Mirror se Light ka Converge aur Diverge (Roshni Ikatthi ya Bikhri?)
Ek mirror dhoop ko ek chhote chamakte dot mein jama kar deta hai, doosra use phaila deta hai. Kaise? Chalo dekhte hain! 🥣☀️
🧭 Is Post Mein
📖 Kahani: Katori ka Jaadui Dot
Dopahar ka samay tha. Aangan mein dhoop chamak rahi thi aur mummy ne steel ke bartan dhoop mein sukhaane rakhe the. Golu ne ek chamakti steel ki katori uthayi aur use Suraj ki taraf ghuma diya.
“Arre dekho! Zameen pe ek chhota sa, bahut tez chamakta dot ban gaya!” Golu chillaya.
Priya ne paas padi sapaat steel ki thaali uthayi aur wahi kiya. “Meri thaali se toh ek bada sa halka dhabba banta hai, chhota dot nahi.” Phir usne katori ko ulta karke uski bahar wali (ubhri) sateh Suraj ki taraf ki. Ab roshni chaaron taraf phail gayi aur koi dot nahi bana.
Rohan bhaiya muskuraye: “Teen bartan, teen nateeje! Thaali roshni ko seedha lautati hai, katori ka andar wala hissa roshni ko ikattha karta hai, aur bahar wala hissa roshni ko phaila deta hai. Science mein ise kehte hain converge aur diverge. Aur haan, us dot ko kabhi aankh se ya haath pe mat lena, woh garam hota hai!”
Pichhle post mein humne reflection ke niyam seekhe. Aaj dekhenge ki jab bahut saari parallel kirnein plane, concave aur convex mirror pe girti hain, toh kya hota hai. 🔍
🎯 Is Post Mein Kya Seekhenge
- Parallel kirnein (parallel rays) kya hoti hain, aur dhoop ki kirnein parallel kyun maani jaati hain
- Plane mirror pe parallel kirnein reflection ke baad parallel hi rehti hain
- Concave mirror parallel kirnon ko converge (paas laana / ikattha karna) karta hai
- Convex mirror parallel kirnon ko diverge (door karna / phailaana) karta hai
- Har kiran i = r maanti hai, phir bhi pattern alag kyun banta hai
- Concave mirror se dhoop ikatthi karke garmi paana, aur solar concentrator kya hota hai
🧱 Basics: Pehle Yeh Aana Chahiye
1. Parallel lines: do ya zyada seedhi lines jo hamesha barabar doori pe chalti hain aur kabhi nahi milti, jaise railway ki do patriyan.
2. Reflection ke niyam: har kiran ke liye i = r (kon normal se naapte hain), aur incident ray, normal, reflected ray ek hi samtal mein.
3. Concave aur convex: concave mirror ki chamakdaar sateh andar ki taraf mudi hoti hai (jaise katori ka andar), convex ki bahar ki taraf ubhri (jaise katori ka bahar ya chammach ki peeth).
Niyam bhool gaye? Pichhla post dekh lo: Reflection ke Niyam.
💡 Concept: Ikattha Karo ya Phailao
Step 1: Parallel kirnein. Jab kai kirnein ek hi disha mein, ek-doosre ke barabar chalti hain, toh unhe parallel beam kehte hain. Suraj humse itna door hai ki uski jo kirnein humare chhote se mirror tak pahunchti hain, woh lagbhag parallel hoti hain.
Step 2: Plane mirror pe. Plane mirror sapaat hai, isliye uske har point pe normal ek hi disha mein hota hai. Har kiran ka i barabar hai, toh har kiran ka r bhi barabar. Nateeja: reflected kirnein bhi parallel hi rehti hain. Isliye thaali se bada, ek-jaisa dhabba banta hai.
Step 3: Concave mirror pe. Concave mirror ek bade khokhle gole ka andar wala hissa hai. Uske har point pe normal gole ke kendra (centre) ki taraf jaata hai, yaani alag-alag points pe normal alag disha mein. Kinaare ki kiran zyada mudti hai, beech ki kam. Nateeja: reflected kirnein ek-doosre ki taraf mud kar paas aati hain. Ise converge karna kehte hain.
Step 4: Convex mirror pe. Convex mirror gole ka bahar wala hissa hai. Yahan normal kendra se bahar ki taraf jaate hain. Isliye reflected kirnein ek-doosre se door hoti jaati hain. Ise diverge karna kehte hain.
🔸 Diverge = kirnon ka door jaana, phail jaana (convex mirror)
🔸 Parallel = kirnein na paas aayein, na door jaayein (plane mirror)
Step 5: Niyam toota kya? Bilkul nahi! Har ek kiran apne point pe i = r hi maanti hai. Farq sirf itna hai ki curved mirror pe har point ka normal alag disha mein hota hai. Isi wajah se poori beam ka pattern badal jaata hai.
Step 6: Ikatthi roshni = garmi. Concave mirror bade area pe giri dhoop ko ek chhote se area pe ikattha kar deta hai. Utni hi roshni ki energy chhoti jagah pe aa jaaye, toh wahan bahut tez roshni aur garmi hoti hai. Isiliye katori ka dot itna chamakdaar tha, aur kaagaz pe der tak rakhne se kaagaz jal bhi sakta hai.
Step 7: Phaili roshni. Convex mirror roshni ko bade area mein phaila deta hai, isliye dhabba halka padta hai. Yahi phailaav convex mirror ko bada area dikhane layak banata hai (jaise gaadi ka side mirror).
🖼️ Diagrams: Picture se Samjho
🔐 Deep Concept: Focus, Garmi aur Ulta Raasta
Raaz 1: Focus (F). Concave mirror pe uski beech wali line (principal axis) ke parallel kirnein aayein, toh reflection ke baad woh lagbhag ek hi point pe milti hain. Is point ko focus kehte hain. Mirror se focus ki doori ko focal length kehte hain. Yeh shabd aap badi classes mein vistaar se padhoge; abhi bas itna yaad rakho ki chamakta dot isi point ke paas banta hai.
🔸 Matlab: mirror jitna zyada muda (chhoti radius), dot utna paas banega.
Raaz 2: Convex ka focus “nakli” kyun? Convex mirror ki kirnein phail jaati hain, woh kahin nahi milti. Par agar unhe peeche ki taraf (mirror ke andar) badhao, toh woh mirror ke peeche ek point se aati hui lagti hain. Wahan sach mein roshni nahi pahunchti, isliye wahan kaagaz pe dot kabhi nahi banega.
Raaz 3: Garmi kitni guna? Maan lo mirror 100 cm² dhoop pakadta hai aur use 1 cm² ke dot mein ikattha kar deta hai. Toh dot pe har cm² pe lagbhag 100 guna zyada roshni girti hai (asal mein thodi roshni kho jaati hai, isliye thoda kam). Isiliye bada concave mirror zyada garmi deta hai: woh zyada dhoop pakadta hai.
Raaz 4: Ulta raasta (reversibility). Roshni jis raaste se aati hai, ulta bhejo toh usi raaste se laut jaati hai. Parallel kirnein F pe milti hain, toh F pe rakhe bulb ki roshni mirror se lautkar parallel ho jaati hai. Yahi torch aur headlight ka raaz hai.
✏️ Examples: Converge, Diverge ya Parallel?
Plane mirror ke har point pe normal ek jaisa, toh sab kirnein ek jaisi mudti hain.
Andar ki taraf mudi sateh = concave mirror.
Bahar ubhri sateh = convex mirror.
f ≈ R ÷ 2 = 40 ÷ 2 = 20 cm (chhote mirror ke liye).
200 ÷ 2 = 100. Kuch roshni kho jaati hai, isliye asal mein thoda kam.
Ulta raasta: focus se nikli roshni concave mirror se parallel ho kar lautti hai.
⚖️ Difference Table: Teen Mirror, Parallel Kirnein
| Baat | Plane mirror | Concave mirror | Convex mirror |
|---|---|---|---|
| Sateh | Sapaat | Andar ki taraf mudi | Bahar ki taraf ubhri |
| Normal ki disha | Har point pe ek jaisi | Kendra ki taraf (andar) | Kendra se bahar |
| Parallel kirnein lautne ke baad | Parallel rehti hain | Paas aati hain (converge) | Phail jaati hain (diverge) |
| Dhoop ka dhabba | Mirror jitna bada, ek jaisa | Chhota, bahut tez dot | Bada, halka; koi dot nahi |
| Kaagaz jala sakta hai? | Nahi | Haan (sambhal ke!) | Nahi |
| Upyog | Ghar ka sheesha | Torch, headlight, solar cooker | Gaadi ka side mirror, mod ke mirror |
🚫 Misconceptions: Log aisa sochte hain… lekin
❌ “Curved mirror reflection ke niyam nahi maanta, isliye kirnein mudti hain.”
✅ Sach: har kiran i = r maanti hai; bas har point pe normal ki disha alag hai.
❌ “Convex mirror roshni ko kam kar deta hai ya kha jaata hai.”
✅ Sach: woh roshni ko sirf phailata hai. Utni hi roshni bade area mein bant jaati hai, isliye har jagah halki lagti hai.
❌ “Concave mirror khud garmi paida karta hai.”
✅ Sach: garmi Suraj ki roshni se aati hai; mirror sirf us roshni ko ek jagah ikattha karta hai.
❌ “Converge ka matlab hai kirnein mirror ke andar chali jaati hain.”
✅ Sach: kirnein mirror se lautti hain aur mirror ke saamne ek jagah paas aa kar milti hain.
❌ “Mirror Suraj ki taraf karke us chamakte dot ko dekhna theek hai.”
✅ Sach: ikatthi dhoop aankh ko gambhir nuksaan pahuncha sakti hai. Dot sirf kaagaz pe dekho, kabhi aankh, chehre ya twacha pe nahi.
🔤 Key Terms (Exam mein English shabd hi likhna)
❓ FAQs
1. Dhoop ki kirnein sach mein parallel hoti hain kya?
Suraj bahut bada aur bahut door hai. Uske kisi bhi ek point se humare chhote mirror tak aane wali kirnein lagbhag parallel hoti hain. Isliye science mein dhoop ko parallel beam maan lete hain.
2. Katori ka dot har baar ek hi jagah kyun nahi banta?
Dot focus ke paas sabse chhota aur tez banta hai. Kaagaz focus se aage-peeche ho toh dhabba bada aur halka ho jaata hai. Isliye activity mein kaagaz ki doori adjust karte hain.
3. Convex mirror se kaagaz kyun nahi jalta?
Convex mirror roshni ko phaila deta hai, ek jagah ikattha nahi karta. Phaili roshni se garmi bahut kam milti hai.
4. Kya plane mirror bhi kabhi roshni ikatthi kar sakta hai?
Ek plane mirror nahi. Par bahut saare chhote plane mirror alag-alag kon pe laga kar sabki dhoop ek jagah bheji jaa sakti hai. Bade solar plant isi tarah kaam karte hain.
5. Kya chamakte dot pe haath rakh kar dekh sakte hain kitna garam hai?
Bilkul nahi! Haath jal sakta hai. Garmi dekhni ho toh sirf kaagaz ka tukda use karo, wo bhi kisi bade ki nigraani mein.
🧪 Activity (NCERT): Kai Kirnein, Teen Mirror
Saamaan: ek plane mirror, ek concave mirror, ek convex mirror, mirror stand, torch, kanghi (comb), kaala kaagaz, paper clip, safed kaagaz.
Bhaag 1: Parallel kirnein, teen mirror
🔹 Plane mirror: lauti kirnein bhi parallel.
🔹 Concave mirror: lauti kirnein paas aati hain (converge).
🔹 Convex mirror: lauti kirnein phail jaati hain (diverge).
Bhaag 2: Dhoop ikatthi karo (sirf kisi bade ki nigraani mein)
Nishkarsh: concave mirror dhoop ko ek chhote point pe ikattha karta hai, wahan itni garmi banti hai ki kaagaz jal sakta hai. Har kiran reflection ke niyam maanti hai, par curved sateh poori beam ko converge (concave) ya diverge (convex) kar deti hai.
Yeh activity NCERT ki Class 8 Science book Curiosity (Chapter 10) par aadharit hai, aur yahan apne shabdon mein samjhayi gayi hai.
🏠 Mini Experiments (Ghar pe)
Isse kya pata chala? Thaali (plane) roshni seedhi lautati hai, katori ka andar (concave) roshni ikatthi karta hai, aur bahar (convex) phailata hai.
Chamakti steel ki badi chammach lo. Torch ki roshni uske andar wale hisse pe daalo aur saamne safed kaagaz pakdo; kaagaz aage-peeche karke sabse chhota dhabba dhoondo. Phir chammach palat kar peeth pe roshni daalo. Ab chhota dhabba ban hi nahi paata, roshni phail jaati hai.
Copy pe ek bada gola (compass se) banao aur uska ek chhota hissa mirror maano. Teen-chaar parallel kirnein kheencho. Har kiran jahan gire, wahan gole ke kendra se ek line (normal) kheencho aur protractor se i = r leke reflected kiran banao. Dekho, kirnein paas aati hain!
🧠 Think Like a Scientist
Sawaal: Golu ke paas ek gehri chhoti katori hai aur ek kam gehri badi parat (dono ka andar chamakdaar). Dhoop ka dot kiske paas banega, mirror se kam doori pe?
Scientist ka tareeka dekho
1. Observe (dekho): dono concave sateh hain, dono dot banati hain, par doori alag lagti hai.
2. Guess (anumaan): Golu ka anumaan: badi parat ka dot paas banega kyunki woh badi hai.
3. Test (jaanch): Rohan bhaiya ki nigraani mein dono se dhoop kaagaz pe daali, kaagaz aage-peeche karke sabse chhota dot dhoondha, aur scale se mirror se kaagaz ki doori naapi. Teen baar naap kar ausat liya.
4. Result: gehri katori ka dot paas bana, kam gehri parat ka dot door.
5. Conclusion: jitna zyada muda (gehra) concave mirror, kirnein utni jaldi milti hain, yaani focus utna paas. Size se nahi, mudaav se doori tay hoti hai. Anumaan galat nikla, aur test se sach pata chala! 🔬
🌍 Real Life Mein
- 🔦 Torch aur headlight: bulb ke peeche concave reflector hota hai. Bulb focus ke paas hone se roshni seedhi beam ban kar door tak jaati hai.
- 🍲 Solar cooker (dish wala): badi chamakdaar concave dish dhoop ko beech mein rakhe bartan pe ikattha karti hai aur khaana pakta hai. Bina gas, bina bijli!
- 🏭 Solar concentrator aur furnace: mirrors se dhoop ikatthi karke paani garam karke bhaap banayi jaati hai, jisse bijli banti hai ya badi rasoi mein khaana pakta hai. Kuch solar furnace itne garam hote hain ki steel tak pighla dete hain.
- 📡 Dish antenna: TV ki dish bhi concave hoti hai. Woh door se aaye signals ko converge karke beech mein lage receiver pe ikattha karti hai.
- 🚗 Gaadi ka side mirror: convex mirror kirnon ko phailata hai, isliye peechhe ka bada area chhote mirror mein dikh jaata hai.
🔁 Recap: Poora Post Ek Nazar Mein
- Dhoop ki kirnein lagbhag parallel hoti hain.
- Plane mirror: parallel kirnein lautne ke baad bhi parallel.
- Concave mirror: parallel kirnon ko converge karta hai (paas laata hai).
- Convex mirror: parallel kirnon ko diverge karta hai (phailata hai).
- Har kiran i = r maanti hai; curved sateh pe normal ki disha badalne se pattern badalta hai.
- Concave mirror dhoop ikatthi karke kaagaz jala sakta hai: solar cooker, solar concentrator, solar furnace isi pe chalte hain.
- Bulb focus pe ho toh concave reflector parallel beam deta hai (torch, headlight).
✍️ Fill in the Blanks
- Kirnon ka reflection ke baad paas aana ______ kehlaata hai.
- Convex mirror parallel kirnon ko ______ karta hai.
- Plane mirror se lautne ke baad parallel kirnein ______ hi rehti hain.
- Dhoop ko chhote area pe ikattha karne wale yantra ko solar ______ kehte hain.
- Concave mirror pe har point ka normal gole ke ______ ki taraf hota hai.
- Torch mein bulb concave reflector ke ______ ke paas rakha jaata hai.
Answers
1) converge · 2) diverge · 3) parallel · 4) concentrator · 5) kendra (centre) · 6) focus
✅ True / False
- Concave mirror parallel kirnon ko diverge karta hai.
- Curved mirror pe bhi har kiran i = r maanti hai.
- Convex mirror dhoop ikatthi karke kaagaz jala sakta hai.
- Plane mirror ke har point pe normal ek hi disha mein hota hai.
- Concave mirror khud garmi paida karta hai.
- Gaadi ki headlight mein concave reflector hota hai.
Answers (kyun ke saath)
1) False: concave mirror converge karta hai; diverge convex karta hai.
2) True: niyam har mirror pe chalte hain, bas normal ki disha badalti hai.
3) False: convex roshni phailata hai, ikattha nahi karta.
4) True: isiliye parallel kirnein parallel hi lautti hain.
5) False: garmi Suraj ki roshni se aati hai; mirror sirf use ek jagah ikattha karta hai.
6) True: bulb focus ke paas hone se door tak jaati seedhi beam banti hai.
🔘 MCQs
Q1. Parallel kirnein plane mirror pe girti hain. Lauti kirnein kaisi hongi? (a) Converge (b) Diverge (c) Parallel (d) Gayab ho jaayengi
✅ (c): plane mirror pe sab normal ek jaise, toh sab kirnein ek jaisi lautti hain.
(a) converge concave mirror karta hai.
(b) diverge convex mirror karta hai.
(d) chamakdaar mirror roshni lautata hai, gayab nahi karta.
Q2. Concave mirror parallel beam ke saath kya karta hai? (a) Converge karta hai (b) Diverge karta hai (c) Parallel rakhta hai (d) Roshni ko andar sokh leta hai
✅ (a): andar mudi sateh kirnon ko paas laati hai.
(b) yeh convex ka kaam hai.
(c) yeh plane mirror ka kaam hai.
(d) mirror roshni lautata hai, sokhta nahi.
Q3. Convex mirror se lauti parallel kirnein: (a) Parallel rehti hain (b) Converge hoti hain (c) Mirror ke saamne ek point pe milti hain (d) Phail jaati hain
✅ (d): convex mirror diverge karta hai.
(a) plane mirror ke liye sahi hai.
(b) aur (c) concave mirror ke liye sahi hain.
Q4. Har kiran i = r maanti hai, phir bhi concave mirror kirnon ko converge kyun karta hai? (a) Concave mirror niyam nahi maanta (b) Har point pe normal ki disha alag hoti hai (c) Roshni curved sateh pe dheemi ho jaati hai (d) Concave mirror roshni ko garam karta hai
✅ (b): normal gole ke kendra ki taraf hota hai, jo har point pe alag disha hai.
(a) galat, niyam har mirror pe chalte hain.
(c) reflection mein roshni ki raftaar ka koi role nahi.
(d) garmi kaaran nahi, nateeja hai.
Q5. Dhoop se kaagaz jalaane wali activity mein kaunsa mirror use hota hai? (a) Plane (b) Convex (c) Concave (d) Koi bhi
✅ (c): sirf concave mirror dhoop ko chhote dot mein ikattha karta hai.
(a) plane mirror roshni parallel rakhta hai, ikattha nahi karta.
(b) convex phailata hai.
(d) har mirror se yeh nahi hota.
Q6. Solar concentrator kya karta hai? (a) Dhoop ko chhote area pe ikattha karta hai (b) Dhoop ko phailata hai (c) Bijli se roshni banata hai (d) Dhoop ko rokta hai
✅ (a): mirrors/lenses se dhoop ek jagah jama karke garmi paata hai.
(b) yeh ulta hai.
(c) woh Suraj ki roshni use karta hai, bijli se roshni nahi banata.
(d) rokna uska kaam nahi.
Q7. Gaadi ki headlight mein bulb ke peeche kaisa reflector hota hai? (a) Plane (b) Concave (c) Convex (d) Koi reflector nahi
✅ (b): concave reflector focus pe rakhe bulb ki roshni ko parallel beam bana deta hai.
(a) plane se beam door tak seedhi nahi jaati.
(c) convex roshni phaila deta.
(d) headlight mein reflector hota hai.
Q8. Convex mirror ki lauti kirnon ko peeche badhao toh woh kahan se aati lagti hain? (a) Mirror ke saamne ek point se (b) Seedhe Suraj se (c) Har jagah se (d) Mirror ke peeche ek point se
✅ (d): kirnein phailti hain, par peeche badhane pe mirror ke peeche ek point (nakli focus) se aati lagti hain.
(a) yeh concave ke saath hota hai.
(b) Suraj se toh aane wali kirnein aati hain, lauti hui nahi.
(c) lauti kirnon ka ek pakka pattern hota hai.
🔗 Assertion–Reason
Options: (a) A aur R dono sahi, aur R, A ko samjhata hai · (b) A aur R dono sahi, par R, A ko nahi samjhata · (c) A sahi, R galat · (d) A galat, R sahi
1. A: Concave mirror se dhoop kaagaz jala sakti hai. R: Concave mirror parallel kirnon ko converge karke chhote area pe ikattha karta hai.
✅ (a): dono sahi, aur roshni ka chhote area pe ikattha hona hi garmi aur jalne ki wajah hai.
2. A: Convex mirror pe giri parallel beam reflection ke baad phail jaati hai. R: Convex mirror reflection ke niyam nahi maanta.
✅ (c): A sahi hai. R galat hai, har kiran i = r maanti hai; phailaav normal ki badalti disha se hota hai.
3. A: Solar cooker ke liye convex mirror sabse achha hai. R: Convex mirror kirnon ko diverge karta hai.
✅ (d): A galat hai, solar cooker mein dhoop ikatthi karni hoti hai, jo concave karta hai. R sahi hai.
📝 Very Short Answer (1 mark)
1. Kaunsa mirror parallel kirnon ko converge karta hai?
Concave mirror.
2. “Diverge” ka matlab kya hai?
Kirnon ka ek-doosre se door phail jaana.
3. Activity mein kai parallel kirnein banane ke liye kya kiya?
Kanghi ke kai daanton ke beech ki jagah khuli rakhi (multiple slits).
4. Plane mirror se lauti parallel kirnein kaisi hoti hain?
Parallel.
5. Ikatthi dhoop se steel pighlaane wali bhatti ko kya kehte hain?
Solar furnace.
📝 Short Answer (2–3 marks)
1. Plane, concave aur convex mirror pe parallel kirnein girne pe kya hota hai?
Plane mirror pe lauti kirnein parallel rehti hain. Concave mirror pe woh paas aati hain (converge). Convex mirror pe woh phail jaati hain (diverge).
2. Reflection ke niyam maante hue bhi concave mirror kirnon ko kaise milata hai?
Har kiran apne point pe i = r maanti hai. Par concave mirror ke har point pe normal gole ke kendra ki taraf hota hai, yaani har point pe alag disha mein. Isliye kinaare ki kirnein zyada aur beech ki kam mudti hain, aur sab ek jagah ki taraf aa jaati hain.
3. Concave mirror se kaagaz kyun jal sakta hai? Ek savdhani bhi likho.
Concave mirror bade area pe giri dhoop ko ek chhote dot mein ikattha karta hai, wahan bahut garmi banti hai aur kaagaz jal sakta hai. Savdhani: Suraj ya reflect hoti dhoop mein kabhi mat dekho, aur kisi bade ki nigraani mein hi karo.
4. Torch mein concave reflector kaise madad karta hai?
Bulb reflector ke focus ke paas hota hai. Bulb ki jo roshni reflector pe girti hai, woh lautkar parallel beam ban jaati hai, isliye roshni bikharti nahi aur door tak seedhi jaati hai.
📝 Long Answer (5 marks)
1. Comb aur torch wali activity se dikhao ki teen tarah ke mirror parallel kirnon ke saath kya karte hain. Chitra ka varnan bhi karo.
Saamaan: torch, kanghi, kaala kaagaz, paper clip, safed kaagaz, plane/concave/convex mirror.
Tareeka: kanghi ke kai daanton ke beech ki jagah khuli rakh kar torch ki roshni se kai patli parallel kirnein banayi. Kirnon ko safed kaagaz pe chalate hue baari-baari plane, concave aur convex mirror pe giraaya aur lauti kirnon ka raasta pencil se banaya.
Observation: plane mirror pe lauti kirnein parallel; concave pe paas aati hain; convex pe phail jaati hain.
Chitra: teen chitra, har ek mein baayin taraf se aati parallel teer wali lines; plane mirror ke baad parallel lines, concave ke baad ek jagah milti lines, convex ke baad phailti lines.
Nishkarsh: concave mirror converge, convex mirror diverge karta hai; har kiran reflection ke niyam maanti hai, curved sateh se normal ki disha badalti hai.
2. Concave mirror dhoop ko kaise ikattha karta hai? Is guna ke teen upyog aur do safety niyam likho.
Concave mirror ki andar mudi sateh pe aayi parallel dhoop ki kirnein reflection ke baad paas aati hain aur focus ke paas ek chhote dot pe ikatthi hoti hain. Bade area ki roshni chhote area pe aane se wahan bahut tez roshni aur garmi hoti hai.
Upyog: (1) dish wala solar cooker, (2) solar concentrator se bhaap aur bijli banana, (3) solar furnace jisme steel tak pighal jaata hai. (Ulta upyog: torch/headlight mein focus pe bulb se parallel beam.)
Safety: (1) Suraj ya mirror mein reflect hoti dhoop ko kabhi seedhe mat dekho. (2) Dot kisi ke chehre/haath pe mat daalo, aur experiment bade ki nigraani mein karo.
📰 Case-Based Question
Rohan ki class ne kanghi aur torch se activity ki. Unke paas teen mirror the jin par sirf X, Y aur Z likha tha. X se lauti kirnein parallel thi, Y se lauti kirnein phail gayi, aur Z se lauti kirnein ek jagah mil gayi. Baad mein teacher ne Z ko dhoop mein rakha aur uske saamne kaagaz aage-peeche karke ek chhota, bahut tez dot banaya.
Q1. X, Y aur Z kaun se mirror hain?
X = plane mirror, Y = convex mirror, Z = concave mirror.
Q2. Z se dhoop ka dot itna chamakdaar aur garam kyun tha?
Z (concave) ne bade area ki dhoop ko chhote dot pe ikattha kar diya, isliye wahan roshni aur garmi bahut zyada thi.
Q3. Teacher ko kaagaz aage-peeche kyun karna pada?
Kirnein focus ke paas sabse achhi tarah milti hain. Kaagaz theek focus ke paas aane pe hi dot sabse chhota aur tez banta hai.
Q4. Kya Y se aayi kirnein reflection ke niyam tod rahi thi? Samjhao.
Nahi. Y ki har kiran ne i = r maana. Convex sateh pe normal har point pe bahar ki taraf alag disha mein hain, isliye kirnein phail gayi.
🚀 HOTS
1. Gaadi ki headlight ka bulb galti se focus se thoda aage khisak jaaye toh beam kaisi hogi?
Tab lauti roshni bilkul parallel nahi rahegi; woh thodi phailegi ya kahin aage jaa kar milegi. Isliye beam door tak saaf nahi jaayegi. Isi wajah se headlight mein bulb ki jagah dhyaan se set ki jaati hai.
2. Do concave mirror ek jaise mude hue hain, par ek bada hai. Kiska dot zyada garam hoga aur kyun?
Bade mirror ka. Mudaav same hone se dot lagbhag same jagah banega, par bada mirror zyada dhoop pakadta hai aur use chhote dot mein ikattha karta hai, toh garmi zyada.
3. Mod pe lage convex mirror se dhoop kisi ki aankh mein chubh sakti hai kya, concave jitni?
Concave jitni nahi. Convex roshni ko phailata hai, toh lauti dhoop halki hoti hai. Phir bhi chamak aa sakti hai, kyunki thodi roshni seedhi aankh tak pahunch sakti hai; par woh ek jagah ikatthi nahi hoti.
🏆 Olympiad Corner
1. Ek chhote concave mirror ki radius 30 cm hai. Dhoop ka sabse chhota dot lagbhag kahan banega? (a) 30 cm (b) 15 cm (c) 60 cm (d) 7.5 cm
✅ (b): f ≈ R ÷ 2 = 30 ÷ 2 = 15 cm.
2. Ek mirror 400 cm² dhoop ko 2 cm² ke dot mein ikattha karta hai. Roshni adhik se adhik kitni guna ghani hogi? (a) 2 (b) 20 (c) 200 (d) 800
✅ (c): 400 ÷ 2 = 200 guna (asal mein thodi roshni kho jaati hai, isliye thoda kam).
3. Ghar ki chhat pe lagi TV dish mein receiver kahan lagaya jaata hai aur kyun?
Dish ke focus pe. Dish concave hoti hai, woh door se aaye (lagbhag parallel) signals ko converge karke focus pe ikattha karti hai, isliye wahan sabse tez signal milta hai.
Har option pe tap karo, turant pata chalega sahi ya galat.
Q1. Same size ke plane, concave aur convex mirror pe sunlight (dhoop: parallel rays) daali. Kaunsa wall pe sabse chhota, bright dot banayega?
(a) Convex
❌ Galat: Convex ko converge karne wala maana. Convex rays ko diverge karta hai: bada, faint (halki) patch.
(b) Plane
❌ Galat: Plane ko ikattha karne wala maana. Plane mirror se rays parallel hi rehti hain: mirror jitna patch.
(c) Concave: rays converge hoke chhoti jagah pe ikatthi
✅ Sahi! Concave mirror parallel rays ko converge karta hai: saari light chhoti jagah pe, isliye dot chhota aur bright.
(d) Teeno same dot banayenge
❌ Galat: Shape ka asar ignore kiya. Concave converge, convex diverge, plane parallel rakhta hai.
Q2. Sun (Suraj) ki rays humare chhote mirror tak lagbhag parallel kyun maani jaati hain?
(a) Sun ki rays hamesha converge hoti hain
❌ Galat: Converge ko Sun ki rays ka gun maana. Converge concave mirror karta hai; door se aayi rays parallel hain.
(b) Mirror rays ko parallel bana deta hai
❌ Galat: Mirror ko reason maana. Rays mirror tak pahunchne se pehle hi lagbhag parallel hain.
(c) Sun chhota hai
❌ Galat: Size ko reason maana. Sun chhota nahi; uski bahut zyada distance se rays parallel aati hain.
(d) Sun bahut door hai, isliye rays lagbhag ek hi direction mein aati hain
✅ Sahi! Sun itna door hai ki chhote mirror tak pahunchne wali rays lagbhag equal distance pe, ek direction mein chalti hain.
Q3. Plane mirror, concave mirror, convex mirror, torch ka reflector: parallel rays daalne pe inme se kitne rays ko converge karenge?
(a) 2
✅ Sahi! Converge sirf concave karta hai: concave mirror (1) + torch ka reflector, jo concave hai (1) = 2.
(b) 1
❌ Galat: Torch ka reflector chhod diya: 1. Woh bhi concave hai: 1 + 1 = 2.
(c) 3
❌ Galat: Convex ko bhi gina: 3. Convex rays ko diverge karta hai: 3 − 1 = 2.
(d) 4
❌ Galat: Sab gin liye (4). Plane parallel rakhta hai, convex diverge karta hai: 4 − 2 = 2.
Q4. Concave mirror se sunlight ko paper pe ek chhote dot pe ikattha kiya. Wahan kya ho sakta hai?
(a) Paper cool ho jaayega
❌ Galat: Ikatthi light ko cooling maana. Chhoti jagah pe zyada energy: heat badhti hai.
(b) Heat badhti hai; der tak rakho to paper burn ho sakta hai
✅ Sahi! Badi area ki light ki energy chhoti jagah pe aa gayi: wahan bahut heat, paper burn ho sakta hai.
(c) Kuch nahi, light mein energy nahi hoti
❌ Galat: Light ki energy bhool gaye. Ikatthi light chhoti jagah pe heat deti hai.
(d) Light spread hokar faint ho jaayegi
❌ Galat: Concave ko diverge wala maana. Concave light ikattha karta hai: bright, hot dot.
Q5. Convex mirror gaadi ke side mirror ke liye kyun useful hai (rays ke hisaab se)?
(a) Woh rays ko converge karta hai
❌ Galat: Concave aur convex ka gun badal diya. Convex diverge karta hai.
(b) Woh rays ko parallel rakhta hai
❌ Galat: Plane mirror ka gun lagaya. Convex rays ko spread karta hai.
(c) Woh rays ko diverge karta hai, isliye bada area dikhata hai
✅ Sahi! Convex surface rays ko spread karti hai (diverge); isi se chhote mirror mein bada area aata hai.
(d) Woh image ko enlarged banata hai
❌ Galat: Concave ka gun lagaya. Convex ka image diminished; fayda zyada area ka hai.
📚 Aur Padho (External Reference)
- NCERT Class 8 Science Curiosity, Chapter 10 (official PDF)
- DIKSHA: Sarkar ka free learning platform, NCERT ke videos ke liye
💖 CharuMam Motivation
Dhoop har jagah girti hai, par kaagaz tabhi jalta hai jab concave mirror us roshni ko ek jagah ikattha karta hai. Bikhri roshni bas halki garmi deti hai; ikatthi roshni aag jala deti hai.
Aapka dhyaan bhi aisa hi hai, beta. Mobile, TV, gappein, sab taraf bikhra dhyaan thoda-thoda kaam karta hai. Par jab aap roz kuch der poora dhyaan ek kaam pe converge karte ho, toh mushkil se mushkil topic bhi pighal jaata hai. Aaj se apne dhyaan ka concave mirror bano. ✨
— CharuMam
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