Class 7 Science Chapter 7: Heat Transfer in Nature (Hinglish Notes)

Kuch jagah zyaada garam kyun lagti hain

Chapter Gangtok se shuru hota hai, jahan Pema aur uska bhai Palden sardi ki shaam aag ke paas baithe hain. Palden abhi Kerala se lauta hai, jo sardi mein bhi garam aur nam laga. Kerala equator ke zyaada paas hai aur uska samudri kinaara lamba hai, aur Dharti ke liye garmi ka mukhya srot Sooraj hai. Daadi ko dhaatu ki kadaahi mein thukpa banaate dekh kar wo sochte hain ki bartan dhaatu ke kyun hote hain. Jawab garmi ke chalne ke tareekon mein hai.

Conduction

Dhaatu ki patti par mom se pins chipka kar uska ek sira garam karo (Activity 7.1): pins ek-ek karke girti hain, sabse paas waali pehle. Garmi patti mein garam sire se thande sire ki taraf chalti hai: har kan apne padosi ko garmi deta hai, par kan apni jagah se nahi hilte. Ye conduction hai, thos cheezon mein garmi chalne ka mukhya tareeka.

Jo cheezein garmi ko aasaani se guzarne deti hain, jaise dhaatu, wo achhe conductor hain, isliye hum dhaatu ke bartanon mein pakaate hain. Lakdi, kaanch, mitti aur porcelain kharaab conductor yaani insulator hain, isliye mitti ya porcelain ke cup mein chai der tak garam rehti hai. Hawa bhi kharaab conductor hai. Oon ke kapde apne chhedon mein hawa rokte hain, do patli razaaiyon ke beech hawa ki parat hoti hai, aur kuch ghar hollow bricks ya mitti aur gobar bhari do lakdi ki parton waali deewaron se garmi aur sardi rokte hain, jaise Uttarkashi ke Mori block mein.

Convection

Mombatti ke upar latka kaagaz ka cup upar uthta hai (Activity 7.2), kyunki andar ki hawa garam hokar phailti hai, halki hoti hai aur upar jaati hai. Dhuaan bhi isi wajah se uthta hai. Neeche se garam kiye paani mein (Activity 7.3) rangeen dhaara beech se upar uthti hai aur kinaaron se neeche aati hai: garam paani upar, thanda paani uski jagah. Liquid ya gas ke kanon ke asal mein chalne se garmi ka jaana convection hai. Aur padho conduction, convection aur radiation mein.

Sea breeze aur land breeze

Dhoop mein mitti paani se jaldi garam hoti hai, aur jaldi thandi bhi (Activity 7.4). Isliye din mein zameen ke upar ki garam hawa uthti hai aur samudra se thandi hawa aati hai: sea breeze. Raat mein zameen pehle thandi hoti hai, samudra ke upar ki garam hawa uthti hai, aur zameen se samudra ki taraf land breeze chalti hai. Aur padho land breeze aur sea breeze mein.

Radiation

Aag se jo garmi mehsoos hoti hai, aur Dharti par Sooraj ki garmi, radiation se aati hai, jise kisi medium ki zaroorat nahi. Har cheez garmi radiate karti hai, isiliye garam bartan apne aap thanda ho jaata hai. Halke rang ke kapde apne upar padne waali zyaadatar garmi lauta dete hain, isliye garmi mein theek hain; gehre rang zyaada garmi sokhte hain aur sardi mein theek hain. Bartan mein paani garam karte samay teeno saath hote hain: bartan conduction se, paani convection se garam hota hai, aur garmi hum radiation se mehsoos karte hain. Oonche Himalaya mein lohe ka chulha bukhari teeno tareekon se khaana bhi pakaata hai aur kamra bhi garam karta hai.

Water cycle aur groundwater

Sooraj ki garmi samudron, nadiyon aur jheelon ka paani bhaap banaati hai, aur paudhe transpiration se bhaap chhodte hain. Upar uthti bhaap thandi hokar baadal banti hai, jo baarish, barf aur ole laate hain: precipitation. Ye water cycle paani ko jagah-jagah pahunchata hai aur Dharti par paani ki kul maatra ek jaisi rakhta hai. 6th century CE mein Ujjaini ke Varahamihira ne apni kitaab Brihatsamhita mein mausam ki baarish ka andaaza lagaane ke tareeke bataaye.

Kuch baarish ka paani zameen mein risata hai: gravel se sabse tez, ret se dheere aur clay se sabse dheere (Activity 7.5). Ye infiltration aquifers mein groundwater jama karta hai, jise kuen aur borewell nikaalte hain. Groundwater jitna bharta hai usse tez khatm ho raha hai, isliye rainwater harvesting, recharge pits aur Ladakh ke ice stupa paani bachaane mein madad karte hain. Aur padho water cycle aur groundwater mein.

Har sawaal ka jawab Chapter 7 ke NCERT solutions mein hai.