Video narration
Aakhir mirror mein chehra kyon dikhta hai, lekin paani ka straw tedha kyon lagta hai? Mirror se takrakar roshni wapas lautti hai. Ise reflection, yaani paravartan, kehte hain. Paani mein pravesh karte hi straw se aane wali roshni mudti hai. Yeh refraction, yaani apavartan, hai - prakash ka ek paaradarshi maadhyam se doosre mein jaana. Yahi fark hai: mirror light ko bounce karaata hai, water mein uski speed badalti hai, isliye light bend karti hai. Optical denser medium bhaari nahin hota; usmein prakash dheema chalta hai. Reflection ka niyam hai: angle of incidence equals angle of reflection. Yeh angles satah se nahin, normal se maape jaate hain - normal satah par perpendicular kheechi gayi kaalpanik line hai. Refraction ka angle bhi normal ke saapeksh samajhte hain; maadhyam badalne par speed badalti hai. Isliye mirror mein chehra reflection se dikhta hai, aur straw paani ke refraction se bent lagta hai.