TOPIC-Light (Reflection and Refraction )

POWER POINT PRESENTATION..

Light is a form of

energy. It is needed

to see things

around us.

Light enables us

to see objects from

which it comes or

from which it is

reflected.

Light exhibits

the properties

of both waves and particles.

LIGHT

The process of sending back the light rays which fall on the surface of an object is called reflection of light.

1.A bundle of light rays is called a beam of light.2.The ray of light which falls on the mirror surface is

called the incident ray.3.The ray of light which is sent back by the mirror is

called the reflected ray.4.The normal is a line at right angle to the mirror

surface at the point of incidence.

REFLECTION OF LIGHT…..

1.The incident ray, the reflected ray, and the normal (at the point of incidence) all lie in the same plane.2.The angle of incidence is always equal to the angle of reflection.

LAWS OF REFLECTION……

REAL IMAGE1.The image which can

be obtained on a screen is called a real image.

2.A real image is always inverted.

3.The image formed on a cinema screen is an example of real image.

1.The image which cannot be obtained on a screen is called a virtual image.

2.A virtual image is always erect.

3.The image of our face in a plane mirror is an example of virtual image.

TYPES OF IMAGES….VIRTUAL IMAGE

1.The image formed in a plane mirror is virtual and erect.

2.The image in a plane mirror is of the same size as the object.

3.The image formed by a plane mirror is at the same distance behind the mirror as the object is in front of it.

4.The formed in a plane mirror is laterally inverted.

CHARACTERISTICS OF A PLANE MIRROR….

1.They are used to see ourselves.

2.They are fixed on the inside walls of certain shops(like jewellery shops) to them look bigger.

3. They are used in making periscopes.

4.They are fitted at blind turns of some busy roads so that drivers can see the vehicles coming from the other side and prevent accidents.

USES OF PLANE MIRRORS….

1.CONCAVE MIRROR:A Concave mirror is that sherical mirror in which the reflection of light takes place at the bent-in surface.

USES1.They are used as shaving mirrors to

see a large image of the face.2.They are used by dentists to see the

large images of the teeth of patients.3.They are used as reflectors in torches,

vehicle head – lights and search lights to get powerful beams of light.

TYPES OF MIRRORS AND THEIR USES….

A Convex mirror is that spherical mirror in

which the reflection of light takes place at

the bulging-out surface. USES

1.They are used as rear-view mirrors in vehicles.

2.They are also used as shop-security mirrors.

CONVEX MIRROR….

MIRROR FORMULA AND MAGNIFICATION(MIRROR)

MIRROR FORMULA 1/V + 1/U = 1/F , where v=image distance u=object distance f=focal length MAGNIFICATION The linear magnification produced by a mirror

is equal to the ratio of the image distance to the object distance, with a minus sign. m = hi/ho = - v/u , where hi=height of image ho=height of object m=linear magnification

REFRACTION OF LIGHT The bending of light rays when it goes from

one medium to another obliquely is called refraction of light.

1.A medium in which the speed of light is more is known as optical rarer medium.

2.A medium in which the speed of light is less is known as optically denser medium.

3.When a ray of light goes from a rarer to a denser medium, it bends towards the normal.

4.When a ray of light goes from a denser to a rarer medium, it bends away from the normal.

Laws of refraction

1.The incident ray, the refracted ray and the normal at the point of

incidence all lie in the same plane.

2.The ratio of the sine of angle of incidence to the sine of angle of refraction is constant for a given

media. Sini/Sinr= constant i.e refractive index

REFRACTIVE INDEXThe refractive index of a medium gives an indication of light-bending ability of

that medium.TYPES OF REFRACTIVE INDECES

1.ABSOLUTE REFRACTIVE INDEX:When light is going from vaccum to another medium, then the value of refractive index is called the absolute refractive index.

2.RELATIVE REFRACTIVE INDEX:When light is going from one medium (other than vaccum or air) to another medium, then the value of refractive index is called the relative refractive index.

REFRACTION THROUGH A GLASS SLAB….

1.• The light emerges

from a parallel-sided glass slab in a direction parallel with that in which it enters the glass slab.

2.

• The perpendicular distance between the original path of incident ray and the emergent ray coming out of the glass slab is called lateral displacement of the emergent ray of light.3.

• The angle which the emergent ray makes with the normal is called the angle of emergence.

SOME IMPORTANT POINTS (REFRATIVE INDEX)

1.The refactive index depends on the nature of the material of the medium and on the wavelength of the light used.

2.If any two media are optically exactly the same, then no bending occurs when light passes from one medium to another.

3.A substance having higher refractive index is optically denser than another substance having lower refractive index.

4.The refractive index for light going from medium 1 to medium 2 is equal to the reciprocal of the refractive index for light going from medium 2 to medium 1.

SOME IMPORTANT TERMS (LENS)

1.OPTICAL CENTRE:The centre point of a lens is known as optical centre.

2.PRINCIPAL FOCUS:The principal focus of a lens is a point on its principal to which light rays parallel to the principal axis converge or diverge after passing the lens.

3.FOCAL LENGTH: The focal length of a lens is the distance between optical centre and principal focus of the lens.

4.CENTRE OF CURVATURE:The centre of curvature of a lens is the centre of the hollow sphere of glass of which the lens is a part.

5.PRINCIPAL AXIS:The straight line passing through the centre of curvature and optical centre of a lens is called its principal axis.

LENS… A lens is a transaparent glass bound by

two spherical surfaces.TYPES OF LENS

CONVEX LENS: A Convex lens is thick at the centre but thinner at the edges.

CONCAVE LENS: A Concave lens is thick in the middle but thicker at the edges.

USES OF CONVEX LENS

1.They are used in spectacles to correct the defect of vision called hypermetropia (long sightedness).2.They are used for making a simple camera.3.They are used as a magnifying glass (or magnifying lens) by palmists, watchmakers etc.4.They are used in making making microscopes, telescopes and slide projectors (or film projectors).

USES OF CONCAVE LENS

1.They are used in spectacles to correct the defect the vison called called myopia.

2.They are used as eye-lens in galilean telescope.

3.They are used in combination with convex lenses to make high quality lens systems for optical instruments.

4.They are used in wide-angle spyhole in doors.

LENS FORMULA AND MAGNIFICATION(LENS)MIRROR FORMULA1/v -1/u = 1/f , where v=image distance u=object distance f=focal length MAGNIFICATION The linear magnification is the ratio of the heightof the image to the height of the object.m = hi/ho = v/u ,where hi=height of image ho=height of object m=linear magnification

MADE BY AADI AHLUWALIA CLASS 9 – CROLL NO. - 1