Chapter 5 Light-2

July 28, 2014  |  By  | 

Mr Ng Han Guan Form 4 Chapter 5: Light Guru Cemerlang Physics MSAB Date: 2 nd edition © 2011 | chp 5 | Maktab Sultan Abu Bakar | Sekolah Kluster Kecemerlangan 10 5.3.1 The Phenomenon Involving Total Internal Reflection of Lights 1. Mirage  On a hot day, a distant road will appear to have pools of water lying on the surface. This phenomenon calls as mirage.  It’s occurs is due to the different temperature layers of air, hot air on the ground is less dense compare with cold air at higher level on hot day.  The sun ray will travel from cool air layer to hot air layer (means from denser to less dense). The sun ray will always refract away from the normal.  The total internal reflection will occurs when the angle of incident ray is larger than critical angle and the light ray is reflected upwards.  Our eye sight sees straight as though there are pools of water (virtual image of reflection of sky) on the ground. 2. Rainbow  When sunlight shines on millions of water droplets in the air after rain, we see a colourful natural phenomenon called rainbow. It caused by refraction, dispersion* and total internal reflection of light within water droplets.  When white light from the sun enters the raindrops (less dense to denser), it is refracted and dispersed into its various colour components inside the raindrops.  When the dispersed light hits the back of the raindrop, it undergoes total internal reflection (denser to less dense, incident angle greater than critical angle).  It is then refracted again as it leaves the drop (incident angle less than critical angle). * Dispersion is the separation of white light into its component colours: ROYGBIV (Red, Orange, Yellow, Green, Blue, Indigo and Violet)

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