10th Class Physics Chapter 3 Notes Urdu Medium

Complete Notes on Chapter No.12:  10th Class Physics Chapter 3 Notes Urdu Medium in 10th Class Physics Urdu Medium written by Professor Sir Fahad Abbas Suib. These computerized notes are very helpful in the preparation of Geometrical Optics Class 10 for students of the 10th class Physics and these are according to the paper patterns of all Punjab boards.

• Our comprehensive 10th Class Physics Chapter 3 Notes Urdu Medium will ensure you're fully prepared for your exams.
• When light travelling in a certain medium falls on the surface of another medium, a part of it turns back in the same medium. This is called reflection of light. 
• There are two laws of reflection: i. The incident ray, the reflected ray, and the normal all lie in the same plane. ii. The angle of incidence is equal to the angle of reflection (i.e., i = r).
• Like plane surfaces, spherical surfaces also reflect light satisfying the two laws of reflection.
• In mirrors, image formation takes place through reflection of light while in lenses image is formed through refraction of light.
• The equation relating the distance of the object p from the mirror/lens, distance of the image q and the focal length f of the mirror/lens is called mirror/lens formula, given by 1 / f = 1 / p + 1 / q 
• Magnification of a spherical mirror or thin lens is defined as “the ratio of the image height to the object height.” i.e.   Magnification m = Image height / Object height = hi / h
• Power of a lens is defined as “the reciprocal of its focal length in metres”. Thus Power of a lens = P = 1 / focal length in metres. The SI unit of power of a lens is “Dioptre”, -1 denoted by a symbol D. If f is expressed in metres so that 1 D = 1 m^-1. Thus, 1 Dioptre is the power of a lens whose focal length is 1 metre.
• The refractive index ‘n’ of a material is the ratio of the speed of light ‘c’ in air to the speed of light ‘v’ in the material, thus n = Speed of light in air  / Speed of light in medium = c / v
• The bending of light from its straight path as it passes from one medium into another is called refraction.
• Refraction of light takes place under two laws called laws of refraction. These are stated as: 
• i.The incident ray, the refracted ray, and the normal at the point of incidence all lie in the same plane. 
• ii. The ratio of the sine of the angle of incidence ‘i’ to the sine of the angle of refraction ‘r’ is always equal to a constant i.e. sin i / sin r = constant.  Where the ratio sin i / sin r is equal to the refractive index of the second medium with respect to the first medium.  i.e.  sin i / sin r = n  This is also called Snell's law.
• The angle of incidence for which the angle of refraction becomes 90° is called critical angle. When the angle of incidence becomes larger than the critical angle, no refraction occurs. The entire light is reflected back into the denser medium. This is known as total internal reflection of light.
• A simple microscope, also known as a magnifying glass, is a convex lens which is used to produce magnified images of small objects.
• A compound microscope is used to investigate structure of small objects and has two converging lens, the objective and the eyepiece.
• Telescope is an optical instrument which is used to observe distant objects using lenses or mirrors. A telescope that uses two converging lenses is called refracting telescope. A telescope in which the objective lens is replaced by a concave mirror is called reflecting power telescope.
• The magnifying power is defined as “the ratio of the angle subtended by the image as seen through the optical device to that subtended by the object at the unaided eye”.
• The resolving power of an instrument is its ability to distinguish between two closely placed objects.
• The ability of the eye to change the focal length of its lens so as to form a clear image of an object on its retina is called its power of accommodation.