Winmeen Tnpsc Group 1 & 2 Self Preparation Course Physics UNIT 9. Ray Optics. surface at the point of incidence, all lie in the same plane.

Transcription

1 Laws of reflection Physics UNIT 9 Ray Optics The incident ray, the reflected ray and the normal drawn to the reflecting surface at the point of incidence, all lie in the same plane. The angle of incidence is equal to the angle of reflection. Characteristics of the image formed by a plane mirror Image formed by a plane mirror is as far behind the mirror as the object is in front of it and it is always virtual. The image produced is laterally inverted. The minimum size of the mirror required to see the complete image of the object is half the size of the object. If the mirror turns by an angle θ, the reflected ray turns through an angle 2θ. The centre of the sphere, of which the mirror is a part is called the centre of curvature (C). The geometrical centre of the mirror is called its pole (P). 1 Learning Leads to Ruling

2 Principal axis - The line joining the pole of the mirror and its centre of curvature The distance between the pole and the centre of curvature of the spherical mirror is called the radius of curvature. The linear or transverse magnification is defined as the ratio of the size of the image to that of the object. The angle of incidence in the denser medium at which the refracted ray just grazes the surface of separation is called the critical angle. The power of a converging lens is positive and that of a diverging lens is negative. The refractive index of a medium is always said to be positive. The magnification is negative for real image and positive for virtual image. In the case of a concave lens, it is always positive. The power of a lens (P) is defined as the reciprocal of its focal length. Dispersion is the splitting of white light into its constituent colours. This band of colours of light is called its spectrum. 2 Learning Leads to Ruling

3 The dispersive power of the material of a prism is defined as the ratio of angular dispersion for any two wavelengths (colours) to the deviation of mean wavelength. The spectrometer is an optical instrument used to study the spectra of different sources of light and to measure the refractive indices of materials The collimator is an arrangement to produce a parallel beam of light. The angle of deviation of a ray by a plane mirror or a plane surface is twice the glancing angle. A beam of light is a collection of rays. Light from a lamp travels in all directions which is a divergent beam. A convex lens produces a convergent beam of light, when a parallel beam falls on it. Highly polished metal surfaces reflect about 80% to 90% of the light incident on them. For the same incident ray, when the mirror is rotated through an angle, the reflected ray is rotated through twice the angle. 3 Learning Leads to Ruling

4 An object placed in front of a plane mirror has an image behind the mirror When a parallel beam of light is incident on a spherical mirror, the point where the reflected rays converge (concave mirror) or appear to diverge from the point (convex mirror) on the principal axis is called the principal focus (F) of the mirror. The distance between the pole and the principal focus is called the focal length (f) of the mirror. The images produced by spherical mirrors may be either real or virtual In a convex mirror irrespective of the position of the object, the image formed is always virtual, erect but diminished in size. The image lies between the pole and the focus The refractive index of diamond with respect to air is Its critical angle is o The total internal reflection is the basic principle of optical fibre. An optical fibre is a very thin fibre made of glass or quartz. 4 Learning Leads to Ruling

5 Light year is a unit of distance used in astronomy. A light year is the distance travelled by light in one year. It is equal to metre When a ray of light travels from one transparent medium into another medium, it bends while crossing the interface, separating the two media. This phenomenon is called refraction. The unit of power of lens is diopter Power of lens is positive for converging lens and negative for diverging lens A prism is a transparent medium bounded by the three plane faces. The polished faces of prism are called refracting faces The angle between the refracting faces is called angle of prism, or the refracting angle. 5 Learning Leads to Ruling

6 IMPORTANT FORMULAS Velocity of light as per Michelson s method c = NnD 6 Learning Leads to Ruling