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ScienceCh 10 Human Eye aur Rangeen Duniya

The Human Eye and the Colourful World (Human Eye aur Rangeen Duniya): Class 10 Science Chapter 10 Hinglish mein

Science · Hinglish notes, simulations aur practice · Official NCERT chapter PDF ↗

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  • 70 min
  • 20 practice questions
  • 26 MCQs

Is chapter mein aap kya seekhenge

  • Human eye ke parts ke naam batao aur samjhao ki woh retina par real, inverted image kaise banate hain
  • Accommodation samjhao, aur normal eye ka near point aur far point batao
  • Myopia, hypermetropia aur presbyopia, unke causes aur unka correction ray diagrams ke saath samjhao
  • Diye gaye far point ya near point ko correct karne wale lens ki focal length aur power calculate karo
  • Glass prism se ek ray trace karo aur angle of incidence, emergence aur deviation pehchano
  • Dispersion, spectrum, Newton ka colours ko dobara milana aur rainbow ka banna samjhao
  • Atmospheric refraction se taaron ka twinkle karna aur advance sunrise aur delayed sunset samjhao
  • Scattering se Tyndall effect, aasmaan ka blue colour aur red danger signals ka use samjhao

NCERT Science Class 10, Chapter 10, pp. 161–170 par based original companion text. Yeh NCERT se juda nahi hai aur NCERT ne ise endorse nahi kiya hai.

Bus aage badh rahi hai aur tum uska number padhte ho, phir haath mein pakde ticket par nazar daalte ho. Pal bhar mein dono saaf dikhte hain, aur iske liye tumne kuch nahi kiya. Yeh kaam tumhari aankhon ne kiya. Pichhle chapter mein tum lenses aur unki banayi images se mile the. Yahan tum dekhoge ki har aankh mein apna ek adjustable lens hota hai, aur spectacles bas extra lenses hain jo uski madad karte hain.

Chapter ka doosra hissa bahar ki duniya ko dekhta hai. Glass, baarish ki boondon aur khud hawa se guzarti light kuch roz ke ajoobe dikhati hai: prism se nikalti rangon ki patti, geeli highway ke upar rainbow, timtimaate taare, thoda pehle ugta Sun aur blue aasmaan. Har ek ki wajah hai jo tum refraction aur scattering se samjha sakte ho.

10.1 Human Eye

Socho ki tum aankhein band karke sari ya cricket jersey chun rahe ho. Chhookar pata chal jaata hai ki kapda soft hai, lekin yeh koi nahi batata ki woh maroon hai ya navy blue. Door ki cheezon ka colour aur detail humein sirf dekhne se milta hai, isiliye aankh hamare sabse keemti sense organs mein se ek hai.

Aankh ko ek zinda camera samjho jo lagbhag 2.3 cm chaudi ek ball mein band hai. Kuch parts light ko focus karte hain, kuch control karte hain ki kitni light andar aaye, aur ek part picture ko brain ke liye signals mein badalta hai. Har part se milte hue Fig. 10.1 ko follow karo.

4/4Object ke har point se aane wali rays retina par milti hain: image real aur inverted hoti hai.

Fig. 10.1Aankh ke parts. Simple rakhne ke liye saari bending lens par dikhayi gayi hai; asli aankh mein zyadatar bending cornea karta hai.NCERT Fig. 10.1 · p. 161

Ek eyeball ka side view, jismein light left se aa rahi hai. Step 1 aage ke parts label karta hai: saaf, ubhra hua cornea, rangeen iris aur pupil, jo iris ke beech ka gap hai. Step 2 iris ke theek peeche eye lens aur use upar-neeche se pakadne wali ciliary muscles label karta hai. Step 3 retina, yaani peeche ki curved parat, aur aankh ke peeche se brain ki taraf jaati optic nerve label karta hai. Step 4 left mein object ke roop mein ek seedha khada arrow jodta hai; uski tip se rays pupil aur lens se guzar kar retina par milti hain, jahan ek chhota, ulta arrow image dikhata hai.

Focusing do parts mil kar karte hain. Pehla hai cornea (स्वच्छ मंडल), sabse aage ka saaf dome, ghadi ke glass jaisa. Light cornea mein ghuste waqt sabse zyada mudti hai, isliye zyadatar focusing cornea hi karta hai. Doosra hai crystalline eye lens, thoda andar ek saaf, jelly jaisa lens. Yeh thodi si, adjustable bending jodta hai, bas utni jitni paas ya door ki cheezon ko sharp karne ke liye chahiye.

Do parts light control karte hain. Iris woh rangeen ring hai jo tum kisi ki aankhon mein dekhte ho; yeh muscle ka bana hota hai. Uske centre ka dark circle, pupil, bas ek chhed hai. Kam light mein iris pupil ko bada karta hai aur tez light mein chhota, jisse aankh ka pichhla hissa chakachaundh se bachta hai.

Ek part sense karta hai, ek report karta hai. Cornea aur lens mil kar retina (दृष्टिपटल) par, yaani peeche ki parat par, ek real, inverted image banate hain. Retina mein laakhon light-sensitive cells hote hain. Light unhe on karti hai aur woh chhote-chhote electrical signals bhejte hain. Optic nerve, nerve fibres ki ek cable, in signals ko brain tak le jaati hai, jo unhe woh seedha scene samajhta hai jo tum dekhte ho.

Definition
Retina

Aankh ke peeche ki light-sensitive layer jis par image banti hai. Iske cells light ko electrical signals mein badalte hain.

ExampleIs page ki image abhi tumhare retina par ulti ban rahi hai.

Table 10.1Aankh ke parts aur har part ka kaam
PartIska kaamCamera mein kya
CorneaSaaf front window; light ki zyadatar bending karta haiLens ka front glass
IrisRangeen muscle ring jo pupil ka size control karti haiAperture ring
PupilOpening jo light andar aane deti haiAperture
Eye lensPaas aur door ki cheezon ke liye focus ko fine-tune karta haiFocusing lens
Ciliary musclesEye lens ki curvature badalti hainFocus ring
RetinaLight-sensitive screen jahan image banti haiSensor ya film
Optic nerveRetina se signals brain tak le jaati haiScreen tak jaati cable
Quick check
3 mein se 1
Aankh ke har part ko uske kaam se match karo.

Left mein koi item tap karo, phir right mein uska match.

Answer dekho
Answer
  • Cornea : zyadatar bending karta hai
  • Iris : pupil ka size control karta hai
  • Retina : light ko signals mein badalta hai
  • Optic nerve : signals brain tak le jaati hai
Cornea light ko modta hai, iris opening adjust karta hai, retina sense karta hai aur optic nerve message le jaati hai.

10.1.1 Power of Accommodation

Camera apne lens ko sensor ke paas ya door karke focus karta hai. Tumhari aankh aisa nahi kar sakti: eye lens se retina tak ki doori fixed rehti hai. Iske bajaay aankh apne lens ki shape badalti hai, aur uske saath focal length bhi.

Paas ke object se rays aankh tak tezi se phailti hui aati hain, isliye unhe chhoti focal length wala strong lens chahiye. Iske liye lens ke chaaron taraf ki ciliary muscles (पक्ष्माभी पेशियाँ) kas jaati hain; soft lens phool jaata hai, uski curvature badhti hai aur focal length ghat jaati hai. Door ke object se rays lagbhag parallel aati hain aur unhe sirf weak lens chahiye. Tab muscles dheeli pad jaati hain, lens kheench kar patla ho jaata hai, aur uski focal length tab tak badhti hai jab tak parallel rays theek retina par na milein. Dono cases dekhne ke liye Fig. 10.2 ke steps chalao.

3/3Muscles contract hoti hain, lens mota hota hai, focal length chhoti hoti hai: phir se sharp.

Fig. 10.2Accommodation: aankh apne lens ki focal length badalti hai, apni length nahi. Ray paths bani hui distances ke liye lens formula follow karte hain.

Ek simple aankh, jismein lens aage aur curved retina peeche hai, aur lens ke upar-neeche ciliary muscles hain. Step 1 mein door ke object se parallel rays patle lens se guzar kar retina par milti hain; label kehta hai ki ciliary muscles relaxed hain. Step 2 mein left ke paas wale object se rays phailti hain; wahi patla lens unhe time par ikattha nahi kar paata, isliye woh retina par blurred patch ki tarah padti hain aur uske peeche milti, jo dashed lines se dikhaya gaya hai. Step 3 mein ciliary muscles contract ho chuki hain, lens do guna mota bana hai, aur paas ke object ki rays ab retina par milti hain.

Definition
Power of accommodation

Aankh ki apne lens ki focal length badalne ki capacity, taaki paas aur door dono objects ki retina par sharp images banein.

ExampleNotebook se nazar utha kar blackboard dekhte hi tumhari aankhein second ke ek hisse mein refocus kar leti hain.

Accommodation ki limits hain. Lens ek had tak hi phool sakta hai, isliye uski focal length ki ek sabse chhoti value hoti hai. Ek sui ko naak ke lagbhag chhoote hue pakdo aur uska ched dekhne ki koshish karo: tum nahi dekh paoge, aur aankhein jaldi thak jaayengi. Sabse kam doori jahan tum bina strain ke aaram se padh sakte ho, use near point kehte hain. Iska doosra naam least distance of distinct vision hai. Healthy aankhon wale young adult ka near point lagbhag 25 cm hota hai.

Doosri taraf, far point woh sabse zyada doori hai jahan tak aankh ab bhi saaf dekh sakti hai. Normal eye ke liye yeh infinity par hai: aankh muscles ko poora relaxed rakh kar door ki pahadi ya Moon par focus kar sakti hai. Isliye normal eye lagbhag 25 cm se infinity tak sab kuch saaf dekhti hai.

Definition
Near point (least distance of distinct vision)

Sabse paas ka point jahan aankh bina strain ke object ko saaf dekh sakti hai; healthy young eye ke liye lagbhag 25 cm.

Definition
Far point

Sabse door ka point jahan aankh object ko saaf dekh sakti hai. Normal eye ke liye yeh infinity par hai.

Quick check
4 mein se 1
Tum phone se nazar utha kar aasmaan mein bahut upar udti patang ko dekhte ho. Tumhari aankh ke andar kya hota hai?
Answer dekho

Answer (C) Ciliary muscles relax hoti hain aur lens patla ho jaata hai, uski focal length lambi ho jaati hai

Door ke object ke liye ciliary muscles relax hoti hain, lens chapta ho jaata hai aur uski focal length badh jaati hai. Muscles ka contract hona paas ke objects ke liye hai, aur retina kabhi nahi hilta.

10.2 Defects of Vision aur Unka Correction

Apni class mein chaaron taraf dekho: tumhare kai dost shayad spectacles pehente hain. Unki aankhein image ko theek retina par nahi la paati, isliye bina madad ke duniya ka kuch hissa blurred dikhta hai. Aksar iski wajah eyeball ki shape ya aankh ki focusing power hoti hai, aur aisi problems ko refractive defects kehte hain. Sabse common teen hain: myopia, hypermetropia aur presbyopia. Har ek ko sahi kind aur power ke spherical lenses se correct kiya ja sakta hai, aur spectacles yahi hote hain.

Myopia (near-sightedness)

Myopic eye mein door ke objects ke liye focusing bahut strong hoti hai. Door ki kisi hoarding se aane wali parallel rays retina tak pahunchne se pehle hi focus ho jaati hain, phir cross karke phail jaati hain, isliye retina par point ki jagah ek blurred patch banta hai. Paas ke object se rays phailti hui aati hain aur phir bhi theek se focus hoti hain. Isliye myopia (निकट-दृष्टि दोष) wala vyakti aasaani se padh leta hai lekin board, road signs ya outfield mein ball dekhne mein dikkat hoti hai. Uska far point infinity se khisak kar shayad do-teen metre par aa jaata hai, kabhi-kabhi isse bhi kaafi kam.

Extra focusing ki do aam wajah hoti hain. Eye lens jitna hona chahiye usse zyada curved ho sakta hai, ya eyeball aage se peeche tak zyada lamba ho gaya ho sakta hai, jisse retina focus point ke peeche aa jaata hai.

Iska ilaaj hai sahi power ka concave lens. Yeh door ke object ki parallel rays ko aise phailata hai ki woh vyakti ke far point se aati lagti hain. Aankh apne far point par rakhe objects ko pehle se focus kar sakti hai, isliye image phir se retina par aa jaati hai. Fig. 10.3 dekho.

3/3Concave lens rays ko aise phailata hai jaise woh far point se aa rahi hon: sharp.

Fig. 10.3Myopia aur uska correction. Concave lens door ke objects ko aisa dikhata hai jaise woh aankh ke far point par hon.NCERT Fig. 10.2 · p. 163

Ek simple aankh, jismein dashed principal axis hai. Step 1 mein aankh ke kuch aage, is aankh ke far point ke roop mein marked point se aane wali rays theek retina par milti hain, jahan sharp likha hai. Step 2 mein door se aane wali parallel rays retina ke aage milti hain, cross karti hain, aur retina par blurred patch ki tarah pahunchti hain. Step 3 mein aankh ke aage ek concave spectacle lens rakha gaya hai; yeh parallel rays ko aise phailata hai ki unke dashed back-extensions far point par milte hain, aur phir aankh unhe retina par sharp focus karti hai.

Definition
Myopia (near-sightedness)

Ek defect jismein door ke objects blurred dikhte hain kyunki unki image retina ke aage banti hai. Ise concave lens se correct karte hain.

Myopia ke liye lens
f=−xF,P=−1xF
(10.1)
jahan
xF
vyakti ke far point ki doori (P dioptres mein ho to metres mein)
f
concave spectacle lens ki focal length

(10.1) kahan se aata hai? Infinity par rakhe object (u=−∞) ki virtual image far point par (v=−xF) banni chahiye. Tab lens formula 1/f=−1/xF deta hai. Hum spectacle lens ko aankh se chhoota hua maante hain, jo spectacles ke liye kaafi sahi hai.

Example 10.1

Myopic student ke liye spectacles

Kabir apni notebook aasaani se padh leta hai, lekin 40 cm se door ki har cheez blurred dikhti hai. Use kaun sa lens chahiye, aur uski focal length aur power kya hai?

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Hypermetropia (far-sightedness)

Hypermetropia (दीर्घ-दृष्टि दोष) ulti problem hai: aankh ki focusing bahut weak hoti hai. Door ke objects ke liye aankh ciliary muscles se kaam lekar phir bhi sambhal leti hai, isliye door ki cheezein saaf dikhti hain. Lekin paas pakdi kitaab se rays zyada tezi se phailti hain, aur sabse zyada curved lens bhi unhe time par ikattha nahi kar paata; woh retina ke peeche milti. Near point 25 cm se kaafi aage khisak jaata hai. Is problem wali bachchi apni kitaab door pakad sakti hai aur padhne ke baad use sir dard ho sakta hai.

Focusing weak kyun hoti hai? Ya to eyeball bahut chhota hai, jisse retina lens ke bahut paas hai, ya eye lens ki focal length bahut lambi hai.

Ilaaj hai aankh ke aage kuch converging power lagana: ek convex lens. Yeh 25 cm par rakhi kitaab ki rays ko aise modta hai ki woh vyakti ke apne near point se aati lagti hain, jahan aankh sambhal leti hai. Fig. 10.4 ke teen steps compare karo.

3/3Convex lens rays ko aisa banata hai jaise woh N se aa rahi hon: sharp.

Fig. 10.4Hypermetropia aur uska correction. Convex lens 25 cm par rakhe object ko aisa dikhata hai jaise woh aankh ke apne near point N par ho.NCERT Fig. 10.3 · p. 163

Ek simple aankh, jiske aage axis par do points marked hain: N, is aankh ka near point, kaafi left mein, aur N prime, 25 cm par normal near point, aankh ke zyada paas. Step 1 mein N se rays retina par milti hain, jahan sharp likha hai. Step 2 mein N prime se rays milne se pehle retina se takrati hain aur blurred patch banati hain, aur dashed lines dikhati hain ki woh retina ke peeche milti. Step 3 mein aankh ke aage ek convex spectacle lens rakha gaya hai; N prime se rays isse guzar kar aise chalti hain jaise N se aa rahi hon, jo dashed back-extensions se dikhaya gaya hai, aur retina par sharp milti hain.

Definition
Hypermetropia (far-sightedness)

Ek defect jismein paas ke objects blurred dikhte hain kyunki unki image retina ke peeche banti; near point 25 cm se door hota hai. Ise convex lens se correct karte hain.

Hypermetropia ke liye lens
1f=1d−1xN
(10.2)
jahan
d
normal near point, 25 cm, jahan hum padhna chahte hain
xN
vyakti ki aankh ka near point
f
convex spectacle lens ki focal length

(10.2) lens formula se aata hai, jismein kitaab u=−d par aur uski virtual image v=−xN par hai. Kyunki xN, d se bada hai, focal length positive aati hai: yaani convex lens.

Example 10.2

Far-sighted dukaandaar ke liye reading glasses

Ek dukaandaar ko apni account book padhne ke liye use aankhon se 75 cm door pakadna padta hai. Kaun sa lens use 25 cm ki normal doori par padhne dega? Uski focal length aur power nikaalo.

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Presbyopia

Jaise-jaise log bade hote hain, ciliary muscles kamzor ho jaati hain aur eye lens sakht ho jaata hai. Power of accommodation ghat jaati hai, aur near point dheere-dheere door khisakta hai. Chaalees se upar ke kai logon ko lagta hai ki phone padhne ke liye use door pakadna padta hai. Umar se jude is defect ko presbyopia (जरा-दूरदृष्टिता) kehte hain. Convex lenses wale reading glasses madad karte hain.

Kuch logon ko dono taraf madad chahiye: door ki cheezein blur hoti hain aur paas ka print bhi. Unke spectacles do zones mein bante hain, door ke liye upar concave zone aur padhne ke liye neeche convex zone. Aise lenses ko bifocals kehte hain. Pehenne wala bas upar ya neeche sahi zone se dekhta hai, jaise Fig. 10.5 mein.

2/2Neeche convex part se dekhne par kitaab focus mein aati hai.

Fig. 10.5Bifocal lens: glass ka ek tukda, do powers.

Right mein ek aankh bifocal spectacle lens se dekh rahi hai. Lens ka upar ka part concave lens jaisa aur neeche ka part convex lens jaisa hai. Step 1 mein aankh upar dekhti hai aur ek dashed line of sight upar ke concave part se door ki pahadiyon ki taraf jaati hai. Step 2 mein aankh neeche mud gayi hai aur line of sight neeche ke convex part se ek khuli kitaab tak jaati hai.

Definition
Presbyopia

Budhape ka ek defect jismein near point door khisak jaata hai kyunki ciliary muscles kamzor ho jaati hain aur eye lens ki flexibility kam ho jaati hai. Ise convex lenses se correct karte hain.

Aaj refractive defects ko contact lenses se bhi correct kiya ja sakta hai, jo seedhe cornea par baithte hain, ya laser surgery se jo cornea ki shape badal deti hai. Eye doctor check karta hai ki kis vyakti ke liye kaun sa option sahi hai.

Table 10.3Teen common defects ek saath
DefectSaaf nahi dikhtaImage kahan banti haiAam wajahCorrection
Myopiadoor ke objectsretina ke aagelens zyada curved ya eyeball zyada lambaconcave lens
Hypermetropiapaas ke objectsretina ke peechefocal length zyada lambi ya eyeball zyada chhotaconvex lens
Presbyopiapaas ke objects (umar ke saath)retina ke peechekamzor ciliary muscles, sakht lensconvex lens (dono hon to bifocals)
InteractiveEye clinic

Side se bani ek model aankh, jismein rays left se andar aati hain. Buttons se normal, myopic, hypermetropic ya budhape wali aankh chuni jaati hai, aur quick buttons object ko 25 cm par kitaab, 2 m par dost ya door ki pahadi par le jaate hain. Ek slider object ko khiskata hai aur doosra minus 4 se plus 4 dioptres tak ka spectacle lens jodta hai, jo concave ya convex lens ke roop mein dikhta hai. Ciliary muscles ke kaam karne par eye lens mota hota hai, aur aankh ke andar rays ya to retina par milti hain ya uske aage ya peeche chook jaati hain, jo blurred patch ki tarah dikhta hai. Cards eye lens ki power, ciliary muscles ki state, spectacle power aur image kahan banti hai, yeh batate hain, aur ek sentence samjhata hai ki kya ho raha hai.

Fig. 10.6Ek aankh chuno, object ko khiskao, aur spectacle lenses try karo jab tak image retina par na aa jaaye.
Quick check
4 mein se 1
Riya apni kitaab aasaani se padh leti hai, lekin sadak ke us paar bus ka number blurred dikhta hai. Use kaun sa defect hai, aur use kaise correct karte hain?
Answer dekho

Answer (C) Myopia, concave lens se

Paas saaf hai, door blurred: yeh myopia hai. Door ki bus ki image retina ke aage banti hai, aur concave lens use peeche le jaata hai. Convex lens ise aur bigaad deta.
Practice · 4 questions

Practice 10.1 (NCERT ke in-text questions, p. 164): answers ke saath

  1. Short answerEasyNCERT in-text Questions p. 164, Q1

    Jab aankh 'accommodate' karti hai, to woh kya karti hai? Kaun si muscles ise possible banati hain?

    Solution dikhao

    AnswerYeh paas aur door ke objects ke hisaab se apne lens ki focal length badalti hai; yeh kaam ciliary muscles karti hain.

    Eye lens apni curvature, aur isliye apni focal length, badal sakta hai, taaki paas aur door ki cheezein retina par sharp focus hon. Is capacity ko power of accommodation kehte hain. Door ke objects ke liye ciliary muscles relax hokar lens ko patla karti hain aur paas ke objects ke liye contract hokar use mota karti hain.

  2. Short answerEasyNCERT in-text Questions p. 164, Q2

    Ek dukaandaar price tags aasaani se padh leta hai, lekin use sirf lagbhag 2 m tak saaf dikhta hai; saamne ki door wali deewar par ghadi blurred hai. Use kis type ka lens chahiye? (Bonus: kitni power?)

    Solution dikhao

    AnswerPower −0.5 D wala concave lens.

    Use myopia hai: uska far point 2 m hai. Concave lens ise correct karta hai. (10.1) se, P=−1/(2 m), yaani −0.5 D.

  3. Short answerEasyNCERT in-text Questions p. 164, Q3

    Normal young eye ka near point aur far point batao. Aisi aankh kitni doori ki range mein saaf dekh sakti hai?

    Solution dikhao

    AnswerNear point lagbhag 25 cm, far point infinity par; yeh 25 cm se infinity tak saaf dekhti hai.

    Near point (least distance of distinct vision) lagbhag 25 cm hai. Far point infinity par hai. Isliye aankh lagbhag 25 cm se infinity tak kahin bhi saaf dekhti hai.

  4. Short answerMediumNCERT in-text Questions p. 164, Q4

    School match mein stands ki pichhli row mein baithi ek ladki scoreboard nahi padh paati, jabki apni notebook aasaani se padh leti hai. Use kaun sa defect ho sakta hai, aur use kaise correct kiya ja sakta hai?

    Solution dikhao

    AnswerMyopia; sahi power ke concave lenses se correct hota hai.

    Use paas ki cheezein saaf dikhti hain lekin door ki nahi, isliye shayad use myopia (near-sightedness) hai. Scoreboard ki image uske retina ke aage banti hai. Eye test ke baad diye gaye sahi power ke concave lenses wale spectacles ise correct kar denge.

10.3 Prism se Light ka Refraction

Aankh ke paas glass prism pakad kar usmein se darwaaze ki frame dekho. Frame ek taraf khisak gayi lagti hai, yaani prism apne andar se guzarti light ko mod raha hai. Rectangular glass slab aisa nahi karta. Uske dono faces parallel hote hain, isliye doosre face ka bend pehle face ke bend ko cancel kar deta hai, aur ray bas side mein khisakti hai.

Triangular prism alag hai. Iske do triangular ends aur teen rectangular side faces hote hain. Light ek side face se andar jaati hai aur doosre se bahar nikalti hai, aur yeh dono faces ek doosre ki taraf jhuke hote hain. Inke beech ke angle ko angle of the prism kehte hain; common equilateral prism ke liye yeh 60° hota hai. Neeche wali activity mein ek prism se ray trace karo.

Fig. 10.7 path ko step by step dikhata hai. Ray do baar mudti hai, dono baar base ki taraf, isliye bends cancel hone ke bajaay jud jaate hain. Incident ray ki direction aur emergent ray ki direction ke beech ke angle ko angle of deviation (विचलन कोण), D, kehte hain. Apni activity mein ise naapo.

4/4Dono bends ray ko base ki taraf modte hain. Kul mudaav angle of deviation D hai.

Fig. 10.7Prism se refraction, jo refractive index 1.5 wale glass, 60° prism aur 50° ke angle of incidence ke liye Snell's law se banaya gaya hai (r ≈ 31°, e ≈ 47°, D ≈ 37°).NCERT Fig. 10.4 · p. 166

Ek triangular glass prism jiska nukeela corner upar hai, aur us par angle of the prism A marked hai. Step 1 mein ek incident ray neeche left se upar uthti hai aur left face se milti hai; normal dashed hai aur angle of incidence i marked hai. Step 2 mein refracted ray glass ko lagbhag horizontal paar karti hai, normal ki taraf mudi hui, aur angle r marked hai. Step 3 mein emergent ray right face se normal se door mud kar nikalti hai, neeche right ki taraf jaati hai, aur angle e marked hai. Step 4 mein incident ray ko dashed line se aage aur emergent ray ko peeche badhaya gaya hai; unke beech ka angle D, yaani angle of deviation, marked hai.

Definition
Angle of deviation

Jab light prism se guzarti hai, to incident ray ki direction aur emergent ray ki direction ke beech ka angle.

Quick check
3 mein se 1
Prism ke pehle face par light air se glass mein jaati hai. Woh kaise mudti hai?
Answer dekho

Answer (A) Normal ki taraf

Air se denser medium mein jaate hue light dheemi hoti hai aur normal ki taraf mudti hai. Normal se door woh sirf glass se nikalte waqt mudti hai.

10.4 Glass Prism se White Light ka Dispersion

Mirror ya jhoomar ke cut-glass edge par padti dhoop kabhi-kabhi deewar par rangon ke chhote-chhote dhabbe bana deti hai. Phir bhi dhoop khud colourless dikhti hai. Yeh colours aate kahan se hain? Prism se hum yeh pata kar sakte hain.

Tum jo dekhte ho woh spectrum (स्पेक्ट्रम) hai: white light rangon ki ek patti mein khul gayi. Inhe paramparik roop se saat naam diye jaate hain: ek end par violet, indigo aur blue, beech mein green aur yellow, aur doosre end par orange aur red. Inke pehle letters, VIBGYOR, order yaad rakhne mein madad karte hain. Asal mein colours ek doosre mein smoothly mil jaate hain, isliye agar tumhe indigo aur blue ke beech koi saaf edge na mile to chinta mat karo. White light ke is tarah rangon mein khulne ko dispersion (विक्षेपण) kehte hain.

Iski wajah glass mein hai. Violet light glass mein red light se thoda dheere chalti hai, isliye violet ke liye glass ka refractive index thoda zyada hota hai. Isliye violet sabse bade angle se mudta hai aur red sabse chhote se, aur baaki colours beech mein. Screen tak pahunchte-pahunchte colours ek ke bagal ek phail jaate hain, jaise Fig. 10.8 dikhata hai.

3/3Screen par: ek spectrum, red (sabse kam muda) se violet (sabse zyada muda) tak.

Fig. 10.8Prism se dispersion. Har colour Snell's law se trace kiya gaya hai, lekin colours ke beech ka phailaav badha kar dikhaya gaya hai taaki bands dikh sakein.NCERT Fig. 10.5 · p. 167

White light ki ek patli beam left mein ek card ki slit se guzar kar glass prism mein jaati hai. Step 1 mein sirf prism tak pahunchti white beam dikhti hai, aur right mein khaali screen hai. Step 2 mein prism ke andar light thodi si colours mein phailti hai. Step 3 mein colours prism se nikal kar ek chaude fan mein phailte hain jo screen par saat bands ki tarah padte hain, jin par upar se R, O, Y, G, B, I, V likha hai. Labels batate hain ki red sabse kam aur violet sabse zyada mudta hai.

Definition
Dispersion

White light ka un colours mein phailna jinse woh bani hai, kyunki har colour alag angle se mudta hai.

Definition
Spectrum

Rangon ki patti, violet se red tak (VIBGYOR), jo white light ke disperse hone par milti hai.

Newton ke do prisms

Kya colours prism banata hai, ya woh shuru se dhoop mein the? Newton ka jawab do aur tests se aaya. Ek mein, unhone ek colour ko chhod kar poora spectrum rok diya aur us colour ko ek doosre prism se bheja. Woh phir se muda lekin bilkul usi colour ka raha: prism naye colours nahi bana sakta. Doosre mein, unhone ek waisa hi doosra prism ulta karke pehle ke paas rakha. Doosre prism ne phailaav ko ulat diya, colours mil gaye, aur ek white beam bahar aayi. Fig. 10.9 ke steps chalao.

3/3Ulta prism saare colours ko ikattha kar deta hai: phir se white light.

Fig. 10.9Newton ka test: prism un colours ko alag karta hai jo white light mein pehle se hain. Ray paths Snell's law se trace kiye gaye hain; phailaav badha kar dikhaya gaya hai.NCERT Fig. 10.6 · p. 167

Step 1 mein white light left ke prism mein jaati hai aur colours ke fan mein phail kar screen par rangon ki patti ki tarah padti hai. Step 2 mein slit wala ek card sirf green hissa aage jaane deta hai; yeh ek doosre, chhote prism se guzarta hai, aur mudta hai lekin green hi rehta hai. Step 3 mein ek doosra prism, bilkul waisa lekin ulta, pehle ke theek bagal mein rakha hai; colours usmein se guzar kar original direction mein chalti white light ki ek beam ke roop mein saath bahar aate hain.

To dhoop colours ka mixture hai, aur prism bas unhe alag-alag karta hai. Garam filament ya white LED ki light, jo isi tarah rangon ki poori patti mein khulti hai, use bhi white light kehte hain.

Rainbow

Monsoon ki baarish ke baad, agar tumhare peeche Sun nikal aaye aur aage abhi baarish ho rahi ho, to tumhe rainbow dikh sakta hai: laakhon boondon dwara aasmaan mein phailaya gaya spectrum. Yeh hamesha aasmaan mein Sun ke opposite side par hota hai, kabhi uski taraf nahi.

Fig. 10.10 mein dhoop ki ek ray ko boond ke andar follow karo. Curved surface mein ghuste waqt yeh refract hoti hai, aur kyunki paani bhi glass ki tarah violet ko red se zyada modta hai, yeh tootne lagti hai. Yeh boond ko paar karke peeche ki surface se milti hai, jahan yeh boond ke andar reflect hoti hai. Nikalte waqt yeh ek baar aur refract hoti hai, jisse colours aur door-door phail jaate hain. Light Sun ki side ki taraf wapas nikalti hai, isiliye Sun tumhare peeche hona chahiye. Har boond red ko violet se thode zyada steep angle par bhejti hai, isliye red tum tak upar ki boondon se aata hai aur violet neeche ki boondon se.

4/4Light Sun ki side ki taraf wapas aati hai: rainbow tab dikhta hai jab Sun tumhare peeche ho.

Fig. 10.10Baarish ki boond dhoop ko kaise todti hai: refraction, internal reflection aur phir refraction. Snell's law se trace kiya gaya; colours ke beech ka phailaav badha kar dikhaya gaya hai.NCERT Fig. 10.8 · p. 167

Ek badi gol baarish ki boond, jiske right mein Sun aur aati hui white dhoop ki ek ray hai. Step 1 mein ray boond ke upar right hisse mein ghusti hai, mudti hai aur colours ke ek patle fan mein toot kar boond ke peeche ki taraf jaati hai. Step 2 mein colours peeche ki surface se reflect hokar boond ke neeche ki taraf jaate hain. Step 3 mein woh boond ke neeche se nikalte hain, phir mudte hain aur red se violet tak ek fan mein phail kar neeche right ki taraf jaate hain. Step 4 mein neeche right ki ek aankh light leti hai, jis par likha hai ki yeh tumhari aankh hai aur Sun tumhare peeche hai.

Quick check
4 mein se 1
In colours ko prism se sabse kam mudne wale se sabse zyada mudne wale ke order mein lagao.
  1. Red
  2. Blue
  3. Violet
  4. Yellow
  5. Green
Answer dekho
Answer
  1. Red
  2. Yellow
  3. Green
  4. Blue
  5. Violet
Red sabse kam aur violet sabse zyada mudta hai; order VIBGYOR ko ulta padhne jaisa hai.

10.5 Atmospheric Refraction

Garam tandoor ke upar se, ya May ki dopahar mein highway ke saath door dekho, to us paar ki cheezein kaanpti si lagti hain. Garam hawa thandi hawa se patli hoti hai, aur patli hawa light ko thoda kam modti hai: uska refractive index thoda kam hota hai. Tandoor ke upar garam aur thandi hawa ke pockets lagataar upar uthte aur ek doosre ke paas se ghoomte rehte hain, isliye bending badalti rehti hai. Inke beech se jo bhi dikhta hai, woh kaanpta sa lagta hai.

Badalte refractive index wali hawa dwara light ke mudne ko atmospheric refraction (वायुमंडलीय अपवर्तन) kehte hain. Tandoor ke upar yeh lagbhag ek metre mein hota hai. Taaron aur Sun ki light ke liye yeh hamare upar ki saikdon kilometre hawa mein hota hai.

Taaron ka twinkle karna

Hawa zameen ke paas sabse dense hoti hai aur upar jaate-jaate patli hoti jaati hai, isliye uska refractive index upar ki taraf dheere-dheere ghatta hai. Isliye atmosphere mein ghusne wali taaron ki light neeche tak patli se dense hawa mein jaati rehti hai. Yeh normal ki taraf mudti rehti hai, isliye uska path halka sa curve ho jaata hai, jaise Fig. 10.11 mein.

Tumhari aankh taare ko us direction mein dekhti hai jahan se light aakhir mein aati hai. Woh direction asli direction se zyada steep hoti hai, isliye taara jitna hai usse thoda upar dikhta hai. Horizon ke paas wale taaron ke liye yeh effect sabse zyada hota hai.

3/4Peeche trace karne par light taare se upar ke point se aati lagti hai.

Fig. 10.11Taare ki light dense hawa mein jaate hue mudti hai, isliye taara jitna hai usse upar dikhta hai. Layers aur bending badha kar dikhayi gayi hain.NCERT Fig. 10.9 · p. 168

Zameen ke upar hawa ki horizontal patiyaan bani hain, upar halki (patli hawa) aur zameen ke paas gehre rang ki (dense hawa), aur unke upar khaali jagah hai. Upar right mein ek taara hai aur neeche left mein ek vyakti khada hai. Step 1 mein sirf layers, taara aur vyakti dikhte hain. Step 2 mein taare se ek ray neeche vyakti tak aati hai, har boundary par vertical normal ki taraf mudti hai, jisse uska path aur steep hota jaata hai. Step 3 mein ek dashed line ray ke aakhri hisse ko peeche upar ek dashed taare tak badhati hai, jis par seen here likha hai, jo asli taare se aasmaan mein upar hai; ek dotted line asli direction dikhati hai. Step 4 mein dikhne wali position ke paas do halke extra taare dikhate hain ki apparent position khisakti rehti hai.

Ab hawa jodo. Garam aur thandi hawa ke cells lagataar line of sight ke aar-paar behte rehte hain, tandoor ke upar ke bhanwar ki tarah, aur har ek taare ki light ko thoda dhakka deta hai. Taara itna door hai ki uski light ek single point se rays ki ek bahut patli pencil ki tarah hum tak aati hai. Ek dhakka us pencil ka bada hissa tumhare pupil se hata sakta hai, aur agla use wapas la sakta hai. Isliye taare ki brightness second mein kai baar timtimaati hai aur uski position thodi kaanpti hai. Yahi timtimaana twinkling hai.

Planet ki kahani alag hai. Yeh itna paas hai ki uski light ek chhoti si disc se aati hai, yaani ek extended source se, bhale hi aankh ko yeh point jaisa dikhe (telescope disc ko saaf dikhata hai). Disc ke ek edge aur doosre edge se aane wali light thodi alag hawa se guzarti hai. Jab disc ka ek hissa dhundhla hota hai, doosra chamak jaata hai, aur tumhari aankh tak pahunchne wali kul light mushkil se badalti hai. Isliye Venus, Jupiter aur Mars steady light se chamakte hain.

Compare

Taare twinkle kyun karte hain aur planets kyun nahi

Taara

  • Bahut door
  • Point source ki tarah kaam karta hai
  • Ek patli beam, jise chalti hawa aasaani se khiska deti hai
  • Brightness timtimaati hai: twinkle karta hai

Planet

  • Kaafi paas
  • Extended source ki tarah kaam karta hai (ek chhoti disc)
  • Kai beams; unki timtimaahat average ho jaati hai
  • Steady light: twinkle nahi karta

Advance sunrise aur delayed sunset

Astronomers sunrise ka time us pal ko maante hain jab Sun ki disc sach mein horizon paar karti hai. Tumhe woh thoda pehle dikh jaata hai. Jab Sun abhi horizon ke theek neeche hota hai, uski light dense se aur dense hawa mein jaate hue curve hoti hai, Earth ki golaai ke upar mud kar tumhari aankh tak pahunchti hai. Tumhe Sun us direction mein dikhta hai jahan se woh light aati hai, jo horizon ke theek upar hai.

Subah lagbhag 2 minutes ka fayda hota hai, aur shaam ko yahi ulta hota hai: Sun sach mein doobne ke baad bhi lagbhag 2 minutes dikhta rehta hai. Dono milkar har din kuch minutes ki roshni jod dete hain. Isi effect se horizon ke paas Sun ki disc thodi chapti dikhti hai. Uske neeche ke edge ki light zyada hawa se guzarti hai aur upar ke edge ki light se zyada upar uthti hai. Fig. 10.12 dekho.

3/4Sun asal mein ugne se lagbhag 2 minutes pehle tumhe horizon ke upar dikhta hai.

Fig. 10.12Advance sunrise: hawa dhoop ko horizon ke upar mod deti hai. Ray ko aisi hawa mein trace kiya gaya hai jiska refractive index upar jaate hue ghatta hai; bending badha kar dikhayi gayi hai (asal mein lagbhag aadha degree).NCERT Fig. 10.10 · p. 168

Curved Earth ki surface ka close-up, samundar ki tarah dikhaya gaya, uske upar hawa ki ek halki patti aur uske paar space. Left mein kinaare par ek aankh right ki taraf dashed horizon line ke saath dekhti hai. Step 1 mein Sun right mein horizon line ke neeche bana hai; aankh se Sun tak ek dotted seedhi line samundar mein ghus jaati hai aur us par cross laga hai. Step 2 mein Sun se ek curved ray hawa mein mud kar aankh tak pahunchti hai. Step 3 mein ek dashed line aati hui direction ko horizon ke upar Sun ki dashed outline tak badhati hai, jis par seen here likha hai, jabki asli Sun par really here likha hai. Step 4 mein dikhne wala Sun dab kar oval ho jaata hai, jis par chapta dikhta likha hai.

Quick check
4 mein se 1
Taara twinkle kyun karta hai?
Answer dekho

Answer (D) Badalte refractive index wali chalti hawa uski light ko khiskaati rehti hai

Lagataar badalti hawa mein atmospheric refraction point jaise taare ki patli beam ko bhatkaata hai, isliye uski brightness timtimaati hai. Taara khud steady chamakta hai.

10.6 Scattering of Light

Yaad hai Class 9 mein namak wale paani aur doodhiya paani mein torch chamkaayi thi? Salt solution mein beam side se nahi dikhti thi; colloid mein, jiske particles kaafi bade hote hain, woh chamakte raaste ki tarah dikhti thi. Yahi simple observation nature ke kuch sabse sundar colours ki chaabi hai: saaf aasmaan ka blue, gehre samundar ke paani ka blue aur subah-shaam ka laal Sun.

10.6.1 Tyndall Effect

Jab light kisi bahut chhote particle se milti hai, to particle us light ka kuch hissa har direction mein bhej deta hai. Ise scattering (प्रकीर्णन) kehte hain. Hamare aas-paas ki hawa scatterers se bhari hai: uske apne molecules, aur dhool aur dhuein ke kan aur paani ki chhoti boondein. Beam ke particles se scatter hui light ka kuch hissa side mein, tumhari aankhon mein jaata hai, isliye tum dekh paate ho ki beam kahan se ja rahi hai.

2/3Agarbatti ke dhuein ke saath beam ka raasta chamak uthta hai.

Fig. 10.13Tyndall effect: particles light ko side mein scatter karte hain, isliye beam dikh jaati hai.

Ek andhera kamra jiske upar left mein ek torch lagi hai. Uski beam tirchhi neeche farsh par ek chamakte patch tak jaati hai, aur right mein ek aankh kamre ko side se dekhti hai. Step 1 mein hawa saaf hai: beam ka raasta sirf halki dashed lines se dikhaya gaya hai aur us par path not seen likha hai. Step 2 mein agarbatti se dhuaan uthta hai aur beam kanon wali ek chamakti yellow patti ki tarah chamakti hai, jis par beam chamakti likha hai. Step 3 mein ek magnified circle beam ke do particles dikhata hai, har ek har direction mein chhote blue arrows bhejta hai, jis par light goes every way likha hai.

Particles dwara light ki scattering, jisse beam ka raasta dikh jaata hai, Tyndall effect (टिंडल प्रभाव) hai. Tum ise cinema projector ki beam mein, sardi ki dhundh bhari raat mein car ki headlights mein, aur dhool bhare kamre mein torch ki beam mein dekhte ho, jaise Fig. 10.13 mein.

Definition
Tyndall effect

Chhote particles (jaise colloid, dhuaan ya dhundh mein) dwara light ki beam ki scattering, jisse beam ka raasta dikh jaata hai.

Particle ka size matter karta hai. Particle jitna chhota, woh utna hi blue ko, yaani spectrum ke short-wavelength end ko, zyada scatter karta hai. Bade particles lambi wavelengths ko bhi scatter karte hain, aur baadal ki boondon jitne bade particles har colour ko lagbhag barabar scatter karte hain, isliye unki scattered light white hoti hai. Isiliye baadal white dikhte hain jabki unke aas-paas ka saaf aasmaan blue hota hai.

10.6.2 Saaf Aasmaan ka Colour Blue Kyun Hota Hai?

Sun se door aasmaan ko dekho: woh chamakta hai, jabki Sun wahan nahi hai. Yeh chamak woh dhoop hai jise hawa khud tumhari taraf scatter karti hai. Air molecules light ki wavelength se bahut chhote hote hain, aur itne chhote scatterers choosy hote hain. Woh short wavelengths ko lambi wavelengths se kahin zyada scatter karte hain, isliye blue, jiski wavelength red ki aadhi se thodi zyada hai, kahin zyada strongly scatter hota hai.Red light ki wavelength blue ki lagbhag 1.8 guna hai. Wavelength se bahut chhote scatterers ke liye iska matlab hai ki blue, red se lagbhag das guna zyada strongly scatter hota hai.

To jab dhoop atmosphere ko paar karti hai, uska blue hissa poore aasmaan mein bikhar jaata hai, jabki zyadatar red, orange aur yellow seedha aage nikal jaate hain. Sun se door tum jahan bhi dekho, tum tak pahunchne wali light zyadatar yahi scattered blue hoti hai. Fig. 10.14 follow karo.

3/4Scattered blue light poore aasmaan se tum tak pahunchti hai.

Fig. 10.14Aasmaan blue kyun hai: chhote air molecules blue light ko red se kahin zyada scatter karte hain.

Upar left mein Sun hai aur zameen ke upar molecules ke dots wali hawa ki ek patti hai. Zameen par ek vyakti khada hai. Step 1 mein dhoop ki ek seedhi beam hawa ko paar karti hai. Step 2 mein beam par teen molecules har direction mein chhote blue arrows bhejte hain, jis par blue scattered the most likha hai, jabki ek red arrow beam ke saath aage jaata hai, jis par red, orange aage likha hai. Step 3 mein upar ke molecules se blue arrows vyakti tak pahunchte hain aur hawa blue rang ki ho jaati hai, jis par aasmaan blue likha hai. Step 4 mein hawa gayab hai, molecules mit jaate hain aur vyakti ke upar taaron wala ek grey dome hai, jis par aasmaan kaala, no air, no scattering likha hai.

Hawa hata do aur blue bhi chala jaata hai. Moon par hawa nahi hai, aur wahan li gayi photos mein Sun kaale aasmaan mein dhadhakta dikhta hai. Bahut upar udte jet se bhi upar ka aasmaan zyada gehra, dark blue dikhta hai, kyunki ab hawa ka bada hissa tumhare neeche hai.

Scattering se yeh bhi samajh aata hai ki danger signals red kyun hote hain. Dhundh, dhuaan aur dhool red light ko sabse kam scatter karte hain. Isliye red tail-light, mobile tower ke upar ki red light ya red railway signal dhundh mein door se bhi chamakdaar aur red dikhte hain, jab baaki colours fade ho jaate.

Quick check
4 mein se 1
Saaf aasmaan blue kyun dikhta hai?
Answer dekho

Answer (D) Air molecules blue light ko red light se kahin zyada scatter karte hain

Air molecules light ki wavelength se chhote hote hain aur short wavelengths (blue) ko sabse zyada scatter karte hain. Samundar wali baat ek aam myth hai: samundar se bahut door bhi aasmaan blue hota hai.
Recap

Summary aur key points

  1. Aankh retina par real, inverted image banati hai. Zyadatar bending cornea karta hai, eye lens use fine-tune karta hai, aur optic nerve signals brain tak le jaati hai (Section 10.1).
  2. Ciliary muscles eye lens ki curvature, aur isliye uski focal length, badalti hain. Yeh power of accommodation ek hi aankh ko paas aur door ke objects par focus karne deti hai (Section 10.1.1).
  3. Normal eye apne near point (lagbhag 25 cm, least distance of distinct vision) se infinity par apne far point tak saaf dekhti hai (Section 10.1.1).
  4. Myopia: door ke objects blur hote hain kyunki unki image retina ke aage banti hai; concave lens se correct hota hai, P=−1/xF (Myopia (near-sightedness)).
  5. Hypermetropia: paas ke objects blur hote hain kyunki unki image retina ke peeche banti; convex lens se correct hota hai (Hypermetropia (far-sightedness)).
  6. Presbyopia: umar ke saath near point door khisakta hai; convex lenses se correct hota hai, ya bifocals se agar door dekhne ke liye concave lens bhi chahiye (Presbyopia).
  7. Prism light ko do baar modta hai, dono baar apne base ki taraf; kul mudaav angle of deviation hai (Section 10.3).
  8. Prism white light ko spectrum (VIBGYOR) mein disperse karta hai kyunki har colour alag amount se mudta hai: red sabse kam, violet sabse zyada (Section 10.4).
  9. Rainbow baarish ki boondon mein refraction aur dispersion, internal reflection aur phir refraction se banta hai, Sun ke opposite side (Rainbow).
  10. Atmospheric refraction se taare twinkle karte hain (planets nahi) aur hum Sun ko sunrise se lagbhag 2 minutes pehle aur sunset ke baad tak dekh paate hain (Section 10.5).
  11. Chhote particles light ko scatter karte hain (Tyndall effect); air molecules blue ko sabse zyada scatter karte hain, isliye saaf aasmaan blue hai, aur red signals dhundh mein sabse door tak jaate hain (Section 10.6).
Practice · 16 questions

Practice questions answers ke saath (NCERT “Exercises”)

  1. Quick answerEasyNCERT Exercises Q1

    Meera apni kitaab se nazar utha kar sadak ke us paar ek hoarding dekhti hai, aur woh lagbhag turant focus mein aa jaati hai. Aankh ki kaun si capacity ise possible banati hai?

    Answer dekho

    Answer (C) Accommodation

    Accommodation, yaani eye lens ka apni focal length badalna, aankh ko paas se door refocus karne deta hai. Myopia aur presbyopia defects hain; dispersion prisms ke baare mein hai.
  2. Quick answerEasyNCERT Exercises Q2

    Jab tum door ki dukaan ke sign par naam padhte ho, to uski sharp image tumhari aankh ke kis part par banti hai?

    Answer dekho

    Answer (B) Retina

    Image retina par banti hai, jo peeche ki light-sensitive layer hai. Cornea light ko modta hai, aur iris aur pupil control karte hain ki kitni light andar aaye.
  3. Quick answerEasyNCERT Exercises Q3

    Healthy young adult eye mein least distance of distinct vision lagbhag cm hoti hai.

    Answer dekho

    Answer 25

    Lagbhag 25 cm; yeh normal young eye ka near point hai.
  4. Quick answerEasyNCERT Exercises Q4

    Aankh ka kaun sa part eye lens ki focal length badalta hai?

    Answer dekho

    Answer (D) Ciliary muscles

    Ciliary muscles lens ki curvature badalti hain. Iris sirf pupil ka size badalta hai.
  5. NumericalMediumNCERT Exercises Q5

    Optometrist ne Mr Rao ke prescription mein likha hai: distance vision −4.0 D, near vision +2.5 D.

    1. Distance vision wale lens ki focal length nikaalo.

      Solution dikhao

      Answer−25 cm (concave)

      f=1/P, isliye f=1/(−4.0 D), jo −0.25 m ya −25 cm hai. Minus sign ka matlab hai concave (diverging) lens.

    2. Near vision wale lens ki focal length nikaalo.

      Solution dikhao

      Answer+40 cm (convex)

      f=1/(+2.5 D), jo +0.40 m ya +40 cm hai: ek convex (converging) lens. Aise vyakti ko bifocals ki salaah di jaayegi.

  6. NumericalMediumNCERT Exercises Q6

    Ek myopic student ko apni aankhon se sirf 60 cm tak saaf dikhta hai. Use chahiye wale lens ka nature aur power nikaalo.

    Solution dikhao

    AnswerLagbhag −1.7 D power wala concave lens (f=−60 cm).

    Door ke object ke liye u=−∞ hai aur image far point par, v=−60 cm par, banni chahiye.

    1f=−160 cm

    Isliye f=−0.60 m, ek concave lens, aur P=1/f, lagbhag −1.67 D.

  7. DiagramHardNCERT Exercises Q7

    Hypermetropia aur uska correction.

    1. Ek labelled ray diagram banao jo dikhaye ki convex lens hypermetropia ko kaise correct karta hai.

      Solution dikhao

      AnswerFig. 10.4, step 3 dekho.

      Aankh banao, jismein defective eye ka near point N kaafi aage ho aur normal near point N′ (25 cm) zyada paas. Aankh ke aage ek convex lens banao. N′ par rakhe object se rays lens se guzar kar aise nikalti hain jaise N se aa rahi hon (dashed back-extensions), aur aankh unhe retina par focus karti hai. N, N′, convex lens aur retina ko label karo, jaise Fig. 10.4 mein.

    2. Ek hypermetropic vyakti ka near point 80 cm par hai. Kitni power ka lens use 25 cm par padhne dega?

      D
      Solution dikhao

      Answer+2.75 D

      u=−25 cm (kitaab) aur v=−80 cm (near point par uski virtual image) lo.

      1f=−180+125
      1f=11400 cm−1

      Isliye f≈36.4 cm, yaani 0.364 m, aur P=+2.75 D: ek convex lens.

  8. Short answerMediumNCERT Exercises Q8

    Apne phone ko aankhon se sirf 10 cm door pakdo, aur kitni bhi koshish karo, text blur ho jaata hai. Samjhao ki yahan aankh ko kya rokta hai, aur normal eye ke liye lagbhag 25 cm sabse kam aaram wali doori kyun hai.

    Solution dikhao

    AnswerEye lens itna curved nahi ho sakta (uski focal length itni chhoti nahi ho sakti) ki itne paas ke objects ko retina par focus kar sake.

    Kisi paas ke object ko fixed retina par focus karne ke liye eye lens ko chhoti focal length chahiye, isliye ciliary muscles ko use zyada curved karna padta hai. Lens kitna phool sakta hai, iski ek limit hai. Lagbhag 25 cm se paas ke objects ke liye sabse curved lens bhi rays ko retina par ikattha nahi kar paata; woh uske peeche milti, isliye image blurred hoti hai aur aankh par strain padta hai.

  9. Short answerMediumNCERT Exercises Q9

    Ek bus lambi sadak par tumse door jaati hai aur tum use dekhte rehte ho. Kya tumhare eye lens aur bus ki image ke beech ki doori badalti hai? Agar nahi, to kya badalta hai?

    Solution dikhao

    AnswerImage distance same rehti hai; eye lens ki focal length badhti hai.

    Image hamesha retina par banti hai, aur eye lens se retina ki doori nahi badalti, isliye image distance same rehti hai. Jaise-jaise bus door jaati hai, ciliary muscles relax hoti hain, lens patla hota hai aur uski focal length badhti hai, jisse image retina par hi rehti hai.

  10. Short answerMediumNCERT Exercises Q10

    Sardi ki saaf raat mein horizon ke paas neeche ke taare timtimaate aur brightness badalte lagte hain. Yeh twinkling kis wajah se hoti hai?

    Solution dikhao

    AnswerChalti hawa mein atmospheric refraction point jaise taare ki light ko khiskaata rehta hai, isliye uski brightness timtimaati hai.

    Taare ki light hawa ki un layers se guzarte hue lagataar refract hoti hai jinka refractive index zameen ki taraf badhta hai, isliye taara jitna hai usse thoda upar dikhta hai. Hawa chalti rehti hai aur uska refractive index badalta rehta hai, isliye light ka path aur taare ki apparent position thodi-thodi khisakti rehti hai. Taara itna door hai ki woh point source hai, isliye aankh mein jaane wali uski light ki amount badalti rehti hai: taara kabhi zyada chamakdaar, kabhi dhundhla dikhta hai. Yahi twinkling hai.

  11. Short answerMediumNCERT Exercises Q11

    Shaam ke aasmaan mein neeche Venus steady light se chamakta hai jabki uske paas ke taare twinkle karte hain. Planet ki light ko steady kya banata hai?

    Solution dikhao

    AnswerPlanet extended source hai; uske kai points ki timtimaahat average ho jaati hai.

    Planet kisi bhi taare se kahin zyada paas hai, isliye woh ek chhoti disc ki tarah dikhta hai: ek extended source. Hum planet ko kai point sources ka group maan sakte hain. Har point ki light atmospheric refraction ki wajah se timtimaati hai, lekin changes random hote hain, isliye kisi bhi pal aankh tak pahunchne wali kul light lagbhag same rehti hai. Timtimaahat average ho jaati hai aur planet twinkle nahi karta.

  12. Short answerMediumNCERT Exercises Q12

    International Space Station par astronauts ki li gayi photos mein Sun chamakte hue bhi aasmaan kaala dikhta hai. Samjhao ki unka aasmaan blue ke bajaay kaala kyun hai.

    Solution dikhao

    AnswerItni oonchai par dhoop ko scatter karne ke liye lagbhag koi hawa nahi hai, isliye unhe koi scattered blue light nahi milti.

    Aasmaan humein blue dikhta hai kyunki hawa ke molecules dhoop ke blue hisse ko har direction mein scatter karte hain. Spacecraft ki oonchai par lagbhag koi atmosphere nahi hai, isliye mushkil se koi light scatter hoti hai. Astronauts tak sirf Sun (ya Earth) se seedhi aane wali light pahunchti hai; baaki aasmaan se koi light nahi aati, isliye woh kaala dikhta hai.

  13. Quick answerMedium

    Assertion (A): Oonchi buildings aur mobile towers par danger lights red hoti hain. Reason (R): Dhundh, dhuaan aur dhool red light ko sabse kam scatter karte hain. Sahi option chuno.

    Answer dekho

    Answer (A) A aur R dono sahi hain, aur R, A ki sahi explanation hai

    Dono sahi hain, aur R, A ko samjhata hai: kyunki red sabse kam scatter hota hai, red light dhundh mein lambi doori tak apni brightness aur colour banaye rakhti hai.
  14. Short answerHard

    Case study. Ek eye clinic chaar patients record karta hai. P (16 years) ko sirf 1.5 m tak saaf dikhta hai. Q (12 years) 1.25 m se paas aaram se nahi padh paata lekin door ke objects achchhe se dekhta hai. R (62 years) door ke objects achchhe se dekhta hai lekin use akhbaar haath ki poori lambai par pakadna padta hai. S (58 years) na door ke objects saaf dekh paata hai aur na paas se padh paata hai.

    1. P ke defect ka naam batao aur P ko chahiye wale lens ki power nikaalo.

      D
      Solution dikhao

      AnswerMyopia; −0.67 D (concave)

      P ko 1.5 m se aage nahi dikhta: yeh myopia hai, jiska far point 1.5 m hai. xF=1.5 m ke saath P=−1/xF use karne par P≈−0.67 D milta hai, ek concave lens.

    2. Q ko 25 cm par padhne ke liye chahiye wale lens ki power nikaalo.

      D
      Solution dikhao

      Answer+3.2 D (convex)

      Q ko hypermetropia hai, near point 1.25 m. Distances metres mein lekar, 1/f=1/0.25−1/1.25, yaani 4−0.8, isliye P=+3.2 D.

    3. R ka defect kya hai, aur iska cause kya hai?

      Solution dikhao

      AnswerPresbyopia, kamzor hoti ciliary muscles aur sakht hote eye lens ki wajah se.

      Umar ke saath R ka near point door khisak gaya hai: presbyopia. Ciliary muscles kamzor ho gayi hain aur lens kam flexible ho gaya hai, isliye woh paas ke objects ke liye utna curved nahi ho paata. Convex reading glasses madad karte hain.

    4. Tumhe kya lagta hai, S ko kis tarah ke spectacles diye jaayenge? Unka description do.

      Solution dikhao

      AnswerBifocals: upar ka part concave, neeche ka part convex.

      S ko door ke liye concave lens aur padhne ke liye convex lens chahiye, isliye S ko bifocal lenses diye jaayenge: door dekhne ke liye upar ka part concave, padhne ke liye neeche ka part convex.

  15. Quick answerEasy

    Har observation ko uske cause se match karo.

    Left mein koi item tap karo, phir right mein uska match.

    Answer dekho
    Answer
    • Taare twinkle karte hain : atmospheric refraction
    • Baarish ke baad rainbow : dispersion aur internal reflection
    • Dhool bhare kamre mein dikhti dhoop ki kiran : Tyndall effect
    • Ugne se pehle dikhta Sun : hawa se light ka mudna
    Twinkling aur advance sunrise atmospheric refraction se hote hain; rainbow internal reflection ke saath dispersion se; dikhti beam particles ki scattering (Tyndall effect) se.
  16. DiagramMedium

    Triangular glass prism se guzarti light ki ray ka labelled diagram banao. Incident ray, refracted ray, emergent ray, angle of incidence, angle of emergence aur angle of deviation mark karo. Emergent ray kis direction mein mudti hai?

    Solution dikhao

    AnswerFig. 10.7 dekho; emergent ray prism ke base ki taraf mudti hai.

    Triangular outline banao. Pehle face se milti incident ray aur wahan ka normal banao; angle i mark karo. Andar normal ki taraf mudi refracted ray banao. Doosre face par normal aur usse door mudi emergent ray banao; angle e mark karo. Incident ray ko aage aur emergent ray ko peeche badhao; unke beech ka angle, angle of deviation D hai. Emergent ray prism ke base ki taraf mudti hai, jaise Fig. 10.7 mein.

Apna NCERT exercise question dhoondo

Hamare practice questions ncert.ai ke liye likhe gaye hain aur NCERT exercises ko follow karte hain. Apni textbook ke question se match karne wala question dhoondo; uska answer uske saath hai.

Tumhari NCERT textbook meinYahan practice question
NCERT in-text Questions p. 164, Q1Practice 10.1 (NCERT ke in-text questions, p. 164) · Q1
NCERT in-text Questions p. 164, Q2Practice 10.1 (NCERT ke in-text questions, p. 164) · Q2
NCERT in-text Questions p. 164, Q3Practice 10.1 (NCERT ke in-text questions, p. 164) · Q3
NCERT in-text Questions p. 164, Q4Practice 10.1 (NCERT ke in-text questions, p. 164) · Q4
NCERT Exercises Q1Exercises · Q1
NCERT Exercises Q2Exercises · Q2
NCERT Exercises Q3Exercises · Q3
NCERT Exercises Q4Exercises · Q4
NCERT Exercises Q5Exercises · Q5
NCERT Exercises Q6Exercises · Q6
NCERT Exercises Q7Exercises · Q7
NCERT Exercises Q8Exercises · Q8
NCERT Exercises Q9Exercises · Q9
NCERT Exercises Q10Exercises · Q10
NCERT Exercises Q11Exercises · Q11
NCERT Exercises Q12Exercises · Q12

Quick check: MCQs

  1. 10.1 Human Eye3 questions
  2. 10.1.1 Power of Accommodation4 questions
  3. Presbyopia4 questions
  4. 10.3 Prism se Light ka Refraction3 questions
  5. Rainbow4 questions
  6. Advance sunrise aur delayed sunset4 questions
  7. 10.6.2 Saaf Aasmaan ka Colour Blue Kyun Hota Hai?4 questions
Glossary · 15

Key terms (English + Hindi)

angle of deviationविचलन कोणvichalan kon
Prism se guzarti light ke liye incident ray aur emergent ray ke beech ka angle.Chapter mein pehli baar yahan aaya →
atmospheric refractionवायुमंडलीय अपवर्तनvayumandaliya apavartan
Earth ke chaaron taraf ki hawa se light ka mudna, jiska refractive index oonchai ke saath aur pal-pal badalta hai.Chapter mein pehli baar yahan aaya →
ciliary musclesपक्ष्माभी पेशियाँpakshmabhi peshiyan
Eye lens ke chaaron taraf ki muscles jo uski curvature aur isliye focal length badalti hain.Chapter mein pehli baar yahan aaya →
corneaस्वच्छ मंडलswachchh mandal
Aankh ki saaf, curved front surface jisse light andar aati hai; light ki zyadatar bending yahi karti hai.Chapter mein pehli baar yahan aaya →
dispersionविक्षेपणvikshepan
White light ka uske colours mein alag hona, kyunki har colour alag angle se mudta hai.Chapter mein pehli baar yahan aaya →
far pointदूर बिंदुdoor bindu
Sabse door ka point jise aankh saaf dekh sakti hai; normal eye ke liye infinity par.Chapter mein pehli baar yahan aaya →
hypermetropiaदीर्घ-दृष्टि दोषdeergh-drishti dosh
Paas ke objects blur hote hain kyunki unki image retina ke peeche banti; convex lens se correct hota hai.Chapter mein pehli baar yahan aaya →
myopiaनिकट-दृष्टि दोषnikat-drishti dosh
Door ke objects blur hote hain kyunki unki image retina ke aage banti hai; concave lens se correct hota hai.Chapter mein pehli baar yahan aaya →
near pointनिकट बिंदुnikat bindu
Sabse paas ka point jahan aankh bina strain ke saaf dekhti hai; normal young eye ke liye lagbhag 25 cm.Chapter mein pehli baar yahan aaya →
power of accommodationसमंजन क्षमताsamanjan kshamata
Eye lens apni focal length kaise badalta hai taaki paas aur door dono objects focus mein aayein.
presbyopiaजरा-दूरदृष्टिताjara-doordrishtita
Umar ke saath accommodation ka kam hona, jisse near point door khisakta hai; convex ya bifocal lenses se correct hota hai.Chapter mein pehli baar yahan aaya →
retinaदृष्टिपटलdrishtipatal
Aankh ke peeche ki light-sensitive layer jis par image banti hai.Chapter mein pehli baar yahan aaya →
scattering of lightप्रकीर्णनprakeernan
Chhote particles se takrane par light ka kai directions mein bhej diya jaana.Chapter mein pehli baar yahan aaya →
spectrumस्पेक्ट्रमspectrum
White light ko disperse karne par milne wali rangon ki patti (VIBGYOR).Chapter mein pehli baar yahan aaya →
Tyndall effectटिंडल प्रभावTyndall prabhav
Chhote particles dwara light ki scattering jisse beam ka raasta dikh jaata hai.Chapter mein pehli baar yahan aaya →

Tum chapter ke end tak pahunch gaye