Class 7 Science · Chapter 7
Short answer:
Heat Transfer in Nature chapter yeh sikhata hai ki heat kis tarah teen tarikon se travel karti hai — conduction (solids, particle-se-particle), convection (liquids/gases, particles khud move karte hain), aur radiation (bina medium ke, jaise Sun se Earth tak). Land breeze, sea breeze, thermos flask, aur kapdon ke colour choice jaise real-life examples is chapter ka core hain.
NCERT Class 7 Science 'Curiosity' book ka Chapter 7 — Heat Transfer in Nature — un chapters mein se hai jo aage Class 8, 9, 10 ki thermal physics ki neev banata hai. Waise hi yeh chapter samjhata hai ki heat kaise ek jagah se doosri jagah move karti hai — chahe woh garam chai ka chammach ho, samundar kinare ki thandi hawa, ya phir Sun ki roshni jo lakhon kilometer dur se bina kisi medium ke humtak pahunchti hai. Yeh 12-chapter "Curiosity" book pehle wali 13-chapter book se kaafi streamlined hai — 2026-27 session ke syllabus rationalisation mein kuch purane chapters jaise Motion and Time ya Electric Current and its Effects ab standalone nahi rahe. Is chapter mein hum dekhenge ki heat transfer ke teen main modes — conduction, convection, aur radiation — hamare aas-paas roz kaise kaam karte hain: cooking se lekar coastal areas ki land-sea breeze tak.
Chapter 7 Summary — 5 Minute Revision
Heat Transfer in Nature chapter humein sikhata hai ki heat hamesha higher temperature se lower temperature ki taraf flow karti hai, jab tak dono objects thermal equilibrium mein nahi aa jaate. Iske teen modes hain — conduction (solids mein particle-se-particle, medium zaroori), convection (liquids/gases mein particles ke actual movement se, medium zaroori), aur radiation (bina kisi medium ke, electromagnetic waves ke through — jaise Sun ki heat).
Metals jaise copper, silver achhe conductors hote hain kyunki unme free electrons hote hain jo fast heat carry karte hain; wood, plastic, air insulators hote hain. Land aur sea breeze convection ka classic real-world example hain — din mein sea breeze (samundar se zameen ki taraf) aur raat mein land breeze (zameen se samundar ki taraf) banti hai, kyunki zameen paani se jaldi garam aur jaldi thandi hoti hai. Thermos flask apni vacuum wall aur silvered coating se teeno modes ko block karke liquid ka temperature maintain rakhta hai. Roz ki life mein hum light-coloured kapde garmi mein pehente hain kyunki wo radiation kam absorb karte hain, jabki dark colours zyada absorb karte hain.
In-Text Questions — Solutions
Chapter ke shuru mein diya gaya thought activity: garam cup ko haath se pakadne par haath garam kyun feel hota hai?
Jab hum garam cup ko pakadte hain, cup ki heat energy conduction ke through hamari skin ke particles tak transfer hoti hai — cup ke molecules zyada vibrate kar rahe hote hain aur wo apni energy hamari skin ke molecules ko de dete hain, jisse hamein garmi feel hoti hai. Yeh heat hamesha higher temperature (cup) se lower temperature (haath) ki taraf flow karti hai.
Ek beaker mein paani ubalte waqt neeche se bubbles kyun uthte dikhte hain?
Jab beaker ko neeche se garam kiya jaata hai, neeche ka paani pehle garam hota hai aur halka (less dense) ho jaata hai, isliye woh upar uthta hai. Upar ka thanda, zyada dense paani neeche aata hai aur garam hota hai. Yeh cycle repeat hota rehta hai jisse convection current banti hai — yehi cycle boiling ke bubbles ke roop mein dikhta hai.
Do metal rods — ek copper ki aur ek steel ki — ko ek saath garam paani mein daala gaya. Kaunsi rod ka doosra sira jaldi garam hoga aur kyun?
Copper rod ka doosra sira jaldi garam hoga, kyunki copper steel se better heat conductor hai — copper mein heat conduction ki rate zyada hoti hai. Yehi activity textbook mein different metals ki conductivity compare karne ke liye use hoti hai.
Exercise Questions — Solutions (Q1–Q6)
Q1. Fill in the blanks: (a) Heat flows from a body at ______ temperature to a body at ______ temperature. (b) In solids, heat transfer mainly happens by ______. (c) Liquids aur gases mein heat transfer ______ se hota hai. (d) Sun ki heat humtak ______ ke through pahunchti hai, jisme koi medium ki zaroorat nahi hoti.
(a) higher, lower (b) conduction (c) convection (d) radiation
Marking scheme: Har blank ka 0.5 mark — total 2 marks. Spelling galat ho par concept sahi ho to full marks milte hain.
Q2. Land breeze din mein banti hai ya raat mein? Reason ke saath samjhao.
Land breeze raat mein banti hai.
Raat ko zameen (land) samundar ke paani se zyada tezi se thandi hoti hai, kyunki zameen ki specific heat capacity paani se kam hoti hai. Isliye raat mein zameen ke upar ki hawa jaldi thandi ho jaati hai — yeh thandi, dense hawa neeche baithti hai aur zameen se samundar ki taraf bahti hai (kyunki samundar abhi bhi garam hai aur uske upar ki hawa halki hokar upar uthti hai). Zameen se samundar ki taraf chalne wali is hawa ko land breeze kehte hain.
Marking: Direction (1 mark) + correct reasoning with specific heat/convection logic (2 marks) = 3 marks.
Q3. Ek steel ka chammach garam chai mein rakha hai. Kuch der baad chammach ka handle bhi garam ho jaata hai — is process ka naam batao aur ek line mein samjhao.
Is process ko conduction (chaalan) kehte hain.
Chai ki heat se chammach ke molecules jo chai ko touch kar rahe hain, vibrate karna shuru karte hain aur apni energy adjacent molecules ko transfer karte hain — is tarah heat particle-se-particle handle tak pahunch jaati hai, bina kisi particle ke apni jagah chhode.
Marking: Correct term (1 mark) + explanation (1 mark) = 2 marks.
Q4. Thermos flask (vacuum flask) mein liquid ka temperature lambe samay tak maintain kyun rehta hai? Do reasons do.
(i) Thermos flask ki double wall ke beech vacuum hota hai — jisme koi matter nahi hota, isliye conduction aur convection dono practically zero ho jaate hain kyunki dono ko medium chahiye.
(ii) Andar ki wall par silvered (shiny) coating hoti hai jo radiation ko reflect kar deti hai — isse heat radiation ke through bhi bahar nahi nikal paati.
Isliye teeno modes (conduction, convection, radiation) block ho jaate hain aur liquid apni temperature der tak maintain karta hai.
Marking: Ek reason ka 1.5 mark — total 3 marks.
Q5. Ek activity design karo jisse yeh prove ho ki paani conduction ka bura conductor hai magar convection ka accha medium hai.
Activity: Ek test tube mein paani lo. Test tube ke neeche kuch barf ka tukda (ice) ek weight (jaise chhoti wire mesh) ke saath daal do taaki wo neeche hi rahe. Ab test tube ke upar wale hisse ko flame par garam karo.
Observation: Upar ka paani jaldi ubalne lagega (convection currents ban rahe hain — garam paani halka hokar upar rehta hai), lekin neeche wali barf bahut der tak nahi pighlegi — kyunki paani ke through heat conduction se neeche transfer nahi ho paati.
Conclusion: Yeh prove karta hai ki paani conduction ka bura conductor hai, jabki jab paani free tarike se move kar sake (jaise poore beaker mein garam karne par) to convection ke through heat achhe se transfer hoti hai.
Marking: Setup (1) + observation (1) + conclusion (1) = 3 marks.
Q6. Do numerical/conceptual example do jaha radiation ka use daily life mein dikhta hai, aur ek example do jaha radiation avoid karna zaroori hota hai.
Radiation ka use (daily life):
1. Sun se heat prithvi tak radiation se pahunchti hai (space mein vacuum hai, isliye conduction/convection possible nahi).
2. Solar cooker mein reflecting surface radiation ko concentrate karke khana pakati hai.
Radiation avoid karna zaroori: Garmi mein hum white/light-coloured kapde pehente hain kyunki wo radiation ko zyada reflect karte hain aur kam absorb karte hain — isse body zyada garam nahi hoti. Dark clothes radiation zyada absorb karte hain isliye garmi mein avoid kiye jaate hain.
Marking: Do uses (1+1) + avoid example with reasoning (1) = 3 marks.
Important Equations — Ek Nazar Me
| Concept | Rule / Statement | Example |
|---|---|---|
| Conduction | Heat transfer particle-se-particle, particles apni position nahi chhodte. Solids mein dominant. | Garam chai mein rakha steel chammach garam ho jaana |
| Convection | Heat transfer actual particles ke movement se. Liquids aur gases mein hota hai. | Paani boil hona, room heater se kamra garam hona |
| Radiation | Heat transfer bina kisi medium ke, electromagnetic waves ke through. | Sun ki heat vacuum se hoti hui Earth tak |
| Heat flow direction | Heat hamesha higher temperature se lower temperature ki taraf flow karta hai jab tak thermal equilibrium na aa jaaye | Garam cup se hath tak heat aana |
| Good conductors | Metals (silver, copper, aluminium) — free electrons ki wajah se | Cooking pan, tar |
| Insulators (bad conductors) | Wood, plastic, rubber, air, water (comparatively) — free electrons absent | Handle of utensils, thermocol |
| Sea breeze | Din mein: land garam > sea, hawa sea se land ki taraf bahti hai | Din ke coastal areas |
| Land breeze | Raat mein: land thanda > sea garam, hawa land se sea ki taraf bahti hai | Raat ke coastal areas |
| Dark vs light colours | Dark colours zyada radiation absorb karte hain; light colours zyada reflect karte hain | Garmi mein white kapde comfortable |
↔ Table ko side me swipe karein
Common Mistakes — Yahan Marks Kat te Hain
- Convection ko conduction samajh lena — yaad rakho: conduction mein particles apni jagah nahi chhodte, convection mein particles khud travel karte hain.
- Radiation ko sirf 'garmi' samajh lena — radiation electromagnetic waves hain, iske liye koi medium (solid/liquid/gas) zaroori nahi, yeh vacuum mein bhi travel karti hai.
- Sea breeze aur land breeze ki direction ulta likh dena — yaad rakho: din mein sea → land (sea breeze), raat mein land → sea (land breeze).
- Sochna ki paani achha heat conductor hai — actually paani conduction mein bura conductor hai, lekin convection ke through heat achhe se transfer karta hai.
- Thermos flask ke design mein sirf vacuum ka role likh dena aur silvered coating (jo radiation reflect karti hai) ka role bhool jaana — dono zaroori hain full marks ke liye.
- Dark aur light colour ka radiation absorption/reflection ulta likh dena — dark colours zyada absorb karte hain, light colours zyada reflect karte hain.
Board-Style Important Questions
- Explain why cooking utensils are usually made of metal but their handles are made of wood or plastic.
- With the help of a diagram, explain how land breeze and sea breeze are formed.
- Why does a thermos flask keep hot liquids hot and cold liquids cold for a long time?
- Design an activity to show that water is a poor conductor of heat.
- Why do people prefer wearing light-coloured clothes in summer and dark-coloured clothes in winter?
- State and explain the three modes of heat transfer with one example each.
Aksar Poochhe Jaane Wale Sawaal
Class 7 Science Chapter 7 'Heat Transfer in Nature' mein kaun kaun se main topics cover hote hain?
Is chapter mein heat transfer ke teen modes — conduction, convection aur radiation — detail mein cover hote hain. Iske saath land breeze aur sea breeze kaise banti hai, thermos flask ka design, garmi/sardi mein kapdon ka colour kyun matter karta hai, aur conductors vs insulators jaisi real-life applications bhi discuss hoti hain.
Conduction, convection aur radiation mein basic difference kya hai?
Conduction solids mein particle-se-particle heat transfer hai (medium zaroori hai, particles apni jagah nahi chhodte). Convection liquids/gases mein hota hai jisme heated particles khud move karke heat le jaate hain (medium zaroori hai). Radiation ke liye kisi medium ki zaroorat nahi hoti — yeh electromagnetic waves ke through hota hai, jaise Sun ki heat vacuum se hoti hui prithvi tak pahunchti hai.
Land breeze aur sea breeze mein kya farak hai?
Sea breeze din mein banti hai — zameen paani se jaldi garam hoti hai, isliye zameen ke upar ki garam hawa upar uthti hai aur samundar se thandi hawa zameen ki taraf bahti hai. Land breeze raat mein banti hai — is baar zameen jaldi thandi ho jaati hai aur zameen se samundar ki taraf hawa bahti hai. Yeh dono convection ka hi example hain.
Class 7 Science ki current NCERT book ka naam kya hai aur usme kitne chapters hain?
2026-27 session ki current rationalised NCERT Class 7 Science book ka naam 'Curiosity' hai, jisme total 12 chapters hain — yeh purani 13-chapter structure se reduce ki gayi hai. Kuch pehle wale chapters jaise Nutrition in Plants, Acids-Bases-Salts (separate chapter), Motion and Time, Electric Current and its Effects rationalised out ho chuke hain.
Exams ke liye is chapter se important questions kaunse type ke aate hain?
Class 7 Science heat transfer in nature ke important questions mostly conceptual reasoning type hote hain — jaise 'land breeze raat mein kyun banti hai', 'thermos flask liquid ko garam kaise rakhta hai', activity-based questions (paani mein conduction test), aur daily-life application questions (kapdon ka colour, cooking utensils ke materials). Diagram-based questions bhi common hain jisme convection current dikhani hoti hai.
Metals achhe heat conductor kyun hote hain?
Metals mein free electrons hote hain jo bahut fast move karte hain — yeh electrons heat energy ko bahut jaldi ek jagah se doosri jagah carry kar dete hain, isliye metals conduction ke through heat ko fast transfer karte hain. Yehi wajah hai ki cooking utensils steel/aluminium jaise metals ke bante hain, jabki unke handle plastic/wood (insulators) ke hote hain taaki haath na jale.
Class 7 Science — Saare Chapters
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