Class 8 Science · Chapter 10
Short answer:
Class 8 Science Chapter 10 — Light: Mirrors and Lenses: is chapter me light ka rectilinear propagation, reflection ke laws, plane/concave/convex mirrors, convex/concave lenses, aur real vs virtual image ke concepts cover hote hain — poori tarah ray diagram aur mirror/lens formula based numericals ke saath.
Chapter 10 poore Class 8 Science 'Curiosity' textbook ka sabse visual aur experiment-friendly chapter hai — jab bhi hum aaine me apna chehra dekhte hain ya paani me doobi hui stick ko tedhi dekhte hain, tab yehi Light: Mirrors and Lenses ka concept kaam kar raha hota hai. Ye chapter light ke rectilinear propagation, reflection ke laws, plane aur spherical mirrors (concave-convex), lenses (convex-concave), aur real vs virtual image jaise foundational concepts cover karta hai — jo aage Class 10 ki detailed Physics ki neev banate hain.
Naye rationalised NCERT syllabus (2026-27 session) me purane optional-heavy chapters jaise Sound, Friction, aur Chemical Effects of Electric Current ko hata kar textbook ko streamline kiya gaya hai — is trend ko dekh sakte ho neighbouring chapters me bhi, jaise class 8 science exploring forces notes, pressure winds storms and cyclones class 8 explanation, aur electricity magnetic and heating effects class 8 numericals — ye sab ab ek connected, application-focused Curiosity book ka hissa hain, na ki alag-alag disconnected topics.
Chapter 10 Summary — 5 Minute Revision
Chapter 10 "Light: Mirrors and Lenses" Class 8 Science ke Curiosity textbook ka core optics chapter hai jo light ke basic properties — rectilinear propagation, reflection, aur refraction — ko real-life examples ke saath samjhata hai. Plane mirror hamesha virtual, erect, aur laterally-inverted image banata hai; concave mirror (converging) object ki position ke hisaab se real ya virtual image bana sakta hai, jabki convex mirror (diverging) hamesha virtual aur diminished image deta hai. Isi tarah convex lens converging aur concave lens diverging behave karte hain.
Mirror formula (1/v + 1/u = 1/f) aur magnification (m = −v/u) numericals solve karne ke liye critical hain — CBSE marking scheme me step-by-step working, correct sign convention, aur final answer ki units zaroor likhni chahiye. Ye concepts aage Class 10 Physics ke detailed "Light — Reflection and Refraction" chapter ki neev banate hain, isliye ray diagrams practice karna is stage par bahut zaroori hai.
In-Text Questions — Solutions
Activity-based question: Ek plane mirror ke saamne khadi ho kar apna image dekho — kya image real hai ya virtual? Kyun?
Plane mirror me banne wali image virtual hoti hai kyunki light rays actually mirror ke peeche milti nahi hain — sirf unka backward extension (kalpit rekhayen) ek point par milta hua dikhta hai. Isliye is image ko screen par capture nahi kiya ja sakta, sirf aankh se dekha ja sakta hai. Ye erect (seedhi) aur object ke size ke barabar (magnification = 1) hoti hai, lekin laterally inverted hoti hai — left-right ulti dikhti hai.
Concave mirror me agar object focus (F) par rakha jaaye to image kahan banegi?
Jab object concave mirror ke focus (F) par rakha jaata hai, to reflected rays ek dusre ke parallel ho jaati hain aur kabhi nahi milti. Isliye image infinity par banti hai — highly magnified aur real (theoretically). Ye principle torch aur headlight ke design me use hota hai, jaha bulb ko focus par rakh kar parallel, strong beam banayi jaati hai.
Convex lens se object 2F1 par rakhne par kaisi image banegi?
Jab object convex lens ke 2F1 (focus se double distance) par rakha jaata hai, to image bhi doosri taraf 2F2 par hi banti hai. Ye image real, inverted, aur object ke size ke barabar (same size, magnification = 1) hoti hai. Ye ek important special case hai jo photocopier ke same-size copy banane ke concept me use hota hai.
Exercise Questions — Solutions (Q1–Q6)
1. Define the following terms: (a) Rectilinear propagation of light (b) Reflection of light (c) Real image (d) Virtual image
(a) Rectilinear propagation of light: Light hamesha ek seedhi line me travel karta hai jab tak uska path homogeneous medium me na tootey (obstacle ya medium change na ho). Isi property ki wajah se shadows bante hain aur pinhole camera kaam karta hai.
(b) Reflection of light: Jab light kisi surface (jaise mirror) se takra kar wapas usi medium me laut aati hai, use reflection kehte hain. Ye Laws of Reflection follow karta hai — angle of incidence = angle of reflection.
(c) Real image: Wo image jo light rays ke actual milne (converge hone) se banti hai aur screen par capture ki ja sakti hai. Ye hamesha inverted hoti hai. Example — concave mirror/convex lens se object ko focus se door rakhne par banne wali image.
(d) Virtual image: Wo image jo light rays ke actual milne se nahi, balki unke backward extension (kalpit rekhaon) se banti hai. Ise screen par capture nahi kiya ja sakta, sirf aankh ya mirror me dekha ja sakta hai. Example — plane mirror ki image hamesha virtual hoti hai.
2. A ray of light is incident on a plane mirror at an angle of 40° to the mirror surface. Find the angle of reflection.
Angle of incidence, mirror surface se diya gaya hai = 40°
Lekin angle of incidence (i) hamesha normal se measure hota hai, surface se nahi.
Normal se angle of incidence = 90° − 40° = 50°
Law of Reflection ke according, angle of incidence = angle of reflection.
Angle of reflection (normal se) = 50°
Mirror surface se angle of reflection = 90° − 50° = 40°.
3. State the differences between a concave mirror and a convex mirror. Give one use of each.
| Concave Mirror | Convex Mirror |
|---|---|
| Reflecting surface curved inward (bowl jaisa) | Reflecting surface curved outward (bulge) |
| Converging mirror — parallel rays ek point (focus) par milti hain | Diverging mirror — parallel rays bikhar jaati hain, unka backward extension focus par milta hai |
| Real ya virtual, chhoti-badi dono tarah ki image bana sakta hai (object ki position par depend karta hai) | Hamesha virtual, erect aur diminished image banata hai |
| Use: Shaving/makeup mirror, torch/headlight reflector, dentist ka mirror | Use: Vehicle ka side/rear-view mirror (kyunki wide field of view deta hai) |
↔ Table ko side me swipe karein
4. What is the difference between a convex lens and a concave lens? Draw ray diagrams to show image formation by a convex lens when the object is placed beyond 2F.
Convex lens beech me mota aur edges par patla hota hai — ye converging lens hai, parallel rays ko ek focus point par milata hai. Concave lens beech me patla aur edges par mota hota hai — ye diverging lens hai, parallel rays ko bikher deta hai.
Ray diagram (object beyond 2F, convex lens):
Jab object 2F1 se pare rakha jaata hai:
- Ek ray object ke top se principal axis ke parallel jaati hai, lens se refract hokar focus F2 se guzarti hai.
- Doosri ray optical centre se seedhi guzarti hai, bina deviate hue.
- Dono rays F2 aur 2F2 ke beech me milti hain.
Image ki nature: Real, inverted, aur diminished (chhoti), F2 aur 2F2 ke beech banti hai.
5. Explain why a straight stick appears bent when partially immersed in water.
Ye phenomenon refraction of light ki wajah se hota hai.
Jab light ray paani (denser medium) se hawa (rarer medium) me jaati hai, to wo apna path change kar leti hai — normal se door bend hoti hai (jab rarer medium me jaa rahi ho). Stick ke jo hisse paani ke andar hain, unse aane wali light rays refract hoti hain, jabki upar wale hisse ki rays refract nahi hoti (hawa se seedhe aankh tak).
Hamari aankh yeh maan leti hai ki light hamesha seedhi line me travel karti hai, isliye brain in refracted rays ko unke actual path ki jagah ek seedhi line me extend kar deta hai. Isse stick ka underwater hissa apni actual position se hata hua (bent) dikhta hai.
6. An object is placed at a distance of 20 cm from a concave mirror of focal length 15 cm. Using the mirror formula, find the position of the image.
Concave mirror ke liye sign convention (object real side positive, incident direction lena) use karte hue, standard NCERT convention me:
Object distance, u = −20 cm, Focal length, f = −15 cm (concave mirror)
Mirror formula:
1/v + 1/u = 1/f
1/v = 1/f − 1/u = 1/(−15) − 1/(−20)
1/v = −1/15 + 1/20 = (−4 + 3)/60 = −1/60
v = −60 cm
Negative sign batata hai ki image mirror ke saamne (real side) par banti hai, i.e. image real hai aur mirror se 60 cm door banti hai.
Important Equations — Ek Nazar Me
| Concept | Formula / Rule |
|---|---|
| Law of Reflection | Angle of incidence (i) = Angle of reflection (r), dono normal se measure hote hain |
| Mirror Formula | 1/v + 1/u = 1/f |
| Lens Formula | 1/v − 1/u = 1/f |
| Magnification (mirror/lens) | m = h′/h = −v/u |
| Focal length aur Radius of curvature | f = R/2 (spherical mirrors ke liye) |
| Rectilinear propagation | Light homogeneous medium me straight line me travel karti hai |
↔ Table ko side me swipe karein
Common Mistakes — Yahan Marks Kat te Hain
- Angle of incidence/reflection ko mirror surface se measure kar lete hain — yaad rakho, ye hamesha NORMAL (perpendicular line) se measure hota hai, surface se nahi.
- Real aur virtual image ko confuse kar dete hain — real image screen par capture ho sakti hai (rays actually milti hain), virtual image nahi (sirf extension milta hai).
- Concave aur convex mirror/lens ke naming me galti — concave mirror converging hota hai jabki concave LENS diverging hota hai. Dono opposite behave karte hain.
- Mirror formula aur lens formula ke sign convention ko mix kar dete hain — dono me u, v, f ke signs alag rules follow karte hain, numerical solve karte time convention clearly likho.
- Magnification ka formula galat use karna — m = h'/h ke saath v/u ka sign bhool jaate hain, jisse image ki nature (erect/inverted) galat nikalti hai.
- Refraction ko reflection samajh lena — stick ka paani me tedha dikhna REFRACTION hai (light ka medium change karna), na ki reflection (light ka bounce karna).
Board-Style Important Questions
- Define the laws of reflection of light with a labelled diagram.
- Distinguish between real and virtual images with suitable examples.
- A concave mirror produces a real image 3 times the size of the object placed at 10 cm from it. Find the focal length of the mirror.
- Why does a convex mirror always produce a virtual, erect, and diminished image? Explain with a ray diagram.
- State the rectilinear propagation of light and explain the formation of shadows using this property.
- Explain, with the help of a diagram, why a pencil partly immersed in water appears bent at the surface.
Aksar Poochhe Jaane Wale Sawaal
Class 8 Science Curiosity book me Light: Mirrors and Lenses chapter number kaunsa hai?
Naye rationalised NCERT Class 8 Science 'Curiosity' textbook (2026-27 session) ke 13-chapter structure me ye Chapter 10 hai. Chapter 1 se related — jo Curiosity chapter 1 solutions dhoondh rahe hain unke liye ye alag chapter hai, foundational Matter chapter chapter 1 hai.
Kya is chapter me Sound aur Friction bhi cover hote hain?
Nahi. Rationalisation ke baad Sound aur Friction dono standalone chapters ke roop me hata diye gaye hain — ye purani NCERT me the. Naye Curiosity textbook me sirf Light: Mirrors and Lenses hi optics-related chapter hai.
Concave aur convex mirror me real-life use ka farak kya hai?
Concave mirror converging hota hai isliye shaving/makeup mirrors aur torch reflectors me use hota hai jaha magnified image chahiye. Convex mirror diverging hota hai aur wide field of view deta hai isliye vehicle ke side mirrors me use hota hai.
Mirror formula aur lens formula same hai kya?
Formula ka form same hai — 1/v + 1/u = 1/f — lekin sign convention thoda different apply hota hai mirrors aur lenses ke liye. Dono me v (image distance), u (object distance), f (focal length) hote hain.
Is chapter ke numericals ke liye kaunse formulas yaad rakhne chahiye?
Mirror/lens formula (1/v + 1/u = 1/f), magnification (m = h'/h = −v/u), aur laws of reflection (angle of incidence = angle of reflection) — ye teen sabse zyada numerical-relevant hain.
Class 8 ke baad ye topic kis class me detail me aata hai?
Light — Reflection and Refraction ka detailed treatment Class 10 Physics me hota hai jisme ray diagrams, formulas, aur numericals aur bhi depth me cover hote hain. Class 8 ka ye chapter uski neev banata hai.
Class 8 Science — Saare Chapters
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