0 notes of light reflection and refraction
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Laws of Reflection
The angle of incidence is equal to angle of reflection
Incident ray, reflected ray and normal all lie in the same plane.
Spherical Mirrors
Most common type of curved mirrors are spherical mirrors.
Some Important Terms
Pole- The centre of the reflecting surface in a spherical mirror is a pole. It is represented by P.
Centre of curvature- Reflecting surface in a spherical mirror has a centre, this is known as centre of curvature.
Radius of curvature- The radius of the reflecting surface of the spherical mirror is known as radius of curvature. It is represented by R.
Principal axis- Straight line passing through the pole and centre of curvature in a spherical mirror is known as principal axis.
Principal focus- The reflected rays appear to come from a point on the principal axis, this is known as principal focus.
Focal length- The distance between the pole and the principal focus in a spherical mirror is known as focal length and it is represented by f.
Aperture- The diameter of the reflecting surface is defined as aperture.
Note: Radius of curvature is twice the focal length (R=2f).
Uses of Concave Mirror
Used in search lights, torches, head lights of the vehicles. Also used in shaving mirrors. Used by dentists also to see larger image of the teeth. Other use in solar furnaces.
Uses of Convex Mirror
They are used as rear-view mirrors. They are used to see the traffic behind. They are preferred as they give erect but diminished image.
New cartesian sign convention is used to give sign convention used for spherical mirrors. The conventions are as follows-
1. The object is always placed to the left of the mirror.
2. All distances parallel to the principal axis are measured from the pole of the mirror.
3. All the distances measured to the right of the origin (along + x-axis) are taken as positive while those measured to the left of the origin (along – x-axis) are taken as negative.
4. Distances measured perpendicular to and above the principal axis (along + y-axis) will be taken as positive.
5. Distances measured perpendicular to and below the principal axis (along –y-axis) will be taken as negative.
Mirror formula and magnification
The distance of the object from its pole is known as object distance (u), whereas distance from the pole of the mirror is known as image distance (v). The mirror formula is given by-
distance of the object from its pole is known as object distance
It is applicable for spherical mirrors in all positions of the object.
Magnification
It is defined as relative extent to which an object is magnified in comparison to its object size.
Refraction of light
Bending of the light rays as it passes from one medium to another medium is known as refraction of light.
Laws of Refraction
Incident ray, refracted ray and normal all lie in the same plane.
The ratio of sine of angle of incidence to the sine of angle of refraction is constant. This law is also known as Snell’s law of refraction.
Laws of refraction
Refractive Index
When light passes from one medium to another medium, it changes its direction. The extent to which the direction changes is expressed in terms of refractive index. The value of refractive index is dependent on the speed of light in two media. v1 is the speed of light in medium 1 and v2 is the speed of light in medium 2. The refractive index of medium 2 with respect to medium 1 is represented as n21.
Refractive index
If medium 1 is vacuum or air, then the refractive index of medium 2 with respect to vacuum is known as absolute refractive index of the medium.
vacuum or air, then the refractive index of medium
Where c is the speed of light in air, v is the speed of light in other medium and nm is the refractive index of the medium.
Refraction by Spherical Lenses
Lenses are defined as transparent materials which are bounded by two surfaces, out of which one or both can be spherical. When both the two spherical surfaces bulge outwards, it is known as convex lens. They converge the light rays. When the two spherical surfaces bulge inwards, they are known as concave lens. They are known as diverging lens. The centre of these spherical surfaces is known as centre of curvature, represented by C.
The centre point is known as optical centre. The effective diameter of the spherical lens is known as aperture.
Lens formula and magnification
The ratio of the height of an image to the height of an object is defined as magnification.
Power of a Lens
The reciprocal of focal length is known as its power.
P = 1/f