KNOWLEDGE FACTORIAL 0703

KNOWLEDGE FACTORIAL

(

BY:SURAJ SINGH RAWAT

Contact:7895437652

YouTube channel: KNOWLEDGE FACTORIAL

INSTAGRAM:surajrawat.0703)

Reflection of Light: The phenomenon of bouncing back of light into the same medium

by the smooth surface is called reflection.

Incident light: Light which falls on the surface is called incident light.

Reflected light: Light which goes back after reflection is called reflected light.

The angle of incidence: The angle between the incident ray and the normal.

An angle of reflection: The angle between the reflected ray and the normal.

Mirror: The surface which can reflect the light is a mirror.

Plane Mirror: If the reflecting surface is a plane then the mirror is plane.

Spherical Mirror: If the reflecting surface is part of the hollow sphere then the mirror is

a spherical mirror.

The spherical mirror is of two types:

• Convex mirror: In this mirror reflecting surface is convex. It diverges the light so it is also

called a diverging mirror.

• Concave mirror: In this mirror reflecting surface is concave. It converges the light so it is

also called converging mirror.

Parameters of Mirror:

Center of Curvature: The centre of hollow sphere of which mirror is a part. The radius of curvature: The radius of hollow sphere of which mirror is a part.

• Pole: The centre of mirror (middle point) is pole.

• Principal axis: The line joining the pole and center of curvature is called principal axis.

• Aperture: Size of mirror is called aperture of mirror.

• Principal Focus: The point on the principal axis, where all the incident rays parallel to principal axis converge or diverge after reflection through mirror.

• Focal Length: The distance between pole and focus point is focal length.

Special Rays for Formation of Image:

• A ray of light which is parallel to the principal axis of a spherical mirror, after reflection converges or diverges from focus.

• A ray of light passing through or appearing from the center of curvature of spherical mirror is reflected back along the same path.

• A ray of light passing through or appearing from the focus of spherical mirror becomes parallel to the principal axis.

• A ray of light which is incident at the pole of a spherical mirror is reflected back making same angle with principal axis.

Use of Concave Mirror: It is used as a makeup mirror, the reflector in torches, in

headlights of cars and searchlights, doctor’s head-mirrors, solar furnace, etc.

Sign Conventions of Spherical Mirror

• All the distances are measured from the pole of the mirror as the origin.

• Distances measured in the direction of incident rays are taken as positive.

• Distances measured opposite to the direction of incident rays are taken as negative.

• Distances measured upward and perpendicular to the principal axis are taken as positive.

• Distances measured downward and perpendicular to the principal axis are taken as negative.

1f

=

+

Linear Magnification: This is the ratio of the height of the image to the height of the

object.

m=

…where m = magnification, h = height of image, h’ = height of object

Use of Convex Mirror: Convex mirror used as rear view mirror in vehicles, as shop

security mirrors, etc.

KNOWLEDGE FACTORIAL

(

BY:SURAJ SINGH RAWAT

Contact:7895437652

YouTube channel: KNOWLEDGE FACTORIAL

INSTAGRAM:surajrawat.0703)

Mirror formula and Magnification

Mirror formula

1u

+

=

Refractive index:

Refractive index: The ratio of speed of light in vacuum (c) to the speed of light in any

medium (v) is called refractive index of the medium.

Relative refractive index:

The relative refractive index of a medium with respect to other medium is the ratio of

speed of light in the second

Here, n

= Relative refractive index of medium 1 with respect to medium 2.

14. Some applications of refraction:

• Bottom of a tank or a pond containing water appears to be raised due to refraction.

• When a thick glass slab is placed over some printed matter, the letters appear raised when viewed through the glass slab.

• When a pencil is partly immersed in water, it appears to be displaced at the interface of air and water.

• A lemon kept in water in a glass tumbler appears to be bigger than its actual size, when viewed from sides.

Lens: A transparent medium bound by two surfaces, of which one or both surfaces are spherical.

15. Convex lens: A lens may have two spherical surfaces, bulging outwards. Such a lens

is called a double convex lens or convex lens.

• It is thicker at the middle as compared to the edges.

• Convex lens converges light as shown in Figure above.

Hence, convex lenses are called converging lens.

16. Concave lens: A double concave lens is bounded by two spherical surface curved

inwards.

• It is thicker at the edges than in the middle.

• Concave lens diverges light and is called diverging lens.

17. Basic terms of spherical lens:

• Principal axis: A line joining the centre of curvatures of two spherical surfaces forming a lens is called principal axis. The line joining C1 and C2 is the principal axis (see figure

below).

• Principal focus: A point on the principal axis of a lens where all rays of light parallel to the principal axis meet (figure a) or appears to meet (figure b) after passing through the lens is called principal focus of the lens.

• Optical centre: The central point of a lens (O) through which a ray of light pass undeviated is called optical

• Focal length: The distance between the principal focus and optical centre of a lens is called focal length of lens. It is denoted by f.

• Aperture of lens: The effective diameter of circular outline of a spherical lens is called its apperture.

18. Rules for making ray diagram

1. A ray of light from the object, parallel to the principal axis, after refraction from a lens

passes through the principal focus or appears to diverge from the principal focus

2. A ray of light passing through the principal focus or appearing to meet at the principal

focus after refraction, will emerge parallel to the principal axis.

. A ray of light passing through the optical centre of lens will emerge without any deviation.

. Ray diagram for the image formation by convex lens:

21. Image formation by concave lens: Position of the objectPosition of the

imageRelative size of the imageNature of the imageAt infinityAt focus F

Highly

diminished, point-sizedVirtual and erectBetween infinity and optical 1 centre 0 of the

lensBetween focus F

and optical centre 0DiminishedVirtual and erect

22. Sign convention of spherical lens:

• Sign conventions of lens is same as sign convention of mirrors

• The focal length of convex lens is positive and concave lens is taken as negative.

23. Lens formula and magnification:

1v

−

=

u = object distance

v = image distance

f= focal length

24. Magnification (m)

Magnification is defined as the ratio of the height of image to the height of object.

m=

=

=

I = height of image,O = height of object

25. Power of a lens

The power of a lens is defined as reciprocal of its focal length.

P=

f = focal length (in metre) The SI unit of power is ‘dioptre’. It is denoted by the letter D.

1 dioptre is the power of a lens whose focal length is 1 metre, 1 D = 1 m

• Power of convex lens is positive and concave lens is negative.

• 26. Combination of lens 1fnet

=

+

fnet= Net focal length fx = focal length of lens 1 f2 = focal length of lens 2

P net = Power of combination P1 = Power of lens 1

P2 = Power of lens 2.