Glass Mein Pencil Tooti Kyun Dikhti Hai? ✏️
Ek glass mein paani bharo aur usme pencil daal do. Bagal se dekho — pencil paani ki satah par tooti hui lagti hai! Nikaal kar dekho — bilkul saabut hai.
Wajah? Paani se aati hui roshni jab hawa mein nikalti hai toh mud jaati hai. Aapka dimaag phir bhi maanta hai ki roshni seedhi aayi hai — isliye pencil ka doobi hua hissa kahin aur dikhta hai.
📌 Jab roshni ek medium (maadhyam) se doosre medium mein jaati hai (jaise hawa se paani, ya hawa se kaanch), toh wo apni disha badal leti hai. Isi ko refraction (apvartan) kehte hain.
Sochiye aap cycle chala rahe hain — pakki sadak se seedha reti (sand) par tirchhe
ja rahe hain. Jo pahiya pehle reti mein pahunchega wo
dheema ho jaayega, par doosra pahiya abhi bhi tez chal raha hoga. Nateeja? Cycle
apne aap mud jaayegi.
Roshni ke saath bilkul yahi hota hai. Roshni ka ek "morcha (wavefront)" hota hai. Jab wo tirchha
kaanch mein ghusta hai, uska ek sira pehle dheema ho jaata hai — aur poori ray (kiran)
mud jaati hai.
Isliye asli wajah hai: alag medium mein roshni ki RAFTAAR alag hoti hai.
Aur agar roshni bilkul seedhi (perpendicular) ghuse? Tab dono sire ek saath dheeme honge
— koi mudav nahi! Isiliye perpendicular girti ray bilkul seedhi nikal jaati hai.
📜 Refraction Ke Do Niyam
📌 Niyam 1: Incident ray, refracted ray aur normal — teeno
ek hi tal mein hote hain.
📌 Niyam 2 — Snell ka niyam:
sin i / sin r = n21 (ek sthirank)
Yahan n21 = doosre medium ka pehle ke saapeksh refractive index (apvartanank).
🎯 Kaunsi taraf mudegi — do line ka niyam:
🔹 Kam ghane se zyada ghane medium mein (hawa → kaanch) → normal ki
TARAF mudti hai, aur r < i
🔹 Zyada ghane se kam ghane mein (kaanch → hawa) → normal se
DOOR mudti hai, aur r > i
🔹 i = 0° (perpendicular) → bilkul nahi mudti
🔢 Refractive Index — Ek Number Mein Poori Baat
Refractive index batata hai ki koi medium roshni ko kitna dheema karta hai — aur isi se pata chalta hai ki roshni kitna mudegi.
📐 Nirpeksh (absolute) refractive index:
n = c / v
Yahan c = vacuum mein roshni ki raftaar = 3 × 108 m/s,
aur v = us medium mein roshni ki raftaar.
Kyunki roshni vacuum mein sabse tez chalti hai, n hamesha 1 se bada hota hai. Aur
n ki koi ikai (unit) nahi hoti — ye do raftaaron ka ratio (anupaat) hai.
| Medium | n | Roshni ki raftaar |
|---|---|---|
| Vacuum / hawa | 1.00 | 3.00 × 108 m/s |
| Barf (ice) | 1.31 | 2.29 × 108 m/s |
| Paani | 1.33 | 2.26 × 108 m/s |
| Kerosene | 1.44 | 2.08 × 108 m/s |
| Kaanch (crown glass) | 1.52 | 1.97 × 108 m/s |
| Heera (diamond) | 2.42 | 1.24 × 108 m/s |
Kaanch ka refractive index 1.5 hai. Kaanch mein roshni ki raftaar kya hogi?
Hal: n = c/v → v = c/n
v = (3 × 108) / 1.5 = 2 × 108 m/s
Yani kaanch mein roshni hawa se ek-tihaai dheemi ho jaati hai. Yahi dheemapan use
modta hai.
Paani ka n = 1.33 aur kaanch ka n = 1.50 hai. Kaanch ka paani ke saapeksh
refractive index nikaalo.
Hal: nglass, water = nglass / nwater
= 1.50 / 1.33 = 1.128
Aur ulta? nwater, glass = 1.33 / 1.50 = 0.887
✅ Dhyaan do: ye dono ek doosre ke ulta (reciprocal) hain —
1/1.128 = 0.887. Aur jab roshni kaanch se paani mein jaaye toh n 1 se
kam hai, matlab roshni normal se door mudegi.
Roshni hawa se kaanch (n = 1.5) mein 60° ke kon par ghusti hai. Angle of refraction
nikaalo.
Hal: sin i / sin r = n
sin 60° / sin r = 1.5
0.866 / sin r = 1.5
sin r = 0.866 / 1.5 = 0.577
r = 35.3°
✅ Jaanch: r (35.3°) < i (60°) — sahi hai, kyunki roshni kam ghane se zyada
ghane medium mein gayi hai, toh normal ki taraf mudni chahiye thi.
Heere ka n = 2.42 hai — kisi bhi aam paardarshi cheez se zyada. Iska matlab do
baatein:
1️⃣ Roshni heere ke andar bahut dheemi (1.24 × 108 m/s) chalti hai aur
bahut zyada mudti hai.
2️⃣ Uska critical angle (kraantik kon) sirf 24.4° hai — bahut chhota. Isliye andar ghusi roshni
baar-baar total internal reflection (paraavartan) karke andar hi andar uchhalti rehti hai, aur
aakhir mein ek saath bahar nikalti hai.
Isiliye heere ko khaas kon par kaata (cut) jaata hai — taaki roshni zyada se zyada
andar uchhle. Ek "achhe cut" ka heera usi kachche patthar se kai guna zyada chamakta
hai. Yani heere ki chamak sirf patthar se nahi, physics ki samajh se aati hai.
🧱 Kaanch Ki Silli — Do Baar Mudna
Upar wale diagram mein dhyaan se dekho: roshni do baar mudti hai — ek baar ghuste waqt, ek baar nikalte waqt. Aur nateeja bahut khoobsurat hai:
📌 Emergent ray incident ray ke bilkul PARALLEL hoti hai.
Kyun? Kyunki ghuste waqt roshni normal ki taraf mudi (i > r), aur nikalte waqt utna hi normal se
door mudi. Dono mudav ek doosre ko kaat dete hain.
Par ray apni asli line par wapas nahi aati — wo thodi khisak (shift) jaati hai. Isi
khisakne ko lateral displacement (paarshvik displacement) kehte hain.
🔍 Lateral displacement (visthapan) kab zyada hoga?
🔹 Silli jitni moti ho, utna zyada
🔹 Angle of incidence (aapaat kon) i jitna bada ho, utna zyada
🔹 Refractive index n jitna zyada ho, utna zyada
Aur agar i = 0° ho (perpendicular)? Tab displacement bhi zero — ray bilkul seedhi paar
nikal jaati hai.
💎 Total Internal Reflection — Jab Roshni Bahar Hi Na Nikle
Ab ek mazedaar sawaal: roshni kaanch se hawa mein ja rahi hai, toh wo normal se door mudegi. Ab i ko dheere-dheere badhaate jao... r bhi badhta jaayega. Ek waqt aayega jab r = 90° ho jaayega — yani ray satah ke saath-saath chalne lagegi!
📌 Jis i par r bilkul 90° ho jaata hai, use critical angle (critical
angle, C) kehte hain.
Aur agar i > C ho? Tab roshni bahar nikal hi nahi paati — wo
poori ki poori andar hi reflected ho jaati hai. Isi ko
Total Internal Reflection (total internal reflection) kehte hain.
📐 sin C = 1 / n
| Medium | n | Critical angle (C) |
|---|---|---|
| Paani | 1.33 | 48.8° |
| Kaanch | 1.50 | 41.8° |
| Heera | 2.42 | 24.4° |
⚠️ TIR ke liye DO shartein — dono zaroori hain:
1️⃣ Roshni zyada ghane se kam ghane medium mein ja rahi ho (kaanch → hawa)
2️⃣ Angle of incidence critical angle se bada ho (i > C)
Sirf ek shart poori ho toh TIR nahi hoga.
Optical fibre baal se bhi patli kaanch ki ek naali hoti hai. Roshni usme itne
tirchhe kon par bheji jaati hai ki har baar deewar par
i > C ho — matlab har baar TIR.
Nateeja? Roshni fibre ke andar uchhalti-uchhalti hazaron kilometre chali jaati hai,
bina bahar nikle aur lagbhag bina kamzor hue. Fibre mod do — roshni phir bhi mod ke saath-saath chali
jaati hai!
Aaj samundron ke neeche bichhi optical fibre cable se hi poori duniya ka internet
chalta hai. Bharat ka BharatNet project laakhon gram panchayaton tak yahi fibre
bichha raha hai. Aur doctor jis endoscope se pet ke andar dekhte hain, wo bhi isi
par chalta hai.
Ek chapter ka ek niyam — aur usi par aaj ki poori digital duniya khadi hai.
Garmiyon mein sadak par door paani jaisa chamakta dikhna — jise
mrig-trishna (mirage) kehte hain — Rajasthan aur Gujarat mein aam nazaara hai. Ye
bhi TIR hi hai!
Kaise? Zameen ke bilkul paas ki hawa bahut garam aur isliye
kam ghani ho jaati hai. Upar ki hawa thandi aur zyada ghani hai. Aasman se aati
roshni upar se neeche jaate hue thodi-thodi mudti rehti hai, aur ek jagah
i > C ho jaata hai — roshni upar ki taraf reflected ho jaati
hai.
Aapki aankh us roshni ko seedhi maankar sochti hai ki neeche aasman ka pratibimb hai — yani
paani! Isiliye mirage mein hamesha "paani" dikhta hai, kyunki wo asal mein
aasman ka image hai.
🧠 Apne Aap Ko Test Karo
💎 Explorer mein ray ko drag karke critical angle paar karo aur TIR hote dekho!
Open Refraction Explorer →