Jung aur Dahan
Class 7 Science · Chapter 5: Hamare Aas-paas Badlaav: Bhautik aur Rasaayanik · NCERT Curiosity section 5.3
Seekho
School ke paas ke purane lohe ke gate par parat-daar laal-bhoori tah hai. Neel thoda khurachta hai: ye ab loha nahi balki jung hai, ek naya padaarth jise iron oxide kehte. Loha hawa ki oxygen aur nami se kriya karta: jung lagna rasaayanik badlaav hai.
iron + oxygen (from air) + water → iron oxide (rust)
Teacher ke saath dost magnesium ribbon ko chimte se lau par pakadte hain. Wo chaundhiyaati safed roshni se jalta aur safed powder chhodta, magnesium oxide. Padaarth ka oxygen mein jalkar garmi aur roshni dena dahan hai. Lakdi, kaagaz, kerosene, LPG aur sooti kapda dahansheel; patthar aur kaanch nahi.
magnesium + oxygen → magnesium oxide + heat + light
Meher jalti mombatti par kaanch ka gilaas dhakti hai: jaldi lau bujh jaati, kyunki oxygen khatam. Dahan ko teen cheezein saath chahiye, fire triangle: eendhan, oxygen, aur itni garmi ki eendhan ka prajvalan taapmaan (sabse kam taapmaan jis par aag pakde) aa jaaye. Magnifying glass se kendrit dhoop bhi kaagaz ko us had tak garam kar sakti hai.
Aag bujhaane ke liye triangle ki ek bhuja hatao: paani thanda karta, ret ya kambal hawa rokte, aur gas ka knob band karna eendhan hataata. Agar kisi ke kapdon mein aag lage to mote sooti kambal mein lapeto, synthetic kabhi nahi. Kuch jeev, jaise jugnu, lagbhag bina garmi ke rasaayanik badlaav se roshni banaate: bioluminescence.
Jalti mombatti dono tarah ke badlaav dikhaati. Mom pighalna, baati mein chadhna aur bhaap banna bhautik; bhaap ka jalkar carbon dioxide, garmi aur roshni dena rasaayanik. Ek mashhoor vaigyaanik ne sirf mombatti ke vigyaan par poori vyaakhyaan-maala di thi!
Explore: mombatti ki lau ka safar.
- Steps kram mein lagao.
Yaad rakho
- Jung se iron oxide; magnesium jalne se magnesium oxide: dono rasaayanik.
- Fire triangle: eendhan, oxygen aur garmi (prajvalan taapmaan); ek hatao to aag band.
Quick check
Chhoti aag par ret daalne se wo bujhti mukhyatah kyunki ret …
- hawa (oxygen) rok deti
- eendhan hai
- taapmaan badhaati
- carbon dioxide banaati
Answer
hawa (oxygen) rok deti. Oxygen ke bina dahan nahi chal sakta.
Socho
Maachis ki teeli dibbi par ragadne se kyun jalti, par yun hi rakhne par nahi?
Ek answer
Ragadne se itni garmi banti ki teeli ka sira prajvalan taapmaan tak pahunche. Pade rehne par itna garam nahi hota.
Practice
Teen levels (easy, medium, hard) ke naye sawaalon se practice karo, kuch hands-on, hints aur hal ke saath. Topic poora karne ke liye pichhle 5 mein se 4 sahi karo.