

• A ray of light traveling parallel the principal axis after reflection from a convex mirror appears to come from its focus behind the mirror

• A ray of light traveling towards the centre of curvature behind the mirror and is reflected back its own path.

IMAGE FORMATION IN CONVEX MIRROR:

• The object is placed anywhere in front of the convex mirror.

• The ray parallel to the principal axis after reflection appears to come from the focus F behind the mirror.

• Another ray going towards the centre of curvature C behind the mirror gets reflected by the same path.

• The two reflected rays appear to intersect at a point between F and P behind the mirror.

• the image appears to be formed behind the mirror.

• So the image formed by the convex mirror is virtual, erect and smaller in size with respect to object.

USES OF SPHERICAL MIRRORS:

CONVEX MIRROR:• Sunglasses• Vehicles• Security• Magnifying Glass

CONCAVE MIRROR:• Vehicle• Light Concentration

IMAGE DISTANCE

• All virtual images have negative image distances

• and all real images have positive image distances.

REFRACTION

CONVEX LENS:

“It is a converging lens such that a beam of light passing through it is brought to a point or focus”.

Image Distance:

• An image located behind the lens has a positive image distance.

Concave Lens:

“It is a diverging lens such that a parallel beam of light passing through it is caused to diverge or spread out”.

Image Distance:

• An image distance marked off in front of the lens is considered negative

USES OF SPHERICAL LENSES:

Uses of concave lens:• Telescopes• Spectacles• Door hole lenses

Uses of convex lens:• Telescopes• Spectacles• Microscopes