CBSE Class 10 Science Light Reflection And Refraction Notes Set B

Mirror formula for spherical mirrors :-
The mirror formula for spherical mirrors is the relationship between the object distance (u), image distance (v) and focal length (f). The mirror formula is expressed as :-
1/v + 1/u = 1/t

Magnification for spherical mirrors:-
Magnification for spherical mirrors is the ratio of the height of the image to the height of the object.
Magnification = Height of the image / Height of the object
i.e. m = h_i / h_o

The magnification is also related to the object distance and image distance. It is expressed as :-
M = h_i / h_o = – (v / u)
The position of the image for various positions of the object for a concave mirror is as shown in the table below. The table also shows the use of the mirror for different positions of the object.

The position of the image for various positions of the object for a convex mirror is as shown in the table below. The table also shows the use of the mirror for different positions of the object.

Image formation by a concave lens.

Power of Lens: The degree of convergence or divergence of light rays achieved by a lens is called power of lens. S.I. unit of power of lens is dioptre.
Formula P =1/f where f is the focal length
Power of convex lens is positive and power of concave lens is negative.

Assertion and Reason Type Questions
Refractive indices of kerosene, turpentine and water are 1.44, 1.47 and 1.333 respectively. Through which of these media, light travels fast? Explain.
Speed of light in a madium = c/n = 3 x 10⁸ ms^-1 / n

Since, refractive index of water (1.333) is less than the refractive indices of kerosene and turpentine, so light travels faster in water than in kerosene and turpentine.
Refractive indices of media A, B, C and D are given below: