Reflection
* Based on the nature of the reflecting surface, reflection can be regular and irregular.
* Images can be real images that can be caught on a screen, or virtual images that cannot be caught on a screen. Images formed in a plane mirror are virtual.
According to the laws of reflection:
* The angle of incidence (i) equals the angle of reflection (r).
* The incident ray, the reflected ray and the normal all lie in the same plane.
* The image formed in a plane mirror is erected, laterally inverted, the same size as the object, and the distance of the image from the mirror is equal to the distance of the object from the mirror.
* To view the complete image of an object, you need a mirror that is at least half the height of the object.
* For a given incident ray, if the plane mirror is rotated through a certain angle, then the reflected ray rotates through twice that angle.
* The ratio f the height of an image to the height of an object is called linear magnification. The magnification can be unity, greater than one, or less than one.
* Number of images produced, when two mirrors are placed at an angle, θ, is calculated using the formula:
N = (360 / Θ) – 1
Spherical Mirrors
* A spherical mirror is made from a part of a hollow sphere of glass.
* Focal length of a spherical mirror is half of its radius of curvature.
* A convex mirror reflects light from its outer spherical surface and has a silver coating on its inner surface.
* A concave mirror reflects light from its inner spherical surface and has a silver coating on its outer surface.
* In convex mirrors, the location of the object does not affect the characteristics of the image.
* The nature and size of the image in a concave mirror depends on relative position of the object from the mirror.
* The ratio of the height of an image to the height of an object is called linear magnification. Magnification can be unity, greater than one, or less than one.
* The mirror formula defines the relationship between the focal length of the mirror, the object distance and the image distance. The formula is:
1/f=1/v+ 1/u
Refraction Basics
* The tendency of light to bend at the point of separation of two media is called refraction.
* The ratio of velocity of light in the first medium to that in the second medium is known as the refractive index of the second medium with respect to the first medium.
* The ratio of velocity of light in air or vacuum to that in a medium is called the absolute refractive index (μ) of the medium.
* According to Snell’s law, the ratio between the values of the sine of angle of incidence and the sine of angle of refraction for two given optical media is constant.
µ = sin i / sin r
* Critical angle is the angle of incidence in a denser medium, for which angle of refraction in the rarer medium is 90°.
* Total internal reflection occurs when the angle of incidence is greater than the critical angle. In such cases, the refracted ray bends by more than 90°, and gets reflected back into the same denser medium.
* The perpendicular distance between incident ray and emergent ray after passing through a glass slab is called lateral shift.
* The change in position of the object and image when seen through a denser medium is called vertical shift.
Refraction by Spherical Lenses
* A lens is a piece of transparent optical material with one or two curved surfaces to refract light rays.
* A convex lens has a surface that bulges outwards on both sides.
* A concave lens has inward bent surfaces on both sides.
* The distance between the optic centre and the focal point is called the focal length.
* Magnification is the ratio of image size to object size. It is also measured as the ratio of image distance to object distance.
m = ( Size of image / Size of object ) or m = (Image distance / Object distance )
According to the lens formula:
1/f=1/v+ 1/u
Where,
f = focal length
u = object distance
v = image distance