Class 7 Science Chapter 11: Light: Shadows and Reflections (Hinglish Notes)

Ye chapter kis baare mein hai?

Western Ghats mein chhuttiyon ke dauraan Keshav andhere mein saikdon jugnuon ko chamakte dekhta hai. Use pata chalta hai ki ye keede roshni se ek doosre se baat karte hain, aur light pollution, ghatte jungle aur bahut zyaada sailaaniyon ki wajah se kam hote ja rahe hain. Ghar lautte hue bus se wo chaandni mein nahaayi pahaadiyan dekhta hai aur sochta hai: kya Moon apni roshni banata hai? Aur headlight ki roshni seedhi lakeer jaisi kyun dikhti hai? Ye chapter aise sawaalon ke jawab deta hai: roshni kahan se aati hai, kaise chalti hai, aur cheezon aur mirror se milne pe kya hota hai.

Roshni ke srot

Sun hamari kudrati roshni ka mukhya srot hai: wo apni roshni emit karta, yaani deta hai. Taare, aasmaani bijli, kudrati aag aur jugnu jaise kuch jaanwar bhi roshni dete hain. Insaan ne pehle aag se roshni banaayi, phir tel, mom ya gas jalaane waale deepakon se, aur aaj zyaadatar bijli ke lamp se. Jo cheezein apni roshni deti hain wo luminous hain; jo nahi deti wo non-luminous. Moon non-luminous hai: chaandni asal mein Moon se reflect hui dhoop hai. Naye LED lamp bahut kam bijli lete hain, zyaada roshni dete hain aur zyaada din chalte hain, par kharab hone pe unhe recycle karna chahiye, kachre mein nahi phenkna chahiye.

Roshni seedhi line mein chalti hai

Ek line mein khade teen maachis ke dabbon ke chhedon se torch chamkaao, to screen pe chamakdaar spot banta hai; ek dabba thoda khiskaao aur spot gaayab. Moambatti ki lau seedhi pipe ke us paar dikhti hai par mudi pipe se kabhi nahi. Ek boond doodh waale paani mein laser ki roshni bhi seedhi chalti dikhti hai. Ye sab dikhaate hain ki roshni seedhi line mein chalti hai.

Transparent, translucent aur opaque

Saaf kaanch jaisi transparent cheezon se lagbhag saari roshni guzarti hai, tracing paper jaisi translucent cheezon se thodi, aur cardboard jaisi opaque cheezon se bilkul nahi. Aur padho parchhaai kaise banti hai? mein.

Parchhaai

Jab koi opaque cheez roshni ke raaste mein aati hai, to wo roshni rok leti hai, aur uske peechhe ki satah pe ek andhera hissa, yaani parchhaai, banta hai. Parchhaai dekhne ke liye roshni ka srot, opaque cheez aur screen, jaise deewar ya zameen, chahiye. Cheez, roshni aur screen ki jagah badalne se parchhaai ka aakaar, size aur tez kinaare badalte hain, par cheez ka rang badalne se parchhaai ka rang nahi badalta. Translucent cheezein halki parchhaai banati hain. India ki kai parchhaai kathputli kalaayein, jaise Andhra Pradesh ki Tholu Bommalata aur Odisha ki Ravana Chhaya, isi pe tiki hain.

Reflection aur plane mirror

Chamakdaar thaali ya mirror dhoop ka ek chamakdaar dhabba chhaaon waali deewar pe phenk sakta hai: wo roshni ki disha badal deta hai. Ise reflection of light kehte hain. Sapaat, yaani plane, mirror aisa image banata hai jo object ke same size ka, erect (seedha), mirror ke peechhe utna hi door jitna object aage hai, aur screen pe nahi aata. Ye laterally inverted bhi hota hai: left aur right badal jaate hain, isiliye ambulance pe AMBULANCE ulta likha hota hai. Dekho reflection aur plane mirror.

Pinhole camera, periscope aur kaleidoscope

Pinhole camera mein kisi cheez ki roshni ek chhote chhed se guzarkar screen pe image banati hai. Image ulta (inverted) hota hai, kyunki cheez ke upar aur neeche ki roshni chhed pe ek doosre ko kaatti hai. Padho pinhole camera kaise banayein?. Mirror kaam ke khilone aur aujaar bhi banaate hain: periscope do plane mirror se deewar ke paar dikhaata hai, aur kaleidoscope teen mirror se anginat design banata hai. Har jawab Chapter 11 ke NCERT solutions mein hai.