Tiêu đề RAY OPTICS & OPTICAL INSTRUEMENTS.pdf ✅

 Digital www.allendigital.in [ 3 ] Introduction Optics: Optics is the branch of physics in which we study the behaviour and properties of light, including its interactions with matter. Light is that part of electromagnetic waves which gives sensation to our eyes. f    Properties of light 1. Speed of light in vacuum, denoted by c = 3 × 108 m/s approximately. 2. Light carries energy and momentum. 3. Light is electromagnetic wave (proposed by Maxwell). It consists of varying electric and magnetic field. 4. Light is an electromagnetic wave and transverse in nature. 5. The formula v = f  is applicable to light. Note: Eye is most sensitive for yellowish green colour and least sensitive for violet and red colours. Rectilinear propagation of light Rectilinear propagation describes the tendency of electromagnetic waves (light) to travel in a straight line path in homogenous medium. Ray A ray of light is the straight-line path of transfer of light energy. Arrow represents the direction of propagation of light. Figure shows a ray which indicates light is moving from A to B. Beam A bundle or bunch of rays is called a beam. It is of following three types : (a) Convergent beam : In this case diameter of beam decreases in the direction of ray. (b) Divergent beam : It is a beam in which all the rays meet at a point when produced backward and the diameter of beam goes on increasing as the rays proceed forward. Radio waves Microwaves Infrared Visible Region Ultraviolet X-rays Gamma rays Ray Optics and Optical 01 Instruments B E propagation of light A B ray
NEET : Physics [ 4 ] www.allendigital.in  Digital (c) Parallel beam : It is a beam in which all the rays constituting the beam move parallel to each other and diameter ofbeam remains same. Under many circumstances, the wavelength of light is negligible compared with the dimensions of the device as in the case of ordinary mirrors and lenses. A light beam can then be treated as a ray whose propagation is governed by simple geometric rules. The part of optics that deals with such phenomenon is known as geometrical optics. Reflection of Light When light rays strike the boundary of two media such as air and glass, a part of light is turned back into the same medium. This is called Reflection of Light. Laws of Reflection (1) The incident ray, the reflected ray and the normal at the point of incidence lie in the same plane. This plane is called the plane of incidence (or plane of reflection). This condition can be expressed mathematically as e. n r 0 ˆ ˆ ˆ (  =) Where; ê is a unit vector along incident ray. n̂ is a unit vector along normal. r̂ is a unit vector along reflected ray. (2) The angle of incidence (the angle between normal and the incident ray) and the angle of reflection (the angle between the reflected ray and the normal) are equal, i.e. i = r Note: (a) The frequency, wavelength and speed of light do not change after reflection. (b) If we draw a tangent at the point of incident then the angle between incident ray and tangent is equal to the angle between reflected ray and tangent. In case of plane mirror angle between incident ray and plane mirror is same as angle between reflected ray and plane mirror. OPTICS Ray Optics (Geometrical Optics) Wave Optics Study of light in the form of ray Study of light in the form of wave i i normal i i normal  i  i i i   Parallel beam of light normal   O Incident Ray Reflected Ray Medium 1 Transmitted Ray or Refracted Ray Medium 2 Incident Ray Medium 1 Medium 2 Reflected Ray Transmitted Ray or Refracted Ray
Ray Optics and Optical Instruments  Digital www.allendigital.in [ 5 ] Types of Reflection 1. Regular Reflection: When the reflection takes place from a perfect plane surface it is called Regular Reflection. In this case the reflected light has large intensity in one direction and negligibly small intensity in other directions. Eg :- reflection from mirror. 2. Diffused Reflection: When the surface is rough, we do not get a regular behaviour of light. Although at each point light ray gets reflected irrespective of the overall nature of surface, difference is observed because even in a narrow beam of light there are many rays which are reflected from different points of surface, and it is quite possible that these rays may move in different directions due to irregularity of the surface. This process enables us to see an object from any position. Such a reflection is called as diffused reflection. Eg :- reflection from a wall, newspaper etc. Object and Image Object: Light rays incident on an optical element is responsible to define object. Object is defined as the point of intersection of incident rays. Image: Light rays formed after interaction (either reflection or refraction) with an optical element is responsible to define image. Image is defined as the point of intersection of reflected or refracted rays. Note: A real image can be captured on a screen. This image on the screen can be perceived by the eye. What about virtualimages? Since they cannotbe capturedona screenis itpossible tosee them. From practical experience we know that we can see ourselves in a plane mirror which is indeed a virtual image. So, it is possible to see a virtual image. But how is it done? There is a lens in our eye that focuses the diverging set of rays on to the retina forming a real image inside our eyes. In a similar manner, a camera can also convert a virtual image into a real imagewhich is captured on the film. Real Object Virtual Object O O O Virtual Object Incident Rays Converging Diverging Virtual Object Real Object Real Object Virtual Object O O Real Object O Real object Virtual image O I O Virtual Object Real Image I Real Image Virtual Object O I Reflected "OR" Refracted Rays Converging Diverging Real Image Virtual Image Real object Virtual image O I O Virtual Object Real Image I Real Object Virtual Image O I
NEET : Physics [ 6 ] www.allendigital.in  Digital Reflection from Plane Mirror A plane mirror is a mirror with a flat (planar) reflective surface. Image formation in plane mirror Diverging light rays leave the source (object) and are reflected from the mirror, obeying the law of reflection. Upon reflection, the rays continue to diverge. The dashedlines infigure arebackwardextensions of the diverging rays back to a point of intersection atI. The diverging rays appear to originate atthe point I behind the mirror to the observer. PointI, which is behind the mirror, is called the image of the object at O. Perpendicular distance of object from plane mirror is equal to perpendicular distance of image from plane mirror. Characteristics of image due to reflection by a plane mirror: (i) Distance of object from mirror = Distance of image from the mirror. (ii) All the incident rays from a point object will meet or appear to meet at a single point after reflection from a plane mirror which is called image. (iii) The line joining a point object and its image is normal to the reflecting surface. For example: Plane mirror Thin Glass slab silvering Reflecting surface Polished surface A plane mirror behaves like a window to a virtual world. Polished surface Reflecting surface Silvering Thin Glass Slab Plane mirror object image O d d O Object d d image I O I x x 10 cm 10 cm d d O I d d 10 cm 10 cm O I