Shikshakendra

  ~CHAPTER AT A GLANCE ▪︎ 1).Metals : metals show metallic  lustre, are generally hard,malleable   and ductile. They are good conductors of heat and electricity.    2).Metals are sonorous : metals produce a sound when they strike a hard surface. We Express it by saying that metals are sonorous. That it why school bells are made of  metals.  3). Non metals : substances like carbon, sulphur and iodine are non metals. They are either solid or gas with the exception of bromine which is liquid.  4).Exceptions :  (i) Metals in general have high melting points. But mercury, gallium and Celsium have low melting points and are liquids at room temperature. (ii) Iodine, a non-metal, show lustre. (iii) Diamond, an allotrope of carbon, is the hardest natural substance known. Graphite, another allotrope of carbon, is a conductor of electricity. 

  CHAPTER AT A GLANCE  1. An optical prism has two triangular bases and three rectangular lateral surfaces, which are inclined to each other. Angle between it's two lateral faces is called the angle of prism.   Whenever, refraction of light takes place through a prism, the emergent ray is called the angle of deviation D.   2. When a beam of white light passes through a glass prism, it splits up into its constituent seven colours. These seven colours are remembered by the acronym 'VIBGYOR'. The splitting of white light into its component colours is called 'dispersion of light's. The band of the coloured components formed due to dispersion is called 'spectrum'.      Dispersion is on account of different amount of deviations for light of different colours. Red coloured ray bends the least but violet ray bends the most. Thus, spectrum is formed.  Seven colours of VIBGYOR can be recombined so as to form white light . 3. Rainbow is a natural spectr...