Reflection of Light

Reflection of light
   When light is incident on a smooth surface, it is partly sent back by the surface in the same medium through which it had come.This phenomenon is called reflections of light by the surface.

Reflection of light from plane mirror

   Let M1M2 be a plane mirror. A ray of light AO falls on the mirror at a point A and is reflected in a definite direction along AB. The ray  OA is 'incident ray' and the ray AB is 'refleted ray' . The point  ' A' on the mirror is called 'point of incidence' . The line AN drawn perpendicular to the mirror at the point of incidence is called normal. The angle between the incident ray OA and the normal AN is called the angle of incidence (i) and the angle between the reflected ray AB and the normal AN is called the angle of reflection (r).

    The reflection of light follows two laws :
1. The incident ray, the normal at the point of incidence and the reflected ray all lie in the same plane.
2. The angle of incidence (i) and the angle of reflection (r) are equal. 

   The experimental observation are called law of reflection.

     For normal incidence, i=0 and so r=0. Hence , a ray falling normally on a mirror is reflected back along its own path.

Distance and Displacement

Distance and Displacement 

       The position of a moving object goes on changing with respect to time. The length of the actual path covered by a body in a time interval is called 'Distance'. While the difference between the final and the initial positions of on object is called Displacement.

Distance is a scalar quantity which has magnitude only. Displacement is a vector quantity which has both magnitude and direction.

         If the initial position of object S1 and final position of object S2. 

When S2>S1     then S2 - S1 = S ,  the Displacement is positive

When S2<S1     then S2 - S1 = -S ,  the Displacement is negative

When S2=S1     then S2 - S1 = S = 0 , the Displacement is zero

      Displacement can also be positive, negative and zero but distance only positive.

    

Motion and Rest

MOTION

An object is said to be in motion if it's position change with respect to its surrounding in a given time.

REST

If the position of the object does not change with respect to it's surrounding it is said to be at rest.

Nature of Light

The question whether light is a wave or a particle has a very interesting and long history. Early theories considered light to be a stream of particle which emanated from a source and caused the sensation of vision upon entering the eye. The most influential proponent of this particle theory of light was Newton. Using it, he was able to explain the law of reflection and refraction. The chief proponents of the wave theory of light propagation were Christian Hygens and Robert Hooke. Hygen's using his wave theory was able to explain reflection and refraction. Newton was the virtues of the wave theory of light particularly as it explained the colour formed by thin films,  which Newton studied extensively. However, he rejected the wave theory because of the observed straight line propagation of light. Because of Newton's great reputation and authority, this reluctant rejection of the wave theory of light, best an lock of evidence of diffraction was strictly adhered to by Newton's followers. Newton's particle theory of light was accepted for more than a century.

    In 1801 Thomas Young receive the wave theory of light. He was one of the first to introduce the idea of interference as a wave phenomena in both light and sound. His observation of interference with light was a clear demonstration of the wave nature of light. Young's work went unnoticed by the the scientific community for more then a decade.

     Fresnel performed extensive experiments on interference and diffraction and the wave theory on a mathematical basis. He showed, that the rectilinear propagation of life is a result of very short wavelength of visible light. In 1850 Jean Foucault measured the speed of light in water and showed that it is less than that in air, thus ruling out Newton's particle theory according to whom the speed of light is more in water.
    But the drama was not yet over. The climax came when the wave theory of light failed to explain the photoelectric effect invented by Albert Einstein in 1905. He himself explained it on the basis of particle nature of light.  An amicable understanding was ultimately reached in accepting that light has dual nature. It can behave as particle as well as wave depending on its interaction with the surrounding. Later it was found that even the well established particles such as electrons also have a dual character and can she interference and diffraction under suitable condition.

What is physics ?

Physics is the study of nature its law.

Physics is a branch of science. The word "Physics" has come from a Greek word meaning nature. The word "Science" has come from a Latin word "Scientia" which means "to know".

         Each of these phenomena occurring in nature occurs under certain rules. The discovery and study of these rules is Physics.

         The physics is related to the basic rules which are applied in all areas of life such as Biology and Medical science etc. Physics, Science and Technology are the basic foundation for acquiring knowledge of all branches.