Class 10 Science · Chapter 10
Short answer:
Is chapter ke complete NCERT solutions yahan hain — 4 in-text questions (page-end set) aur 13 exercise questions, sab NCERT ke original order me. Coverage: human eye ki structure aur power of accommodation, near point aur far point, teeno common defects (myopia, hypermetropia, presbyopia) unke correction ke saath, lens power ke 4 numericals (−5.5 D / +1.5 D focal length, far point 80 cm, near point 1 m, aur 1.2 m far point wala in-text numerical), glass prism se refraction aur dispersion, recombination of spectrum, rainbow, atmospheric refraction (twinkling of stars, advanced sunrise aur delayed sunset), aur scattering of light (Tyndall effect, blue sky, red Sun, astronaut ko kaala aasman). Saath me defects-of-vision reference table, 6 common exam mistakes, board-style practice questions aur 6 FAQs.
Human eye ek natural camera hai jiska lens apni curvature badal kar focal length change karta hai — aur jab yahi adjustment fail ho jata hai, tab spectacles ki zarurat padti hai.
Ye chapter do hisso me chalta hai. Pehla hissa aankh ka hai: eye lens kaise ciliary muscles ki madad se focal length badalta hai (power of accommodation), aur jab ye system fail hota hai to myopia, hypermetropia ya presbyopia ban jata hai — jinka correction concave ya convex lens se hota hai. Doosra hissa “colourful world” ka hai: prism se white light ka dispersion, rainbow, atmosphere ki wajah se hone wala refraction (stars ka twinkle karna, Sun ka actual sunrise se ~2 minute pehle dikhna) aur scattering of light (aasman neela kyun, doobta hua Sun laal kyun).
Numerical side pe pura chapter ek hi formula pe khada hai — lens formula se focal length nikaalo aur P = 1/f (f metre me) se power. Sign convention hi asli marks decide karta hai: concave lens ka power hamesha minus, convex lens ka hamesha plus.
Chapter 10 Summary — 5 Minute Revision
1. Human Eye — structure aur kaam
- Cornea — aankh ke aage ka transparent bulge. Light jab air se cornea me ghusti hai to sabse zyada refraction yahin hota hai (maximum bending).
- Iris — rangeen part; pupil ka size control karta hai, yaani kitni light andar aayegi. Tez roshni me pupil chhota, andhere me bada.
- Pupil — iris ke beech ka kaala chhed jisse light andar jaati hai.
- Eye lens — fibrous, jelly-like convex lens. Ye image ko sharp focus karta hai aur fine adjustment deta hai (poora bending nahi, wo cornea karta hai).
- Ciliary muscles — lens ki curvature badal kar focal length badalte hain.
- Retina — light-sensitive screen jahan real aur inverted image banti hai. Isme rods (dim light) aur cones (colour) hote hain.
- Optic nerve — signal ko brain tak le jaati hai; brain image ko seedha (erect) samajhta hai.
2. Power of accommodation
- Eye lens ki focal length ko adjust karne ki ability = power of accommodation.
- Door ki cheez dekhte waqt: ciliary muscles relaxed → lens patla (thin) → focal length badi.
- Paas ki cheez dekhte waqt: ciliary muscles contract → lens mota (thick) → focal length chhoti.
- Lens apni jagah nahi badalta (camera ki tarah aage-peeche nahi khiskta) — sirf curvature badalta hai. Image distance (lens se retina) fix rehta hai.
- Focal length ek limit se zyada kam nahi ho sakti, isliye 25 cm se paas ki cheez normal aankh clearly nahi dekh sakti.
3. Near point aur far point
- Near point (least distance of distinct vision) = wo minimum distance jahan tak aankh bina strain ke clearly dekh sakti hai. Normal young adult ke liye 25 cm.
- Far point = maximum distance jahan tak clearly dikhta hai. Normal aankh ke liye infinity.
- Range of vision = 25 cm se infinity tak.
4. Defects of vision aur unka correction
- Myopia (near-sightedness) — paas ki cheez dikhti hai, door ki dhundhli. Far point infinity se kam ho jata hai. Image retina se pehle banti hai. Cause: eye lens ki curvature zyada (focal length chhoti) ya eyeball lamba ho jana. Correction: concave (diverging) lens jiska focal length = person ka far point (minus sign ke saath). Power negative.
- Hypermetropia (far-sightedness) — door ki cheez dikhti hai, paas ki dhundhli. Near point 25 cm se door chala jata hai. Image retina ke peeche banti hai. Cause: focal length zyada lambi ya eyeball chhota. Correction: convex (converging) lens, power positive.
- Presbyopia — umar ke saath ciliary muscles kamzor + lens ki flexibility kam → accommodation power ghat jaati hai. Near point door khisak jata hai. Kabhi-kabhi myopia aur hypermetropia dono ek saath hote hain — tab bi-focal lens lagta hai: upper part concave (door ke liye), lower part convex (padhne ke liye).
- Aajkal in defects ko contact lenses ya surgical (laser) methods se bhi theek kiya jata hai.
5. Refraction through a glass prism
- Prism ke do refracting surfaces ke beech ka angle = angle of prism (A).
- Ray do baar mudti hai — pehle prism me ghuste waqt normal ki taraf, phir nikalte waqt normal se door.
- Incident ray aur emergent ray ke beech ka angle = angle of deviation (D).
- Glass slab me emergent ray incident ray ke parallel hoti hai, prism me nahi — kyunki prism ke do surfaces parallel nahi hote. Yahi dispersion ki wajah banta hai.
6. Dispersion of white light
- White light ka apne saat component colours me split hona = dispersion.
- Spectrum ka order: VIBGYOR — Violet, Indigo, Blue, Green, Yellow, Orange, Red.
- Kaaran: alag-alag colours ke liye glass ka refractive index alag hota hai, isliye har colour alag angle se mudta hai.
- Red sabse kam mudti hai, violet sabse zyada. (Red ki wavelength sabse badi, violet ki sabse chhoti.)
- Newton ka experiment: ek prism se spectrum banaya, phir doosra prism ulta rakh kar sab colours wapas mila diye → white light. Isse siddh hua ki sunlight saat rangon se milkar bani hai.
- Rainbow = baarish ke baad hawa me latke paani ke chhote droplets me hone wala natural spectrum. Droplet me hota hai: refraction → internal reflection → phir refraction. Rainbow hamesha Sun ke opposite direction me dikhta hai.
7. Atmospheric refraction
- Atmosphere ki alag-alag layers ka temperature aur density alag hai, isliye refractive index bhi alag — aur ye lagataar badalta rehta hai.
- Twinkling of stars: star ek point source hai. Uski light atmosphere se guzarte waqt continuously refract hoti hai, isliye apparent position aur apparent brightness thodi-thodi badalti rehti hai — kabhi tez, kabhi mand → twinkle.
- Planets twinkle nahi karte: planet zameen ke bahut paas hai, isliye wo ek extended source hai = bahut saare point sources ka collection. Sabke flickering ka average zero ho jata hai, net brightness constant rehti hai.
- Advanced sunrise aur delayed sunset: atmospheric refraction ki wajah se Sun hume actual sunrise se lagbhag 2 minute pehle dikh jata hai, aur sunset ke ~2 minute baad tak dikhta rehta hai — yaani din lagbhag 4 minute lamba lagta hai. Horizon pe Sun ka disc chapta (flattened) bhi dikhta hai.
8. Scattering of light
- Bahut chhote particles se light ka har direction me phailna = scattering.
- Tyndall effect — colloid ya suspension se guzarti light ka path visible ho jana. Examples: ghane jungle me pedon ke beech se aati sunlight ki beam, dhuen bhare kamre me chhoti chhed se aati light.
- Scattering ka amount particle ke size pe depend karta hai: bahut chhote particles zyadatar choti wavelength (blue) scatter karte hain, bade particles sab wavelengths scatter karte hain (isliye colour white lagta hai — jaise badal).
- Sky blue kyun: hawa ke molecules chhote hote hain — wo blue (short wavelength) ko red se kahin zyada scatter karte hain, aur yahi scattered blue light hume har taraf se aati hai.
- Astronaut ko sky kaala: upar atmosphere nahi hai → scattering nahi → aasman kaala.
- Sunrise/sunset pe Sun laal: us waqt sunlight ko atmosphere ki sabse lambi layer paar karni padti hai. Blue aur short wavelengths raaste me hi scatter ho jaati hain, sirf lambi wavelength wali red hum tak pahunchti hai. Dopahar me Sun sar ke upar hota hai, path chhota, kam scattering → Sun white dikhta hai.
- Danger signals red kyun: red ki wavelength sabse lambi → sabse kam scatter hoti hai → kohre/dhundh me bhi door se dikhti hai.
9. Quick recap table
| Phenomenon | Kaaran |
|---|---|
| Sky blue | Scattering (chhote molecules blue zyada scatter karte hain) |
| Sun red at sunrise/sunset | Scattering (lamba path, blue nikal jaata hai) |
| Stars twinkle | Atmospheric refraction (point source) |
| Advanced sunrise / delayed sunset | Atmospheric refraction |
| Rainbow | Dispersion + internal reflection in water droplets |
| Beam of light visible in mist | Tyndall effect (scattering) |
↔ Table ko side me swipe karein
In-Text Questions — Solutions
Q1. What is meant by power of accommodation of the eye?
Power of accommodation = eye lens ki wo ability jiske through wo apni focal length adjust kar leta hai, taaki paas aur door — dono ki cheezein retina pe sharp focus ho jayein.
Ye kaam ciliary muscles karte hain:
- Door ki object dekhte waqt ciliary muscles relax hote hain → lens patla → focal length badh jaati hai.
- Paas ki object dekhte waqt ciliary muscles contract karte hain → lens mota → focal length ghat jaati hai.
Yaad rakho — lens apni curvature badalta hai, apni position nahi. Lens se retina ka distance fix hai.
Q2. A person with a myopic eye cannot see objects beyond 1.2 m distinctly. What should be the type of the corrective lens used to restore proper vision?
Person myopic hai — uska far point 1.2 m hai, infinity nahi. Correction ke liye concave (diverging) lens chahiye, jo infinity pe rakhi object ka image person ke far point (1.2 m) pe bana de. Tab uski aankh us image ko aaram se dekh legi.
Given: object at infinity, u = −∞; image far point pe, v = −1.2 m
Aise case me lens ki focal length = far point (minus sign ke saath):
f = −1.2 m
P = 1/f = 1/(−1.2) = −0.83 D
Answer: Concave lens, focal length 1.2 m, power −0.83 D (approx). Negative sign confirm karta hai ki lens concave hai.
Q3. What is the far point and near point of the human eye with normal vision?
Normal vision wali aankh ke liye:
- Near point (least distance of distinct vision) = 25 cm — isse paas ki cheez bina strain ke clearly nahi dikhti.
- Far point = infinity — kitni bhi door ki cheez clearly dikh sakti hai.
Yaani normal aankh ki range of vision 25 cm se infinity tak hai.
Q4. A student has difficulty reading the blackboard while sitting in the last row. What could be the defect the child is suffering from? How can it be corrected?
Bachche ko door ki cheez (blackboard) dhundhli dikh rahi hai, paas ki cheez (notebook) theek dikhti hai — ye myopia (near-sightedness / short-sightedness) hai.
Kaaran: ya to eye lens ki curvature zyada ho gayi hai (focal length bahut chhoti), ya eyeball lamba ho gaya hai. Dono case me door ki object ka image retina se pehle ban jata hai.
Correction: suitable power ka concave (diverging) lens pehnana. Ye rays ko retina pe pahunchne se pehle thoda diverge kar deta hai, jisse image peeche khisak kar theek retina pe ban jata hai.
Poore Class 10 Science ke handwritten colour notes
IITian & district toppers ke banaye short notes — revision-ready, diagram ke saath. Board se pehle poora syllabus 3 din me revise.
Exercise Questions — Solutions (Q1–Q13)
Q1. The human eye can focus on objects at different distances by adjusting the focal length of the eye lens. This is due to (a) presbyopia (b) accommodation (c) near-sightedness (d) far-sightedness
Answer: (b) accommodation
Ciliary muscles lens ki curvature badal kar focal length adjust karte hain — isi ability ko power of accommodation kehte hain. Baaki teeno options defects hain, ability nahi.
Q2. The human eye forms the image of an object at its (a) cornea (b) iris (c) pupil (d) retina
Answer: (d) retina
Retina light-sensitive screen hai jahan real aur inverted image banti hai. Cornea refraction karta hai, iris pupil ka size control karta hai, pupil sirf ek opening hai — image koi nahi banata.
Q3. The least distance of distinct vision for a young adult with normal vision is about (a) 25 m (b) 2.5 cm (c) 25 cm (d) 2.5 m
Answer: (c) 25 cm
Yahi near point hai. Unit dhyan se padho — 25 cm, 25 m nahi.
Q4. The change in focal length of an eye lens is caused by the action of the (a) pupil (b) retina (c) ciliary muscles (d) iris
Answer: (c) ciliary muscles
Ciliary muscles contract ya relax hokar lens ki curvature (motai) badalte hain, jisse focal length badalti hai.
Q5. A person needs a lens of power −5.5 dioptres for correcting his distant vision. For correcting his near vision he needs a lens of power +1.5 dioptre. What is the focal length of the lens required for correcting (i) distant vision, and (ii) near vision?
(i) Distant vision
Given: P = −5.5 D
P = 1/f ⇒ f = 1/P
f = 1/(−5.5) = −0.1818 m
f = −0.18 m = −18.2 cm (approx). Negative focal length ⇒ concave lens — sahi hai, kyunki distant vision ka defect myopia hota hai.
(ii) Near vision
Given: P = +1.5 D
f = 1/P = 1/(+1.5) = +0.667 m
f = +0.67 m = +66.7 cm (approx). Positive focal length ⇒ convex lens — near vision ka defect hypermetropia/presbyopia hota hai.
Note: Is vyakti ko dono defect hain, isliye practically bi-focal lens use hoga.
Q6. The far point of a myopic person is 80 cm in front of the eye. What is the nature and power of the lens required to correct the problem?
Nature: myopia ko theek karne ke liye concave (diverging) lens chahiye.
Given:
- Object at infinity ⇒ u = −∞
- Image far point pe banni chahiye ⇒ v = −80 cm = −0.8 m
Lens formula:
1/v − 1/u = 1/f
1/(−0.8) − 1/(−∞) = 1/f
−1.25 − 0 = 1/f ⇒ f = −0.8 m
Power:
P = 1/f = 1/(−0.8) = −1.25 D
Answer: Concave lens, focal length −0.8 m (−80 cm), power −1.25 D.
Q7. Make a diagram to show how hypermetropia is corrected. The near point of a hypermetropic eye is 1 m. What is the power of the lens required to correct this defect? Assume that the near point of the normal eye is 25 cm.
Diagram (describe karke banao): teen parts banao — (a) hypermetropic eye: 25 cm pe rakhi object ki rays retina ke peeche converge hoti dikhao; (b) defect ka reason; (c) corrected eye: aankh ke aage ek convex lens lagao jo 25 cm wali object ka virtual image 1 m pe (aankh ki hi side me) banata hai, aur ab aankh us image ko retina pe focus kar leti hai.
Given:
- Object normal near point pe ⇒ u = −25 cm = −0.25 m
- Image defective eye ke near point pe (virtual, same side) ⇒ v = −100 cm = −1 m
Lens formula:
1/v − 1/u = 1/f
1/(−1) − 1/(−0.25) = 1/f
−1 + 4 = 1/f ⇒ 1/f = 3
f = 1/3 m = +0.33 m = +33.3 cm
Power:
P = 1/f = 1/(1/3) = +3.0 D
Answer: Convex lens of power +3.0 D (focal length +0.33 m).
Q8. Why is a normal eye not able to see clearly the objects placed closer than 25 cm?
Object jitni paas aati hai, uska image retina pe focus karne ke liye eye lens ki focal length utni hi chhoti karni padti hai — yaani ciliary muscles ko aur zyada contract karke lens ko aur mota banana padta hai.
Lekin ciliary muscles ki contraction ki ek limit hai. 25 cm ke baad lens ki focal length aur kam nahi ho paati, isliye image retina pe nahi banti — wo retina ke peeche banne lagti hai aur object blurred dikhta hai. Zabardasti dekhne ki koshish me aankh me strain hota hai.
Isi 25 cm ko near point ya least distance of distinct vision kehte hain.
Q9. What happens to the image distance in the eye when we increase the distance of an object from the eye?
Aankh me image distance nahi badalta — wo constant rehta hai, kyunki eye lens aur retina ke beech ka distance fix hai. Image hamesha retina pe hi banni chahiye.
Jo cheez badalti hai wo hai focal length: object door jaate hi ciliary muscles relax ho jaate hain, lens patla ho jata hai aur focal length badh jaati hai — taaki image phir bhi theek retina pe hi bane.
(Agar sawal ko simple lens ki tarah socho to image ka size chhota ho jata hai, par eye me v constant hi rehta hai.)
Q10. Why do stars twinkle?
Star bahut door hai, isliye wo hume ek point source of light lagta hai.
Star ki light jab Earth ke atmosphere se guzarti hai to har layer ka refractive index alag hone ki wajah se wo lagataar refract hoti rehti hai, aur atmosphere ki condition (temperature, density) bhi lagataar badalti rehti hai. Isliye star ki apparent position thodi-thodi shift hoti rehti hai.
Jab hum tak pahunchne wali light ki amount badalti hai, star kabhi thoda bright lagta hai kabhi thoda dim — yahi twinkling hai.
Q11. Explain why the planets do not twinkle.
Planets Earth ke bahut zyada paas hain, isliye wo point source nahi balki extended source ki tarah behave karte hain — yaani bahut saare point sources ka collection.
Har point source apne aap flicker karta hai, lekin sabke flickering ka average nil ho jata hai — kisi point ki light kam ho rahi hoti hai to kisi ki zyada. Net result: planet se aane wali total light constant rehti hai, isliye planet twinkle nahi karte.
Q12. Why does the Sun appear reddish early in the morning?
Sunrise (aur sunset) ke waqt Sun horizon ke paas hota hai, isliye uski light ko atmosphere ki sabse lambi motai paar karke hum tak aana padta hai.
Itne lambe raaste me chhoti wavelength wali blue light zyadatar scatter hokar nikal jaati hai, aur sirf lambi wavelength wali red light seedhi hum tak pahunchti hai — isliye Sun laal/orange dikhta hai.
Iske ulta, dopahar me Sun sar ke upar hota hai, light ka atmospheric path sabse chhota hota hai, scattering kam hoti hai — isliye Sun white dikhta hai.
Q13. Why does the sky appear dark instead of blue to an astronaut?
Aasman ka neela rang scattering of light ki wajah se hai — hawa ke chhote molecules blue (short wavelength) light ko zyada scatter karte hain, aur wahi bikhri hui blue light har taraf se hum tak aati hai.
Astronaut jab bahut oonchai pe ya space me hota hai, wahan atmosphere hi nahi hota — scattering karne wale molecules nahi hain. Isliye uske paas sirf wahi light pahunchti hai jo seedhi Sun ya stars se aa rahi ho, baaki direction se kuch nahi aata — aur sky kaala dikhta hai.
Important Equations — Ek Nazar Me
Defects of Vision — Reference Table
| Defect | Cause | Image banti kahan hai | Corrective lens | Power ka sign |
|---|---|---|---|---|
| Myopia (near-sightedness) door dhundhla |
Eye lens ki curvature zyada (focal length chhoti) ya eyeball lamba | Retina se pehle (aage) | Concave (diverging) f = far point (with − sign) |
Negative (−) |
| Hypermetropia (far-sightedness) paas dhundhla |
Eye lens ki focal length zyada lambi ya eyeball chhota | Retina ke peeche | Convex (converging) | Positive (+) |
| Presbyopia (old-age vision) |
Ciliary muscles kamzor + eye lens ki flexibility kam → accommodation power ghat gaya | Paas ki object ka image retina ke peeche | Convex; agar myopia bhi ho to bi-focal (upar concave, neeche convex) | Positive (+) reading part ke liye |
↔ Table ko side me swipe karein
Key values — normal eye
| Quantity | Value |
|---|---|
| Near point (least distance of distinct vision) | 25 cm (0.25 m) |
| Far point | Infinity (∞) |
| Range of vision | 25 cm → infinity |
| Near point of a young child (approx) | lagbhag 7–8 cm |
| Advanced sunrise / delayed sunset (atmospheric refraction) | lagbhag 2 minute har taraf |
| Image on retina | Real aur inverted |
↔ Table ko side me swipe karein
Formulas
| Formula | Use / Notes |
|---|---|
| P = 1/f | Power of lens. f zaroor metres me daalo. Unit = dioptre (D). |
| 1/v − 1/u = 1/f | Lens formula. Sign convention: u hamesha negative, virtual image (lens ki same side) ka v negative. |
| Myopia: f = −(far point in m) | Object at infinity, image far point pe. |
| Hypermetropia: u = −0.25 m, v = −(near point in m) | Object normal near point pe, virtual image defective near point pe. |
↔ Table ko side me swipe karein
Common Mistakes — Yahan Marks Kat te Hain
- Myopia aur hypermetropia ke lens ulta likh dena. Sabse common galti. Trick yaad rakho — Myopia = Minus = concave. Myopia me image retina se pehle ban rahi hai, to rays ko thoda diverge karna hai → concave lens. Hypermetropia me image retina ke peeche ban rahi hai, to rays ko aur converge karna hai → convex lens, power positive.
- Lens power ka sign ya unit galat. Do alag galtiyan ek saath hoti hain — (a) concave lens ka power +1.25 D likh dena (hamesha −1.25 D hoga), aur (b) focal length cm me rakh kar P = 1/f kar dena. P = 1/f me f metres me hi chahiye. f = −80 cm ko pehle −0.8 m banao, tab P = −1.25 D. Answer ke saath D (dioptre) likhna mat bhoolo.
- Yeh kehna ki eye lens aage-peeche khisak kar focus karta hai. Wo camera hoti hai. Human eye me lens ki position fix hai — ciliary muscles lens ki curvature (motai) badalte hain, jisse focal length change hoti hai. Image distance (lens se retina) constant rehta hai.
- Dispersion aur scattering ko mix kar dena. Ye alag phenomena hain. Dispersion = white light ka apne colours me split hona kyunki har colour ka refractive index alag hai (prism, rainbow). Scattering = light ka chhote particles se har direction me phailna (blue sky, red Sun, Tyndall effect). “Sky blue hai kyunki dispersion hoti hai” — ye galat hai.
- Twinkling ki wajah scattering bata dena. Stars ka twinkle karna atmospheric refraction ki wajah se hai (badalta hua refractive index → apparent position aur brightness badalti hai), scattering ki wajah se nahi. Isi tarah advanced sunrise bhi refraction hai, scattering nahi.
- Hypermetropia numerical me u aur v ulta rakh dena. Sahi setup: object normal near point pe rakho → u = −25 cm; image defective eye ke near point pe banao, aur wo virtual hai isliye v bhi negative → v = −100 cm. Bahut students v ko +100 cm (+1 m) likh dete hain, jisse 1/f = 1 + 4 = 5 aa jata hai aur answer +5.0 D nikalta hai — jabki sahi answer +3.0 D hai.
Board-Style Important Questions
- 1 mark: Human eye me image kis part pe banti hai, aur uski nature (real/virtual, erect/inverted) kya hoti hai?
- 2 marks: Myopia aur hypermetropia me do antar likho — image kahan banti hai aur correction ke liye kaunsa lens use hota hai.
- 3 marks: Ek myopic person ka far point 50 cm hai. Correction ke liye required lens ki nature, focal length aur power nikaalo. Ray diagram bhi banao (defect aur correction dono).
- 3 marks: Prism se white light ke dispersion ko labelled diagram ke saath samjhao. Batao ki red light sabse kam aur violet sabse zyada kyun mudti hai, aur Newton ne recombination se kya siddh kiya.
- 5 marks: (a) Power of accommodation kya hai aur ciliary muscles ka isme kya role hai? (b) Ek hypermetropic eye ka near point 75 cm hai — 25 cm pe padhne ke liye required lens ka power nikaalo. (c) Sunset ke waqt Sun laal kyun dikhta hai, jabki dopahar me white?
Quick Quiz — Score Check Karein
Q1. Human eye ka wo part jahan light entry karte hi sabse zyada refraction hoti hai — wo kaunsa hai?
Q2. Ciliary muscles kis cheez ko badal kar eye lens ki focal length change karte hain?
Q3. Normal young adult ke liye near point (least distance of distinct vision) kitna hota hai?
Q4. Myopic aankh me object ka image kahan banta hai?
Q5. Ek myopic person ka far point 80 cm hai. Correction ke liye required lens ki power kitni hogi?
Q6. Hypermetropic eye ka near point 1 m hai (normal near point 25 cm maan kar). Correction lens ka power kya hoga?
Q7. White light jab glass prism se guzarti hai, to VIBGYOR order me sabse kam aur sabse zyada kaun si colour mudti hai?
Q8. Stars twinkle karte hain lekin planets nahi — iski asli wajah kya hai?
Q9. Sunset ke waqt Sun laal kyun dikhta hai?
Q10. Astronaut ko space me sky kaala kyun dikhta hai jabki Earth se blue?
Aksar Poochhe Jaane Wale Sawaal
Myopia aur hypermetropia me lens yaad rakhne ka koi easy trick hai?
Haan — 'Myopia = Minus'. Myopia ka corrective lens concave hota hai aur uska power hamesha negative (minus) hota hai. Jo bacha, wo hypermetropia = convex = plus. Ek aur tarika: myopia me image retina se pehle ban rahi hai, to use peeche dhakelna hai, iske liye rays ko diverge karo (concave). Hypermetropia me image peeche ban rahi hai, to use aage laana hai, iske liye converge karo (convex).
P = 1/f me f cm me daal sakte hain kya?
Bilkul nahi. Dioptre ki definition hi ye hai ki f metres me ho. Agar f = 50 cm hai to pehle use 0.5 m banao, phir P = 1/0.5 = +2 D. Agar cm daal doge to answer 100 guna galat aayega — aur ye numerical me sabse zyada marks kaatne wali galti hai.
Presbyopia aur hypermetropia same cheez hai kya?
Nahi. Dono me paas ki cheez dhundhli dikhti hai aur dono me convex lens lagta hai, isliye confusion hoti hai. Par kaaran alag hai: hypermetropia eyeball ke chhote hone ya lens ki focal length lambi hone se hota hai aur kisi bhi umar me ho sakta hai. Presbyopia umar badhne se hota hai — ciliary muscles kamzor ho jaate hain aur lens ki flexibility khatam ho jaati hai, yaani accommodation power hi kam ho jaati hai.
Aasman neela hai to Sun doobte waqt laal kyun ho jata hai — dono me scattering hi to hai?
Scattering dono me hai, bas dekhne ka angle alag hai. Din me hum aasman ki taraf dekhte hain aur hume wo blue light dikhti hai jo scatter hokar side se hum tak aayi. Sunset pe hum seedha Sun ki taraf dekhte hain — aur us seedhi beam me se blue light lambe atmospheric path me scatter hokar nikal chuki hoti hai, sirf red bachi rehti hai. Isliye scattered light blue hai par transmitted (seedhi) light red.
Rainbow me hamesha red upar aur violet neeche kyun hota hai?
Water droplet me light pehle refract hoti hai, phir andar total internal reflection hoti hai, phir bahar nikalte waqt dobara refract hoti hai. Is process me red light droplet se lagbhag 42 degree pe aur violet lagbhag 40 degree pe aankh tak pahunchti hai. Zyada angle wali red light unchey wale droplets se aati hai, isliye primary rainbow me red arc sabse upar aur violet sabse neeche dikhta hai.
Board exam me is chapter se kaunse topics sabse zyada important hain?
Practically har saal repeat hone wale core topics: (1) power of accommodation aur ciliary muscles ka role, (2) teeno defects ka cause + correction + ray diagram, (3) lens power ke numericals (P = 1/f), (4) dispersion aur Newton ka recombination experiment, (5) scattering-based reasoning questions — blue sky, red Sun, astronaut ko kaala aasman, danger signal red — aur (6) atmospheric refraction se twinkling aur advanced sunrise. Diagrams zaroor practice karo, kyunki defects wale questions me diagram alag se maange jaate hain.
Class 10 Science — Saare Chapters
Board exam tak sirf revision karna hai?
Class 10 Science ke saare chapters ke colour handwritten short notes — diagrams, formulas aur important points ek jagah.
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