NCERT Exercise Solutions
Chapter 10 ke saare 12 sawaal: reflection ke niyam, mirror aur lens ki images, aur refraction. Har jawaab kaaran aur diagram ke saath! 🔦✅
🧭 Is Post Mein
📖 Kahani: Chammach mein Ulta Golu!
Shaam ka samay. Golu, Priya aur Rohan chapter 10 ka exercise karne baithe. Table par ek chamakdaar steel ki chammach, ek magnifying glass, aur aadha paani bhara glass ka tumbler rakha tha.
Golu ne chammach ki andar wali (gehri) taraf mein jhaanka aur chillaaya: “Arre! Main toh ulta dikh raha hoon!” Phir chammach palti, toh bahar ubhri taraf mein woh seedha par chhota dikha. “Ek hi chammach, do alag Golu?”
Priya muskurayi: “Andar wali taraf concave mirror hai, bahar wali convex mirror. Isliye image badal gayi.”
Rohan ne tumbler ke peeche pencil rakhi: “Aur dekho, paani ke andar se pencil moti aur toot-ti hui dikh rahi hai! Yeh refraction ka kamaal hai.”
Teeno samajh gaye ki chapter ke saare sawaal kuch chaabiyon se khulte hain: reflection ke niyam, mirror ki images, lens ki images, aur light ka mudna. Aaj inhi chaabiyon se NCERT ke saare 12 sawaal step-by-step solve karenge. 🔑
🎯 Is Post Mein Kya Seekhenge
- Chapter 10 ke end ke saare 12 exercise sawaalon ke poore, kaaran wale jawaab
- Angle of incidence aur angle of reflection normal se naapna, mirror se nahi
- Plane, concave aur convex mirror ki image se mirror pehchaanna
- Convex lens, concave lens aur saade glass ki image mein farq
- Paani bhare glass mein pencil toot-ti kyun dikhti hai (refraction)
🧱 Basics: Pehle Yeh Aana Chahiye
1. Spherical mirror: andar ko mudi chamakdaar satah = concave; bahar ko ubhri = convex. (Post 1: Spherical Mirrors Kya Hain?)
2. Mirror ki images: convex hamesha seedhi aur chhoti; concave paas se seedhi-badi, door se ulti. (Post 2, Post 3)
3. Reflection ke niyam: angle of incidence = angle of reflection, dono normal se naape jaate hain. (Post 4, Post 5)
4. Lens: beech mein mota = convex lens; beech mein patla = concave lens. (Post 6, Post 7)
5. Maths ki taiyaari: Q1 mein 90° − 40° jaisa ghatav aayega. 90 se ghatana aasaan banane ke liye dekho Maths ki Neev MN-11: Ghatana = Kitna aage jaana hai (40 se 90 tak kitna aage? 50!).
💡 Concept: Har Sawaal ki Chaabi
Chapter 10 ke sawaal teen tarah ke hain: angle wale, image pehchaan wale, aur refraction wala. Har ek ki chaabi:
i = r (normal se) | mirror se angle = 90° − i
Sabse badi galti: angle ko mirror ki satah se naap lena. Hamesha normal se naapo!
📘 NCERT Exercise Solutions (Q1–Q12)
Har sawaal ko yahan chhote roop mein apne shabdon mein likha gaya hai. Poora sawaal aur chitra NCERT book ke “Keep the curiosity alive” hisse mein dekho. Jawaab dekhne ke liye click karo, par pehle khud koshish zaroor karna! 💪
Q1 Ek ray mirror par padti hai aur incident ray normal se 40° ka angle banati hai. Reflected ray mirror se kitna angle banayegi? (i) 40° (ii) 50° (iii) 45° (iv) 60°
✅ Option (ii) 50°
Step 1: angle of incidence = 40° (normal se). Niyam se angle of reflection bhi = 40° (normal se).
Step 2: normal aur mirror ke beech 90° hota hai. Isliye reflected ray ka mirror se angle = 90° − 40° = 50°.
- (i) 40° galat: yeh normal se angle hai, mirror se nahi. Sawaal ne mirror se poocha hai.
- (iii) 45° galat: 45° tab hota jab incidence bhi 45° hota.
- (iv) 60° galat: is hisaab se koi 60° nahi banta.
Neeche Diagram 1 mein dono angle (40° aur 50°) dikhaye gaye hain.
Q2 (Chitra par aadharit) Teen case: (i) ray seedhe normal ke saath mirror par padti hai, (ii) mirror tircha hai par ray uske normal ke saath padti hai, (iii) ray normal se 20° par padti hai. Reflected ray kheencho aur angle of reflection batao.
| Case | Angle of incidence | Angle of reflection | Reflected ray kahan jaayegi? |
|---|---|---|---|
| (i) | 0° | 0° | Usi raaste par seedhi wapas laut aayegi |
| (ii) | 0° | 0° | Mirror tircha hai, phir bhi ray uske normal ke saath hai, toh wapas usi raaste par |
| (iii) | 20° | 20° | Normal ke doosri taraf, normal se 20° par |
Kaaran: jo ray normal ke saath aati hai, uska normal se angle 0° hai. i = r, toh r bhi 0°, yaani ray palat kar wahi raasta pakadti hai. Diagram 2 dekho.
Q3 (Chitra par aadharit) Sketch pen ka dhakkan teen mirrors ke saamne rakha hai: plane, convex aur concave. Chitra (i), (ii), (iii) ki images ko sahi mirror se milaao.
Pehchaan ka niyam:
- Image chhoti aur seedhi → convex mirror
- Image ulti, ya bahut paas hone par badi aur seedhi → concave mirror
- Image barabar size ki aur seedhi → plane mirror
Jawaab (book ke chitra ke hisaab se): (i) chhoti-seedhi image → convex; (ii) ulti/badi image → concave; (iii) barabar image → plane.
Tip: exam mein sirf naam mat likho, saath mein kaaran (image ka size aur seedhi/ulti) bhi likho. Isse poore number milte hain.
Q4 (Chitra par aadharit) Wahi dhakkan ek convex lens, ek concave lens aur ek saade flat glass ke peeche barabar doori par rakha hai. Images ko sahi cheez se milaao.
- Image badi dikhe → convex lens (magnifying glass jaisa)
- Image chhoti aur seedhi dikhe → concave lens
- Image bilkul barabar dikhe → flat glass (dono satah seedhi hain, isliye size nahi badalta)
Jawaab kaise likhein: book ke chitra mein jis dhakkan ki image badi hai, uske neeche “convex lens” likho; jo chhoti hai, uske neeche “concave lens”; aur jo barabar hai, uske neeche “flat glass”. Saath mein ek line ka kaaran zaroor likho.
Q5 Jab light mirror par normal ke saath padti hai, toh kaun sa kathan sahi hai? (i) angle of incidence 90° hai (ii) angle of incidence 0° hai (iii) angle of reflection 90° hai (iv) reflection hota hi nahi
✅ Option (ii): angle of incidence 0° hai.
- (i) galat: ray normal ke upar hi hai, toh normal se angle 0° hai. 90° toh mirror ki satah se hai.
- (iii) galat: r = i = 0°, 90° nahi.
- (iv) galat: reflection hota hai; ray usi raaste par wapas laut aati hai (Q2 (i) jaisa).
Q6 (Chitra par aadharit) Teen mirrors (plane, concave, convex) mein ek graph sheet ki image dikh rahi hai. Har mirror ko pehchaan kar uska naam likho.
Graph ke chaukor khaanon ka size dekho:
- Khaane bade dikhe → concave mirror (paas rakhi cheez ko bada dikhata hai)
- Khaane asli jitne → plane mirror
- Khaane chhote aur zyada khaane ek saath dikhe → convex mirror
Jawaab kaise likhein: book ke chitra mein teeno mirrors ke khaanon ka size milaao aur upar ke niyam se har mirror ke upar uska naam likho: sabse bade khaane = concave, asli size = plane, sabse chhote = convex.
Q7 Museum mein ek mahila ek bade convex mirror ki taraf chalti hai. Use kya dikhega? (i) seedhi image lagaataar chhoti hoti jaati hai (ii) ulti image chhoti hoti jaati hai (iii) ulti image badhti hai, phir seedhi aur badi ho jaati hai (iv) seedhi image lagaataar badi hoti jaati hai
✅ Option (iv): seedhi image badi hoti jaati hai.
Kaaran: convex mirror hamesha seedhi aur chhoti image banata hai, isliye (ii) aur (iii) ki “ulti” image ho hi nahi sakti. Jaise-jaise mahila mirror ke paas aati hai, uski image badi hoti jaati hai (phir bhi uske asli size se chhoti hi rehti hai).
- (i) galat: paas aane par image chhoti nahi, badi hoti hai. Door jaane par chhoti hoti.
- (ii) galat: convex mirror kabhi ulti image nahi banata.
- (iii) galat: yeh concave mirror ka vyavhaar hai, convex ka nahi.
Khud check karo: steel ki chammach ki bahar wali ubhri taraf (convex) ko chehre ke paas laao. Chehra seedha rehta hai aur dheere-dheere bada dikhta hai. Kuch guides is sawaal mein (i) likhte hain, par chammach wala test (iv) ko hi sahi saabit karta hai.
Q8 Magnifying glass ko kitaab ke upar rakho, woh doori dhoondo jahan akshar bade dikhein, phir glass ko door le jaao aur badlaav dekho. Magnifying glass kaun sa lens hai?
Magnifying glass ek convex lens hai (beech mein mota, kinaaron par patla).
- Kitaab ke paas: akshar bade aur seedhe dikhte hain.
- Dheere-dheere door le jaane par: akshar aur bade hote hain, phir dhundhle ho jaate hain.
- Aur door le jaane par: akshar ulte aur chhote dikhne lagte hain.
Paas se badi-seedhi aur door se ulti image banana sirf convex lens ka gun hai. Concave lens hamesha chhoti-seedhi image dikhata hai.
Q9 Milaan karo. Column A: (i) concave mirror (ii) convex mirror (iii) convex lens (iv) concave lens. Column B: (a) chamakdaar satah andar ko mudi (b) image hamesha seedhi aur chhoti (c) peeche rakhi cheez kisi doori par ulti dikh sakti hai (d) peeche rakhi cheez hamesha chhoti dikhti hai
| Column A | Column B | Kyun? |
|---|---|---|
| (i) Concave mirror | (a) | “Concave” = guha (cave) jaisa andar ko muda |
| (ii) Convex mirror | (b) | Convex mirror ki image hamesha seedhi aur chhoti |
| (iii) Convex lens | (c) | Door rakhi cheez convex lens se ulti dikhti hai |
| (iv) Concave lens | (d) | Concave lens hamesha chhoti, seedhi image dikhata hai |
Q10 Assertion: Peeche ka traffic dekhne ke liye convex mirror pasand kiya jaata hai. Reason: Convex mirror plane mirror se kaafi bada ilaaka (view) dikhata hai. Sahi option chuno.
✅ Dono kathan sahi hain, aur Reason, Assertion ko sahi samjhata hai.
Convex mirror bahar ko ubhra hota hai, isliye chaaron taraf se aane wali light ko pakad leta hai. Images chhoti ho jaati hain, par bahut saari gaadiyaan ek saath dikh jaati hain. Isi wajah se gaadi ke side mirror mein convex mirror lagta hai.
Bonus: isi chhoti image ki wajah se kai side mirrors par likha hota hai ki cheezein jitni door dikhti hain, asal mein usse paas hoti hain.
Q11 (Chitra par aadharit) Do chitron (a) aur (b) mein O = object, M = mirror, I = image hai. Kaun sa kathan sahi hai? (i) (a) plane, (b) concave (ii) (a) convex, (b) concave (iii) (a) concave, (b) convex (iv) (a) plane, (b) convex
Pehle pehchaan ka tareeka samjho, phir chitra par lagao:
- Plane mirror: I mirror ke peeche, O jitni hi doori par, aur O jitni hi badi aur seedhi.
- Convex mirror: I mirror ke peeche, par mirror ke zyada paas, aur O se chhoti, seedhi.
- Concave mirror: I ulti ho (aksar mirror ke saamne bane), ya O bahut paas ho toh I badi aur seedhi.
Ab chitra par lagao:
| Chitra mein image kaisi hai? | Mirror |
|---|---|
| I mirror ke peeche, O jitni hi door, barabar size | Plane |
| I mirror ke peeche, mirror ke zyada paas, O se chhoti | Convex |
| I ulti, ya O se badi | Concave |
Jis option mein (a) aur (b) dono ka naam is table se mel khaaye, wahi sahi jawaab hai. Jaise: agar (a) mein image barabar doori aur barabar size ki hai aur (b) mein image mirror ke paas aur chhoti hai, toh (a) plane aur (b) convex, yaani option (iv).
Apna jawaab khud parkho: book ke chitra mein ek ruler se O aur I ki mirror se doori naapo aur size milaao. Upar wale teen niyam har aise sawaal ko khol dete hain.
Q12 (Chitra par aadharit) Ek khaali transparent glass tumbler ke peeche pencil rakho. Phir tumbler mein aadha paani bharo. Paani ke paar se pencil kaisi dikhti hai, aur uska aakaar badla hua kyun lagta hai?
Khaali tumbler mein: pencil lagbhag seedhi aur saamaanya dikhti hai.
Aadha paani bharne par: paani ke paar dikhne wala pencil ka hissa mota (bada) aur thoda khiska hua lagta hai. Isliye pencil paani ki satah ke paas tooti hui si dikhti hai: upar ka hissa ek jagah, neeche ka hissa doosri jagah.
Kyun? Light jab hawa se glass aur paani mein, aur phir paani se hawa mein aati hai, toh mud jaati hai. Is mudne ko refraction kehte hain. Gol tumbler + paani milkar ek convex lens jaisa kaam karte hain, isliye peeche ki pencil moti dikhti hai. Hamari aankh maanti hai ki light seedhi aayi, isliye pencil ka woh hissa asli jagah se hata hua dikhta hai.
Aur maza: pencil ko tumbler se thoda door le jaao, toh paani wale hisse mein pencil ki disha ulti (left-right palti) bhi dikh sakti hai, bilkul convex lens ki tarah!
🖼️ Diagrams: Picture se Samjho
🔐 Deep Concept: Exam ke Chhupe Jaal
Yeh hissa sirf charumam.com readers ke liye 🔐
1. Normal ka jaal. Sawaal mein “ray mirror se 30° banati hai” likha ho, toh angle of incidence 30° nahi, 90° − 30° = 60° hai. Pehle hamesha normal se angle nikaalo.
2. “Chhoti” aur “chhoti hoti jaati” ka farq. Convex mirror ki image hamesha object se chhoti hoti hai, lekin paas aane par woh badhti hai. Q7 isi farq ko parakhta hai.
3. Concave mirror aur convex lens jode mein. Dono door se ulti aur paas se badi-seedhi image dete hain. Farq: mirror mein cheez saamne rakhte hain (reflection), lens mein cheez ko lens ke paar dekhte hain (refraction).
4. Convex mirror aur concave lens jode mein. Dono hamesha chhoti aur seedhi image dete hain. Yaad rakhne ki chaabi: “ulte naam, ek kaam”.
5. Normal ke saath ray. i = 0° ka matlab reflection nahi hua, aisa nahi. Reflection hua aur ray wapas usi raaste laut aayi.
6. Refraction vs reflection. Q12 mein pencil ka tootna reflection nahi, refraction hai, kyunki light paani aur glass ke paar ja rahi hai, takra kar laut nahi rahi.
Normal se naapo, i = r | Mirror se angle = 90° − i
Convex mirror + concave lens → hamesha chhota-seedha
Concave mirror + convex lens → door ulta, paas bada-seedha
✏️ Examples: Naye Sawaal, Wahi Chaabi
⚖️ Difference Table: Chapter ke Jode
| Jodi | Pehla | Doosra |
|---|---|---|
| Concave vs Convex mirror | Andar ko muda; door se ulti, paas se badi-seedhi image | Bahar ko ubhra; hamesha chhoti-seedhi image |
| Convex vs Concave lens | Beech mein mota; paas se badi, door se ulti image | Beech mein patla; hamesha chhoti-seedhi image |
| Mirror vs Lens | Light ko lautata hai (reflection) | Light ko paar jaane deta hai aur modta hai (refraction) |
| Angle of incidence vs reflection | Incident ray aur normal ke beech | Reflected ray aur normal ke beech; dono barabar |
| Plane mirror vs Flat glass | Light lautata hai, image peeche dikhti hai | Light paar jaati hai, cheez barabar size ki dikhti hai |
| Reflection vs Refraction | Satah se takra kar laut-na | Ek padarth se doosre mein jaate hue mudna |
🚫 Misconceptions: Log aisa sochte hain… lekin
✅ Hamesha normal se naapte hain. Mirror se angle = 90° − i.
✅ Reflect hoti hai; i = r = 0°, isliye wapas usi raaste laut-ti hai.
✅ Paas jaane par image badhti hai, bas object se chhoti hi rehti hai.
✅ Bahut paas rakhne par woh badi aur seedhi image banata hai (makeup/shaving mirror).
✅ Door le jaane par woh ulti image bhi dikhata hai.
✅ Pencil seedhi hi hai; light mudti hai (refraction), isliye mudi ya tooti dikhti hai.
🔤 Key Terms (Exam mein English shabd hi likhna)
❓ FAQs
Q3, Q4, Q6 mein chitra nahi hai toh kaise likhein?
Pehle niyam likho (jaise “chhoti aur seedhi image convex mirror banata hai”), phir chitra ke label se milaao. Niyam likhne se examiner ko dikhta hai ki aapne kaaran samjha hai.
Q7 mein (i) likhein ya (iv)?
(iv). Convex mirror ki image hamesha seedhi aur chhoti hai, par paas aane par size badhta hai. Steel ki chammach ki ubhri taraf se khud check kar lo.
Q1 mein jawaab 40° kyun nahi?
Kyunki sawaal ne mirror se angle poocha hai. Normal se 40° hai, mirror se 90° − 40° = 50°.
Kya flat glass bhi light ko modta hai?
Haan, thoda khiskata hai, par dono satah seedhi aur barabar hone se cheez ka size nahi badalta. Isliye Q4 mein flat glass ki image barabar size ki hai.
Q12 mein tumbler lens jaisa kaise bana?
Tumbler gol hai, toh paani ka hissa beech mein mota aur kinaaron par patla hua, bilkul convex lens ki tarah. Isliye peeche ki pencil moti dikhti hai.
🧪 Activity: Magnifying Glass ka Jaadu (Q8)
Q8 chapter ki us activity par bana hai jisme convex lens (magnifying glass) ko kitaab se alag-alag doori par rakh kar image ko badalte dekha jaata hai. Yahan use apne shabdon mein step-by-step samjhte hain.
Saamaan: ek magnifying glass (convex lens), ek kitaab ya akhbaar, ek scale (ruler).
👀 Nateeja aur kyun? (Click karo)
| Lens ki doori | Akshar kaise dikhe |
|---|---|
| Kitaab ke bahut paas | Thode bade, seedhe |
| Thoda aur door | Aur bade, seedhe |
| Ek khaas doori ke paar | Dhundhle |
| Kaafi door | Ulte aur chhote |
Is activity se kya seekha? Convex lens paas ki cheez ko bada-seedha dikhata hai aur door ki cheez ki ulti image banata hai. Isliye magnifying glass convex lens 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)
⚠️ Safety Notes
🧠 Think Like a Scientist
🌍 Real Life Mein Chapter 10
- Gaadi ka side mirror aur ghumaavdaar mod ka mirror: convex mirror, bada view ke liye.
- Dentist ka mirror, shaving/makeup mirror: concave mirror, paas se badi-seedhi image.
- Torch aur gaadi ki headlight: bulb ke peeche concave mirror roshni ko ek disha mein bhejta hai.
- Magnifying glass, camera, projector: convex lens.
- Darwaze ka peephole: concave lens jaisa, bahar ka bada hissa chhota karke dikhata hai.
- Talaab mein lakdi tooti dikhna, paani mein sikka upar dikhna: refraction.
🔁 Recap: Poora Chapter Ek Nazar Mein
- Reflection ke niyam: i = r, aur incident ray, reflected ray, normal ek hi plane mein.
- Angle hamesha normal se; mirror se angle = 90° − i. Normal ke saath ray wapas usi raaste.
- Plane mirror: barabar, seedhi image. Convex mirror: hamesha chhoti-seedhi, bada view.
- Concave mirror: door se ulti, bahut paas se badi-seedhi; roshni ikatthi (converge) karta hai.
- Convex lens: beech mein mota; paas se badi-seedhi, door se ulti (magnifying glass).
- Concave lens: beech mein patla; hamesha chhoti-seedhi image. Flat glass: size nahi badalta.
- Refraction: light ka mudna; paani bhare tumbler mein pencil moti aur tooti dikhti hai.
✍️ Fill in the Blanks
1. Angle of incidence aur angle of reflection hamesha ______ se naape jaate hain.
normal
2. Ray normal se 35° par padti hai, toh reflected ray mirror se ______ ka angle banati hai.
55° (90° − 35°)
3. Gaadi ke side mirror mein ______ mirror lagta hai.
convex
4. Magnifying glass ek ______ lens hai.
convex
5. Jo lens hamesha chhoti aur seedhi image dikhata hai, woh ______ lens hai.
concave
6. Light ka ek padarth se doosre mein jaate hue mudna ______ kehlaata hai.
refraction (apvartan)
✅ True / False
1. Normal ke saath padne wali ray ka angle of incidence 90° hota hai.
False: ray normal ke upar hai, toh angle 0° hai.
2. Convex mirror kabhi ulti image nahi banata.
True: uski image hamesha seedhi aur chhoti hoti hai.
3. Concave mirror ke bahut paas rakhi cheez ki image badi aur seedhi hoti hai.
True: isiliye shaving aur dentist ke mirror concave hote hain.
4. Concave lens se door ki cheez ulti dikhti hai.
False: concave lens hamesha chhoti aur seedhi image dikhata hai; ulti image convex lens se dikhti hai.
5. Flat glass ke peeche rakhi cheez barabar size ki dikhti hai.
True: dono satah seedhi hain, isliye size nahi badalta.
6. Paani mein pencil isliye tooti dikhti hai kyunki light paani ki satah se reflect hoti hai.
False: yeh refraction hai; light paani se hawa mein aate hue mudti hai.
🔘 MCQs
Q1. Incident ray mirror ki satah se 60° banati hai. Angle of reflection hai: (a) 60° (b) 30° (c) 120° (d) 90°
✅ (b) 30°: i = 90° − 60° = 30°, aur r = i = 30°.
(a) mirror se angle ko hi i maan liya.
(c) 60° ko dugna kar diya; r normal se naapte hain.
(d) 90° normal aur mirror ke beech ka angle hai, r nahi.
Q2. Incident aur reflected ray ke beech 90° ka angle hai. Angle of incidence hai: (a) 90° (b) 0° (c) 45° (d) 30°
✅ (c) 45°: i + r = 90° aur i = r, toh i = 45°.
(a) poora angle i nahi, i aur r ka jod hai.
(b) i = 0° hota toh dono ray ek hi line par hoti, beech ka angle 0° hota.
(d) 30° + 30° = 60° hota, 90° nahi.
Q3. Kaun sa mirror hamesha chhoti aur seedhi image banata hai? (a) Plane (b) Concave (c) Convex (d) Koi nahi
✅ (c) Convex: bahar ko ubhra mirror hamesha chhoti-seedhi image deta hai.
(a) plane mirror barabar size ki image deta hai.
(b) concave door se ulti aur paas se badi image deta hai.
(d) galat, convex mirror aisa karta hai.
Q4. Dentist daant ko bada dekhne ke liye kaun sa mirror use karta hai? (a) Plane (b) Convex (c) Concave (d) Koi bhi
✅ (c) Concave: paas rakhne par badi aur seedhi image.
(a) plane mirror size nahi badhata.
(b) convex image ko chhota karta hai.
(d) har mirror bada nahi dikhata.
Q5. Kitaab ke akshar ek lens se hamesha chhote dikhte hain, chahe lens kahin bhi rakho. Lens hai: (a) Convex (b) Concave (c) Flat glass (d) Plane mirror
✅ (b) Concave: hamesha chhoti-seedhi image.
(a) convex lens paas se bada dikhata hai.
(c) flat glass barabar size dikhata hai.
(d) mirror ke paar akshar dikhte hi nahi; woh lens nahi.
Q6. Convex lens ko kitaab se kaafi door le jaane par akshar dikhte hain: (a) Bade aur seedhe (b) Ulte (c) Hamesha barabar (d) Gaayab, kabhi nahi dikhte
✅ (b) Ulte: door se convex lens ulti image banata hai.
(a) yeh paas rakhne par hota hai.
(c) convex lens size badalta hai.
(d) dhundhle ho sakte hain, par aur door karne par ulte dikh jaate hain.
Q7. Ek mahila convex mirror se door jaati hai. Uski image: (a) seedhi aur chhoti hoti jaati hai (b) ulti ho jaati hai (c) badi hoti jaati hai (d) barabar rehti hai
✅ (a): convex mirror mein image hamesha seedhi; door jaane par aur chhoti hoti hai.
(b) convex mirror kabhi ulti image nahi banata.
(c) yeh paas aane par hota hai.
(d) barabar image plane mirror ki hoti hai.
Q8. Paani bhare glass mein chammach mudi hui dikhti hai. Kaaran hai: (a) Reflection (b) Refraction (c) Chammach sach mein mud gayi (d) Paani ka rang
✅ (b) Refraction: paani se hawa mein aate hue light mudti hai.
(a) reflection mein light laut-ti hai; yahan light paar aa rahi hai.
(c) chammach bahar nikaalo, seedhi hi hai.
(d) saaf paani mein bhi aisa hota hai, rang ka kaam nahi.
🔗 Assertion–Reason
Options: (a) A aur R dono sahi, 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: Normal ke saath padne wali ray usi raaste par wapas laut aati hai. R: Normal ke saath ray ka angle of incidence 0° hota hai, aur r = i.
✅ (a): i = 0°, toh r = 0°; isliye ray usi line par wapas jaati hai. R seedha A ka kaaran hai.
2. A: Magnifying glass ek convex lens hai. R: Concave lens hamesha chhoti image dikhata hai.
✅ (b): dono sahi hain, par R concave lens ki baat kar raha hai; woh nahi batata ki magnifying glass convex kyun hai (kyunki convex lens paas ki cheez ko bada dikhata hai).
3. A: Shaving mirror convex hota hai. R: Concave mirror paas rakhe chehre ki badi aur seedhi image banata hai.
✅ (d): A galat hai, shaving mirror concave hota hai. R sahi hai, aur wahi batata hai ki shaving mirror concave kyun hota hai.
📝 Very Short Answer (1 mark)
1. Reflection ka pehla niyam kya hai?
Angle of incidence = angle of reflection.
2. Normal aur mirror ke beech kitna angle hota hai?
90°.
3. Torch mein bulb ke peeche kaun sa mirror hota hai?
Concave mirror.
4. Beech mein patla aur kinaaron par mota lens kya kehlaata hai?
Concave lens.
5. Kaun sa mirror sabse bada view (ilaaka) dikhata hai?
Convex mirror.
🗒️ Short Answer (2–3 marks)
1. Concave aur convex mirror ki images mein do farq likho.
(1) Convex mirror hamesha seedhi image banata hai; concave door se ulti aur bahut paas se seedhi. (2) Convex ki image hamesha chhoti; concave ki image paas se badi bhi ho sakti hai.
2. Ek ray normal se 30° par mirror par padti hai. Angle of reflection aur reflected ray ka mirror se angle batao.
Angle of reflection = 30° (i = r). Mirror se angle = 90° − 30° = 60°.
3. Bina chhue kaise bataoge ki koi lens convex hai ya concave?
Lens ko kitaab ke paas rakh kar akshar dekho. Akshar bade dikhein (aur door se ulte) → convex. Hamesha chhote aur seedhe → concave.
4. Gaadiyon mein peeche dekhne ke liye convex mirror kyun lagate hain?
Convex mirror hamesha seedhi image deta hai aur plane mirror se kaafi bada ilaaka dikhata hai, toh driver ek nazar mein peeche ki bahut saari gaadiyaan dekh leta hai.
📄 Long Answer (5 marks)
1. Reflection ke niyam likho. Ek ray normal se 40° par mirror par padti hai: (a) angle of reflection (b) reflected ray ka mirror se angle (c) incident aur reflected ray ke beech ka angle nikaalo. Normal ke saath padne wali ray ka kya hota hai?
Niyam: (1) angle of incidence = angle of reflection; (2) incident ray, reflected ray aur normal ek hi plane mein hote hain.
(a) r = i = 40°.
(b) mirror se angle = 90° − 40° = 50°.
(c) dono ray ke beech = i + r = 40° + 40° = 80°.
Normal ke saath ray: i = 0°, toh r = 0°; ray usi raaste par wapas laut aati hai.
2. Convex aur concave lens ki pehchaan, images aur ek-ek upyog likho. Q12 jaisa paani bhara gol tumbler kaun sa lens ban jaata hai aur kyun?
Convex lens: beech mein mota; paas rakhi cheez badi-seedhi, door ki cheez ulti dikhti hai. Upyog: magnifying glass, camera, projector.
Concave lens: beech mein patla; image hamesha chhoti aur seedhi. Upyog: darwaze ka peephole jaisa, door ki nazar ke chashme.
Tumbler: paani bhara gol tumbler beech mein mota aur kinaaron par patla hota hai, isliye convex lens jaisa kaam karta hai. Light paani aur glass se guzarte hue mudti (refraction) hai, isliye peeche ki pencil moti aur khiski hui dikhti hai.
📰 Case-Based Question
(i) Scooter ka side mirror kaun sa mirror hai, aur kyun?
Convex mirror; hamesha seedhi, chhoti image aur bada view deta hai.
(ii) Funny mirror mein shakal kyun badal jaati hai?
Uski satah kahin andar ko mudi (concave jaisi) aur kahin bahar ko ubhri (convex jaisi) hoti hai, toh alag hisse alag size ki image banate hain.
(iii) Dadi ke chashme mein kaun sa lens hai?
Convex lens, kyunki paas ke akshar bade dikh rahe the.
(iv) Chammach tooti hui kyun dikhi?
Refraction: chammach ke paani wale hisse se aane wali light paani se hawa mein aate hue mud jaati hai, toh woh hissa khiska hua dikhta hai.
🚀 HOTS (Higher Order Thinking)
1. Do plane mirror aapas mein 90° par jude hain. Ek ray pehle mirror par normal se 30° par padti hai. Doosre mirror par uska angle of incidence kitna hoga?
Pehle mirror se reflected ray, pehle mirror se 90° − 30° = 60° banati hai. Do mirror aur ray ek triangle banate hain jiske kon 90°, 60° aur 30° hain, toh ray doosre mirror se 30° banati hai. Doosre mirror par angle of incidence = 90° − 30° = 60°.
2. Pahaadi sadak ke tikhe mod par convex mirror lagate hain, concave nahi. Concave lagaya toh kya dikkat hogi?
Door se aati gaadi concave mirror mein ulti dikhegi aur view bhi chhota hoga, toh driver ko samajhne mein der lagegi. Convex mirror hamesha seedhi image aur bada view deta hai, isliye mod ke doosri taraf ki gaadi jaldi dikhti hai.
3. Aapke paas teen ek jaise dikhne wale goal kaanch ke tukde hain. Sirf ek akhbaar se kaise pehchaanoge ki kaun convex lens hai, kaun concave aur kaun saada glass?
Har tukde ko akhbaar ke thoda upar rakh kar dekho. Akshar bade dikhein → convex lens. Chhote dikhein → concave lens. Bilkul barabar dikhein → saada flat glass. Pakka karne ke liye convex wale ko door le jaao: akshar ulte dikhne chahiye.
🏆 Olympiad Corner
1. Incident ray aur reflected ray ke beech 110° ka angle hai. Reflected ray ka mirror se angle hai: (a) 55° (b) 35° (c) 110° (d) 70°
✅ (b) 35°: i + r = 110°, i = r = 55°; mirror se angle = 90° − 55° = 35°.
(a) yeh angle of reflection hai (normal se), mirror se nahi.
(c) yeh dono ray ke beech ka angle hai.
(d) 180° − 110° kar diya; yeh mirror ke saath dono taraf ke kon ka jod hai (35° + 35°).
2. Plane mirror ko 10° ghumaane par (ray wahi rahe), reflected ray kitna ghoomti hai? (a) 10° (b) 5° (c) 20° (d) 0°
✅ (c) 20°: mirror 10° ghooma toh normal bhi 10° ghooma; i mein 10° ka badlaav aur r mein bhi 10° ka, toh reflected ray kul 2 × 10° = 20° ghoomti hai.
(a) sirf normal ka ghoomna gina.
(b) aadha kar diya, ulta hisaab.
(d) mirror ghoomne par ray zaroor badalti hai.
3. Inme se kaun si jodi “hamesha chhoti aur seedhi image” deti hai? (a) Concave mirror aur convex lens (b) Convex mirror aur concave lens (c) Plane mirror aur flat glass (d) Concave mirror aur concave lens
✅ (b): convex mirror aur concave lens dono hamesha chhoti-seedhi image dete hain.
(a) yeh dono paas se badi, door se ulti image dete hain.
(c) yeh dono size nahi badalte, barabar image.
(d) concave mirror ulti ya badi image bhi deta hai.
Har option pe tap karo, turant pata chalega sahi ya galat.
Q1. Incident ray aur reflected ray ke beech 100° ka angle hai. Reflected ray mirror ki surface se kitna angle banati hai?
(a) 50°
❌ Galat: Normal se angle de diya: 100 ÷ 2 = 50. Surface se: 90° − 50° = 40°.
(b) 40°
✅ Sahi! Angle of incidence = angle of reflection = 100 ÷ 2 = 50° (normal se). Surface se: 90° − 50° = 40°.
(c) 100°
❌ Galat: Dono rays ke beech wala angle hi de diya: 100. Pehle 100 ÷ 2 = 50, phir 90° − 50° = 40°.
(d) 80°
❌ Galat: 180° se subtract kiya: 180 − 100 = 80. Normal se 50°, surface se 90° − 50° = 40°.
Q2. Ek mirror mein graph sheet ke squares asli se chhote, aur ek saath zyada squares dikhe. Mirror kaunsa hai?
(a) Concave
❌ Galat: Concave ko chhota dikhane wala maana. Paas rakhi sheet ke squares concave mein bade dikhte hain.
(b) Plane
❌ Galat: Plane ko chhota dikhane wala maana. Plane mein squares asli size ke dikhte hain.
(c) Convex
✅ Sahi! Convex mirror image chhota karta hai aur zyada area dikhata hai: chhote aur zyada squares.
(d) Mirror nahi, yeh lens hai
❌ Galat: Mirror ko lens maana. Image mirror mein dikhi; squares ka size dekh ke mirror pehchaano.
Q3. Convex lens, concave lens aur flat glass ke peeche same distance pe pen ka cap rakha. Jisme cap bilkul same size dikha, woh kya hai?
(a) Convex lens
❌ Galat: Convex ko same size wala maana. Convex lens cap ko bada dikhata hai.
(b) Concave lens
❌ Galat: Concave ko same size wala maana. Concave lens cap ko chhota dikhata hai.
(c) Plane mirror
❌ Galat: Glass ko mirror maana. Cap glass ke peeche hai; light guzarti hai, lautti nahi.
(d) Flat glass: dono surfaces flat hain
✅ Sahi! Flat glass light ko lens ki tarah nahi modta, isliye size same rehta hai.
Q4. Half water bhare glass tumbler ke peeche pencil moti aur tooti hui si dikhti hai. Kyun?
(a) Refraction: light water aur air ke beech mudti hai, aur round tumbler convex lens jaisa hai
✅ Sahi! Light water se air mein aate waqt mudti hai (refraction). Round tumbler + water convex lens jaisa: pencil moti dikhti hai.
(b) Reflection: water pencil ko wapas dikhata hai
❌ Galat: Reflection ko reason maana. Light water ke through aati hai aur mudti hai: refraction.
(c) Pencil sach mein moti ho gayi
❌ Galat: Image ko asli change maana. Pencil wahi hai; light ke mudne se moti dikhti hai.
(d) Tumbler concave lens jaisa hai
❌ Galat: Tumbler ko concave maana. Round tumbler + water convex lens jaisa hai: pencil moti dikhti hai.
Q5. Ray mirror pe normal ke saath girti hai. Incident ray aur mirror ki surface ke beech kitna angle hai?
(a) 0°
❌ Galat: Normal se angle de diya: 0. Surface se poocha: 90° − 0° = 90°.
(b) 90°
✅ Sahi! Normal ke saath matlab angle of incidence 0°. Normal surface se 90° pe: 90° − 0° = 90°.
(c) 45°
❌ Galat: Half kar diya: 90 ÷ 2 = 45. Ray normal ke saath hai: surface se 90° − 0° = 90°.
(d) 180°
❌ Galat: Do baar 90° add kar diya: 90 + 90 = 180. Surface se angle: 90° − 0° = 90°.
📚 Aur Padho (External Reference)
- NCERT Class 8 Science Curiosity, Chapter 10 (official PDF): chapter ke end mein “Keep the curiosity alive” wale poore sawaal aur chitra dekho
- DIKSHA: Sarkar ka free learning platform, NCERT ke videos ke liye
💖 CharuMam Motivation
Badhai ho! Aapne poora Chapter 10 khatam kar liya. 🎉 Yaad hai chammach? Ek hi chammach mein Golu kabhi ulta dikha, kabhi seedha, kabhi bada, kabhi chhota. Golu wahi tha, bas mirror badal gaya tha.
Zindagi mein bhi log aur halaat alag-alag “mirror” jaise hote hain: koi aapko chhota dikhayega, koi bada. Par yaad rakho, asli aap wahi ho jo mirror ke saamne khade ho, image nahi. Aur reflection ka niyam bhi yaad rakho: jaisa angle se aap duniya ko roshni doge, waisi hi laut kar aayegi. Aaj kisi dost ko chammach wala experiment dikhao aur use Q7 samjhao! 🌱
— CharuMam
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