Temperature, Pressure aur Density
Kya density hamesha ek jaisi rehti hai? Garam karo, thanda karo, ya dabao: dekhte hain density ke saath kya hota hai! 🌡️🎈
🧭 Is Post Mein
📖 Kahani: Jamaa Ghee Doob Kyun Gaya?
Disambar ki thandi subah thi. Priya ki Mummy ne jama hua ghee garam karne ke liye stove par rakha. Thoda ghee pighal gaya, par ek bada sa jama hua tukda abhi bhi bacha tha.
Golu ne dhyaan se dekha: “Arre! Jama hua tukda toh pighle ghee mein neeche baith gaya! Par barf toh paani mein tairti hai. Ghee ulta kyun kar raha hai?”
Tabhi khidki se Rohan chillaya, “Dekho, mele wala garam hawa ka gubbara upar ja raha hai! Neeche aag jal rahi hai.”
Priya sochne lagi: “Ghee wahi hai, hawa bhi wahi hai. Bas taapmaan (temperature) badla hai. Toh kya garam ya thanda karne se density badal jaati hai?” 🤔
Aaj ka post isi sawaal ka jawaab dega. Ghee aur barf ki ulti kahani ka raaz Examples mein khulega! 🔍
🎯 Is Post Mein Kya Seekhenge
- Garam karne par zyaadatar cheezein failti (expand) kyun hain, aur isse density kam kyun hoti hai
- Thanda karne par cheezein sikudti (contract) hain aur density badhti hai
- Gas ki density par pressure (dabaav) ka asar: dabao toh density badhti hai
- Solid aur liquid par pressure ka asar bahut kam kyun hota hai
- Paani ka anokha vyavhaar: 4°C par sabse zyada density, aur barf paani par kyun tairti hai
- Garam hawa ka gubbara, sardi mein jheel, LPG cylinder jaise real life udaharan
🧱 Basics: Pehle Yeh Aana Chahiye
1. Density = Mass ÷ Volume. Mass wahi rahe aur volume badh jaaye, toh density ghatti hai. Volume ghat jaaye, toh density badhti hai.
2. Kan (particles): har padarth bahut chhote kanon se bana hai. Kan hamesha hilte rehte hain, aur unke beech thodi khaali jagah hoti hai.
3. Temperature: kitna garam ya thanda hai, uska naap (°C mein). Garam karne par kan tez hilte hain.
4. Pressure (dabaav): kisi cheez par kitni zor se dabaya ja raha hai. Cycle ke pump se tyre mein hawa bharna dabaav ka udaharan hai.
💡 Concept: Density Badalti Kyun Hai?
Step 1: Mass nahi badalta. Ek katori ghee ko garam karo ya thanda, uske kan utne hi rehte hain. Na koi kan aaya, na gaya. Isliye mass same rehta hai.
Step 2: Volume badal sakta hai. Garam karne par kan zyada tez hilte hain aur ek-doosre se thoda door-door rehne lagte hain. Isliye cheez thodi fail jaati hai (volume badhta hai). Thanda karne par kan paas aa jaate hain, cheez sikud jaati hai (volume ghatta hai).
Step 3: Density ka hisaab. Density = Mass ÷ Volume. Mass same, volume bada, toh density chhoti. Mass same, volume chhota, toh density badi.
Kyun? Socho 10 laddoo ek chhoti thaali mein thase hue hain, phir wahi 10 laddoo badi thaali mein phaila diye. Laddoo utne hi hain (mass same), par jagah zyada hai, toh “ek jagah par kitne laddoo” kam ho gaye. Yahi density ka ghatna hai!
🌡️ Temperature ka asar
- Solid: garam karne par thoda sa failte hain, density thodi kam hoti hai. Badlav chhota hota hai, jaise lohe ki patri garmi mein kuch millimetre lambi ho jaati hai.
- Liquid: solid se zyada failte hain. Garam paani thande paani se thoda halka (kam density wala) hota hai, isliye garam paani upar aata hai.
- Gas: sabse zyada failti hai. Garam hawa ki density thandi hawa se kaafi kam hoti hai, isliye garam hawa upar uthti hai.
Gas sabse zyada kyun failti hai? Gas ke kan pehle se hi bahut door-door hote hain aur unhe baandhne wala khinchaav bahut kamzor hota hai. Garmi milte hi woh aur door bhaagte hain.
🗜️ Pressure ka asar
- Gas: gas ke kanon ke beech bahut khaali jagah hoti hai, isliye dabaane par gas aasaani se dab jaati (compress) hai. Volume ghatta hai, mass wahi, toh density badh jaati hai. Jaise taapmaan same rakh kar dabaav doguna karo, toh volume lagbhag aadha aur density lagbhag doguni ho jaati hai.
- Liquid aur solid: kan pehle se hi paas-paas hote hain. Bahut zor se dabaane par bhi volume lagbhag nahi badalta. Isliye roz ki zindagi mein inki density par pressure ka asar na ke barabar maana jaata hai.
🧊 Paani ka anokha vyavhaar
Step 4: Zyaadatar liquid thande hone par sikudte hi jaate hain. Paani bhi 4°C tak sikudta hai, isliye 4°C par paani ki density sabse zyada (lagbhag 1 g/cm³) hoti hai. Par 4°C se neeche, 0°C tak, paani ulta failne lagta hai. Aur jab barf banti hai toh volume lagbhag 9% badh jaata hai. Isliye barf ki density lagbhag 0.92 g/cm³ hoti hai, paani se kam, aur barf paani par tairti hai.
Kyun? Barf bante samay paani ke kan ek khaas jaali (pattern) mein jud jaate hain jisme beech mein khaali jagah reh jaati hai. Isliye barf mein kan “dheele” baithe hote hain.
Ek line mein: garam karo toh (zyaadatar) density ghatti hai, thanda karo toh badhti hai; gas ko dabao toh density badhti hai; aur paani 4°C par sabse bhaari hota hai! 🎯
🖼️ Diagrams: Picture se Samjho
🔐 Deep Concept: Thoda Gehraai Mein
1. Isliye density ke saath taapmaan likhte hain: kyunki density taapmaan ke saath badalti hai, vaigyanik table mein likhte hain “paani ki density 4°C par 1.000 g/cm³”. 20°C par yeh lagbhag 0.998 aur 80°C par lagbhag 0.972 g/cm³ hoti hai. Farq chhota hai, par sahi naap ke liye zaroori hai.
2. Gas mein dabaav aur volume ka rishta: taapmaan same rahe toh gas ka dabaav jitne guna badhao, volume utne hi guna ghatta hai (lagbhag). Dabaav 2 guna → volume ½ → density 2 guna. Dabaav 3 guna → density lagbhag 3 guna.
3. Sardi mein jheel kaise bachti hai: sardi mein upar ka paani thanda hokar 4°C tak bhaari hota hai aur neeche chala jaata hai. Jab poori jheel 4°C par aa jaati hai, toh upar ka paani aur thanda hokar halka rehta hai aur upar hi barf ban jaata hai. Barf ki parat ek “kambal” ki tarah kaam karti hai. Neeche lagbhag 4°C ka paani bacha rehta hai, aur machhliyaan zinda rehti hain! 🐟
4. Convection (sanvahan): kisi bartan mein neeche se garam karne par neeche ka liquid garam hokar halka ho jaata hai aur upar uthta hai; upar ka thanda, bhaari liquid neeche aata hai. Is ghoomte bahaav se poora liquid garam hota hai. Yeh density badalne ka hi kamaal hai.
5. Ghee ka raaz: zyaadatar padarth (jaise ghee, mom, naariyal tel) jamne par sikudte hain, isliye unka jama roop pighle roop se zyada ghana hota hai aur usme doob jaata hai. Paani isme ek khaas apvaad (exception) hai.
✏️ Examples: Hisaab Lagao
⚖️ Difference Table: Solid, Liquid aur Gas par Asar
| Padarth | Garam karne par | Dabaav badhane par | Udaharan |
|---|---|---|---|
| Solid | Bahut thoda failta hai; density thodi kam | Lagbhag koi asar nahi | Patri mein garmi ke liye gap |
| Liquid | Solid se zyada failta hai; density kam | Bahut hi kam asar | Thermometer mein liquid ka chadhna |
| Gas | Sabse zyada failti hai; density kaafi kam | Aasaani se dabti hai; density badhti hai | Garam hawa ka gubbara, LPG cylinder |
| Paani (khaas) | 0°C se 4°C tak sikudta hai, phir failta hai | Bahut kam asar | Barf tairti hai, jheel upar se jamti hai |
🚫 Misconceptions (Galat Dhaarnaayein)
✅ Sahi: Mass same rehta hai. Sirf volume badalta hai, isliye density badalti hai.
✅ Sahi: Garam hawa failkar kam density wali ho jaati hai; aas-paas ki bhaari thandi hawa neeche aakar use upar dhakel deti hai.
✅ Sahi: Paani sirf 4°C tak bhaari hota hai. 4°C se neeche halka hone lagta hai, aur barf paani se halki hoti hai.
✅ Sahi: Gas par pressure ka bada asar hota hai. Solid aur liquid par asar itna kam hai ki roz ki zindagi mein ise lagbhag nahi maana jaata.
✅ Sahi: Ek hi taapmaan aur dabaav par yeh tay hai. Taapmaan ya dabaav badlo toh density badal sakti hai.
🔤 Key Terms (Exam mein English shabd hi likhna)
❓ FAQs
1. Garam karne par density kam kyun hoti hai?
Garam karne par kan tez hilte hain aur door-door ho jaate hain, toh volume badhta hai. Mass same rehta hai, isliye Mass ÷ Volume chhota ho jaata hai.
2. Kya solid ki density bhi taapmaan se badalti hai?
Haan, par bahut thodi. Solid ke kan mazbooti se bandhe hote hain, isliye woh bahut kam failte hain.
3. Barf paani mein kyun tairti hai?
Jamte samay paani failta hai, isliye barf ki density (lagbhag 0.92 g/cm³) paani (lagbhag 1 g/cm³) se kam hoti hai. Kam density wali cheez tairti hai.
4. Gas ko dabaane par density kyun badhti hai?
Gas ke kanon ke beech bahut khaali jagah hoti hai. Dabaane par woh paas aa jaate hain, volume ghatta hai, mass wahi rehta hai, toh density badhti hai.
5. LPG cylinder mein itni gas kaise aa jaati hai?
Bahut zyada dabaav daal kar gas ko itna dabaaya jaata hai ki woh liquid ban jaati hai. Iski density bahut badh jaati hai, isliye chhote cylinder mein bahut saara bhar jaata hai.
6. Sabse zyada density par paani kis taapmaan par hota hai?
Lagbhag 4°C par.
🧪 Activity: Bottle par Gubbara, Garam aur Thanda Paani
Saamaan: ek khaali, sookhi plastic ya kaanch ki bottle (patli gardan wali), ek gubbara (balloon), do bade bartan, ek mein gungunaa garam paani (nal ke garam paani jitna, ubalta hua nahi), doosre mein barf wala thanda paani.
Kya dikhega: garam paani mein gubbara phoolkar seedha khada ho jaata hai. Thande paani mein woh pichak jaata hai, kabhi-kabhi thoda bottle ke andar bhi khinch jaata hai.
Nishkarsh: bottle ki hawa garam hokar faili (volume badha), toh woh gubbare mein bhar gayi. Hawa ka mass wahi tha, volume badha, toh density kam hui. Thanda karne par hawa sikudi, volume ghata, density badhi.
🤔 Socho: kya garam karne par bottle mein naya hawa aa gayi thi?
Nahi. Munh par gubbara chadha tha, toh bahar se hawa andar nahi aa sakti thi. Wahi hawa (wahi mass) bas fail gayi. Isliye yeh activity saaf dikhati hai ki mass same rehte hue sirf volume (aur isliye density) badla.
Yeh activity NCERT ki Class 8 Science book Curiosity (Chapter 9) ke taapmaan aur density wale hisse par aadharit hai, aur yahan apne shabdon mein samjhayi gayi hai.
🏠 Mini Experiments (Ghar pe)
🧠 Think Like a Scientist
Sawaal: Rohan kehta hai, “Garam paani aur thanda paani ek jaise hain, ek-doosre mein turant mil jaate hain.” Priya kehti hai, “Nahi, garam paani upar tairta hai.” Kaun sahi hai?
Scientist ka tareeka dekho
1. Observe (dekho): nahaate waqt baalti mein garam paani daalo toh upar ka paani zyada garam lagta hai.
2. Guess (anumaan): garam paani ki density kam hai, toh woh upar rehna chahiye.
3. Test (jaanch): ek glass mein thanda paani, usme neeche dropper se rangeen garam paani chhodo (Mini Experiment 1).
4. Result (nateeja): rangeen garam paani upar uthkar sabse upar parat bana leta hai; dheere-dheere hi mil paata hai.
5. Conclusion (nishkarsh): Priya sahi hai. Garam paani ki density thande paani se thodi kam hoti hai, isliye woh upar uthta hai. Kuch der baad dono ka taapmaan barabar hone par woh poori tarah mil jaate hain.
🌍 Real Life Mein
- Garam hawa ka gubbara: burner andar ki hawa garam karta hai, density kam hoti hai, aur gubbara upar uthta hai. Burner band karo toh hawa thandi hokar gubbara neeche aata hai.
- Jami hui jheel: pahaadon ki jheelein upar se jamti hain, neeche paani bacha rehta hai, jisse machhliyaan zinda rehti hain.
- Rail ki patri aur pul: garmi mein lohe ke failne ke liye beech mein chhota gap chhoda jaata hai.
- LPG cylinder, oxygen cylinder: gas ko bahut dabaav se dabaakar kam jagah mein zyada bhara jaata hai.
- Cycle ka tyre: pump se hawa dabaakar bhari jaati hai, isliye tyre sakht ho jaata hai.
- Kamre ka AC aur heater: AC aksar upar lagaya jaata hai (thandi bhaari hawa neeche aati hai), heater neeche rakha jaata hai (garam halki hawa upar jaati hai).
- Freezer mein bhari bottle: paani bhari kaanch ki bottle freezer mein phat sakti hai, kyunki barf banne par paani failta hai.
🔁 Recap: Poora Post Ek Nazar Mein
- Garam ya thanda karne par mass nahi badalta, volume badalta hai, isliye density badalti hai.
- Garam karo → failna (expansion) → density kam. Thanda karo → sikudna (contraction) → density zyada.
- Failna: gas > liquid > solid.
- Gas ko dabao → volume kam → density zyada. Solid aur liquid par dabaav ka asar bahut kam.
- Paani: 4°C par sabse zyada density; barf (~0.92 g/cm³) paani se halki, isliye tairti hai.
- Garam hawa ka gubbara, jheel ka upar se jamna, LPG cylinder: sab density ke badlav ke kamaal hain.
✍️ Fill in the Blanks
- Garam karne par zyaadatar padarth ______ hain aur unki density kam hoti hai.
- Garam ya thanda karne par padarth ka ______ nahi badalta.
- Paani ki density lagbhag ______ °C par sabse zyada hoti hai.
- Dabaav badhane par ______ ki density sabse zyada badhti hai.
- Barf ki density paani se ______ hoti hai, isliye woh tairti hai.
- Garam hawa ki density thandi hawa se ______ hoti hai.
Answers
1) failte (expand) · 2) mass · 3) 4 · 4) gas · 5) kam · 6) kam
✅ True / False
- Garam karne par paani ka mass badh jaata hai.
- Gas ko dabaane par uski density badhti hai.
- 0°C par paani ki density sabse zyada hoti hai.
- Solid ki density par dabaav ka asar bahut kam hota hai.
- Ghee jamne par failta hai, isliye jama ghee pighle ghee par tairta hai.
- Garam hawa ka gubbara isliye udta hai kyunki andar ki hawa ki density bahar ki hawa se kam hai.
Answers (kyun ke saath)
1) False: mass same rehta hai, sirf volume badalta hai.
2) True: volume ghatta hai, mass wahi, toh density badhti hai.
3) False: sabse zyada density lagbhag 4°C par hoti hai.
4) True: solid ke kan pehle se paas hote hain, dabte nahi.
5) False: ghee jamne par sikudta hai, toh jama ghee zyada ghana hokar doobta hai.
6) True: garam hawa failkar halki ho jaati hai aur upar uthti hai.
🔘 MCQs
Q1. Garam karne par kisi liquid ka kya hota hai? (a) Mass badhta hai (b) Volume badhta hai, density ghatti hai (c) Volume ghatta hai, density badhti hai (d) Kuch nahi badalta
✅ (b): garmi se kan door hote hain, volume badhta hai, density ghatti hai.
(a) mass kabhi nahi badalta, kan utne hi rehte hain.
(c) yeh thanda karne par hota hai.
(d) galat, volume aur density badalte hain.
Q2. Kiski density par dabaav ka sabse zyada asar hota hai? (a) Lohe (b) Paani (c) Hawa (d) Lakdi
✅ (c) Hawa: gas ke kanon ke beech bahut khaali jagah hai, isliye woh aasaani se dabti hai.
(a) lohe ke kan bahut paas, lagbhag nahi dabta.
(b) paani liquid hai, bahut kam dabta hai.
(d) lakdi solid hai, dabaav ka asar bahut kam.
Q3. Paani ki density kis taapmaan par sabse zyada hoti hai? (a) 0°C (b) 4°C (c) 37°C (d) 100°C
✅ (b) 4°C: 4°C tak paani sikudta hai, uske neeche failne lagta hai.
(a) 0°C par paani 4°C se thoda halka hai, aur barf toh aur halki.
(c) 37°C par paani fail chuka hota hai, density kam.
(d) 100°C par paani kaafi faila hota hai, density aur kam.
Q4. 100 g paani 80°C par 102.9 cm³ jagah leta hai. Uski density lagbhag? (a) 1.03 g/cm³ (b) 0.97 g/cm³ (c) 2.9 g/cm³ (d) 202.9 g/cm³
✅ (b) 0.97 g/cm³: 100 ÷ 102.9 ≈ 0.972.
(a) 1.03 = 102.9 ÷ 100; formula ulta.
(c) 2.9 = 102.9 − 100; ghatana galat.
(d) 202.9 = jodna galat.
Q5. Barf paani par kyun tairti hai? (a) Barf ka mass zyada hai (b) Barf mein hawa bhari hoti hai (c) Barf ki density paani se kam hai (d) Barf thandi hai isliye
✅ (c): jamne par paani failta hai, isliye barf (~0.92) paani (~1.00) se halki hai.
(a) zyada mass hone se toh doobti.
(b) saaf barf mein bhi tairna hota hai; asli kaaran kanon ki dheeli jaali hai.
(d) sirf thanda hona kaaran nahi; jama ghee bhi thanda hai par doobta hai.
Q6. 40 mL hawa (mass 0.048 g) ko dabaa kar 20 mL kiya. Nayi density? (a) 0.0012 g/mL (b) 0.0006 g/mL (c) 0.0024 g/mL (d) 0.0048 g/mL
✅ (c) 0.0024 g/mL: 0.048 ÷ 20 = 0.0024.
(a) yeh dabaane se pehle ki density (0.048 ÷ 40) hai.
(b) volume ko doguna maan liya (0.048 ÷ 80).
(d) 0.048 ÷ 10; volume galti se 10 mL maan liya.
Q7. Rail ki patri ke beech chhota gap kyun chhoda jaata hai? (a) Paani nikalne ke liye (b) Garmi mein lohe ke failne ke liye (c) Lohe ki bachat ke liye (d) Awaaz kam karne ke liye
✅ (b): garmi mein lohe failta hai; gap na ho toh patri tedhi ho sakti hai.
(a) paani nikalna iska kaaran nahi.
(c) bachat ke liye nahi, suraksha ke liye.
(d) gap se toh “khat-khat” awaaz aati hai, kam nahi hoti.
Q8. Sardi mein jheel ke neeche machhliyaan kyun zinda rehti hain? (a) Neeche ka paani ubalta hai (b) Upar barf ki parat banti hai aur neeche lagbhag 4°C ka paani bacha rehta hai (c) Machhliyaan barf kha leti hain (d) Poori jheel jam jaati hai
✅ (b): 4°C ka bhaari paani neeche rehta hai, barf upar tairti hai aur kambal ki tarah garmi rokti hai.
(a) neeche ka paani thanda hai, ubalta nahi.
(c) yeh kaaran nahi hai.
(d) aam taur par poori jheel nahi jamti, isi wajah se machhliyaan bachti hain.
🔗 Assertion–Reason
Options: (a) A aur R dono sahi, aur R, A ko samjhata hai · (b) A aur R dono sahi, par R, A ko nahi samjhata · (c) A sahi, R galat · (d) A galat, R sahi
1. A: Garam hawa ka gubbara upar uthta hai. R: Garam karne par hawa failti hai aur uski density kam ho jaati hai.
✅ (a): dono sahi, aur R hi A ka kaaran hai.
2. A: Gas ko aasaani se dabaaya ja sakta hai. R: Paani ki density 4°C par sabse zyada hoti hai.
✅ (b): dono baatein sahi, par R ka A se koi lena-dena nahi. A ka asli kaaran: gas ke kanon ke beech bahut khaali jagah.
3. A: Garam karne par lohe ki gend ka mass badh jaata hai. R: Garam karne par lohe ki gend failti hai.
✅ (d): A galat hai, mass same rehta hai. R sahi hai, gend thoda failti hai.
📝 Very Short Answer (1 mark)
1. Garam karne par density kam hoti hai ya zyada?
Zyaadatar padarthon mein kam hoti hai.
2. Kis taapmaan par paani sabse ghana (dense) hota hai?
Lagbhag 4°C.
3. Solid, liquid, gas mein se kaun sabse aasaani se dabta hai?
Gas.
4. Barf ki density lagbhag kitni hai?
Lagbhag 0.92 g/cm³.
5. Garam karne par padarth ki kaun si cheez same rehti hai: mass ya volume?
Mass.
🗒️ Short Answer (2–3 marks)
1. Garam karne par density kyun ghatti hai? Kanon ki madad se samjhao.
Garmi milne par kan tez hilte hain aur ek-doosre se door ho jaate hain, isliye volume badhta hai. Kan utne hi rehte hain, toh mass same rehta hai. Density = Mass ÷ Volume; volume bada hone se density chhoti ho jaati hai.
2. Gas par dabaav ka asar solid se zyada kyun hota hai?
Gas ke kanon ke beech bahut zyada khaali jagah hoti hai, toh dabaane par woh paas aa jaate hain aur volume kaafi ghatta hai. Solid ke kan pehle se hi bilkul paas-paas hote hain, toh dabaane ki jagah hi nahi hoti.
3. Paani bhari kaanch ki bottle freezer mein kyun phat sakti hai?
Paani jamkar barf banne par lagbhag 9% fail jaata hai. Bottle mein itni extra jagah nahi hoti, toh failti barf kaanch par zor lagaati hai aur bottle phat sakti hai.
4. AC kamre mein upar kyun lagaya jaata hai?
AC se nikli thandi hawa ki density zyada hoti hai, toh woh neeche aati hai, aur neeche ki garam halki hawa upar jaati hai. Is tarah poora kamra jaldi thanda hota hai.
📜 Long Answer (5 marks)
1. Temperature aur pressure ka solid, liquid aur gas ki density par kya asar hota hai? Udaharan ke saath samjhao.
Temperature: garam karne par kan door hote hain aur padarth failta hai; mass same rehta hai, isliye density ghatti hai. Thanda karne par ulta. Failna gas mein sabse zyada, liquid mein kam, solid mein sabse kam hota hai. Udaharan: garam hawa ka gubbara (gas), thermometer mein liquid ka chadhna (liquid), rail ki patri ke gap (solid).
Pressure: gas ke kanon ke beech khaali jagah zyada hai, toh dabaav badhane par volume ghatta hai aur density badhti hai (jaise LPG cylinder, tyre). Solid aur liquid lagbhag nahi dabte, toh unki density par dabaav ka asar na ke barabar hai.
Nishkarsh: isliye kisi padarth ki density batate waqt taapmaan (aur gas ke liye dabaav) bhi batana chahiye.
2. Paani ka anokha vyavhaar kya hai? Jheel mein jaliya jeevon ke liye yeh kaise faydemand hai?
Zyaadatar liquid thande hone par sikudte jaate hain, par paani sirf 4°C tak sikudta hai. 4°C se 0°C tak paani failta hai, aur barf banne par aur zyada failta hai. Isliye paani ki density 4°C par sabse zyada hoti hai aur barf (~0.92 g/cm³) paani par tairti hai.
Jheel mein: sardi mein upar ka paani 4°C tak thanda hokar neeche jaata hai. Jab saara paani 4°C par aa jaata hai, toh upar ka paani aur thanda hokar halka rehta hai aur upar hi jam jaata hai. Barf ki parat neeche ke paani ko thand se bachaati hai. Neeche lagbhag 4°C ka paani rehta hai, jisme machhliyaan aur doosre jeev zinda reh paate hain.
📰 Case-Based Question
Q1. Burner andar ki hawa ki density par kya asar daalta hai?
Hawa garam hokar failti hai, toh uski density kam ho jaati hai.
Q2. Gubbara upar kyun uthta hai?
Andar ki garam hawa bahar ki thandi hawa se halki (kam density) hoti hai, isliye bahar ki bhaari hawa use upar dhakelti hai.
Q3. Dopahar mein hawa ko zyada garam kyun karna pada?
Dopahar mein bahar ki hawa bhi garam thi, yaani uski density pehle se kam thi. Andar aur bahar ki density mein utna hi farq laane ke liye andar ki hawa ko aur zyada garam karna pada.
Q4. Burner dheema karne par gubbara neeche kyun aaya?
Andar ki hawa thandi hokar sikudi, density badh gayi aur bahar ki hawa ke kareeb aa gayi, isliye gubbara neeche aane laga.
🚀 HOTS (Socho Zara Gehra)
1. Ek mom (wax) ka tukda pighli mom mein daalo, aur ek barf ka tukda paani mein. Dono mein kya farq dikhega aur kyun?
Mom ka tukda doobega, kyunki mom jamne par sikudta hai aur jama mom ghana hota hai. Barf tairegi, kyunki paani jamne par failta hai. Paani is maamle mein apvaad (exception) hai.
2. Agar barf paani se bhaari hoti, toh sardi mein jheel ka kya hota?
Barf banti aur doob jaati, phir upar naya paani jamta aur doobta. Dheere-dheere jheel neeche se upar tak poori jam sakti thi, aur zyaadatar jaliya jeev mar jaate.
3. Ek band, aadhi bhari plastic bottle ko pahaad se neeche laane par woh pichak jaati hai. Kyun?
Pahaad par hawa ka dabaav kam hota hai, toh bottle band karte waqt andar kam dabaav wali hawa thi. Neeche aane par bahar ka dabaav zyada hai, jo bottle ko daba deta hai; andar ki hawa dab kar kam volume leti hai, aur uski density badh jaati hai.
🏆 Olympiad Level
1. 1 L hawa ka mass 1.2 g hai. Garam karne par woh 1.5 L ho jaati hai. Nayi density g/L mein? (a) 1.8 (b) 0.8 (c) 1.25 (d) 0.6
✅ (b) 0.8 g/L: mass same 1.2 g; 1.2 ÷ 1.5 = 0.8.
(a) 1.2 × 1.5, guna galat. (c) 1.5 ÷ 1.2, ulta. (d) 1.2 ÷ 2, galat volume.
2. Taapmaan same rakhte hue ek gas ka dabaav 3 guna kar diya. Uski density lagbhag? (a) Same rahegi (b) 3 guna (c) 1/3 (d) 9 guna
✅ (b) 3 guna: dabaav 3 guna → volume lagbhag 1/3 → mass same, density 3 guna.
(a) gas dabti hai, density badalti hai. (c) yeh volume ka badlav hai, density ka nahi. (d) density dabaav ke saath seedhe anupaat mein badhti hai, varg (square) mein nahi.
3. 0°C par 1 kg barf ka volume lagbhag 1090 cm³ hai. Pighalne par 0°C ke paani ka volume lagbhag 1000 cm³. Volume kitne % ghata?
Ghataav = 1090 − 1000 = 90 cm³. Pratishat = 90 ÷ 1090 × 100 ≈ 8.3%. (Dhyaan do: paani se barf banne par badhna 90 ÷ 1000 = 9% hai, par barf se paani banne par ghatna 8.3%, kyunki aadhar alag hai.)
Har option pe tap karo, turant pata chalega sahi ya galat.
Q1. 200 gram water ka volume 20°C pe 200.4 cm³ aur 80°C pe 205.8 cm³ hai. 80°C pe water ka mass kitna?
(a) 205.8 gram
❌ Galat: Volume ko mass maan liya (205.8). Mass same rehta hai: 200.
(b) 194.6 gram
❌ Galat: Volume badhne pe mass subtract kiya: 200 − 5.4 = 194.6. Mass same: 200.
(c) 200 gram
✅ Sahi! Heat karne pe mass nahi badalta, sirf volume badhta hai. Mass = 200 gram.
(d) 205.4 gram
❌ Galat: Volume ka badhna mass mein add kiya: 200 + 5.4 = 205.4. Mass same: 200.
Q2. Ek gas ki density 1.2 kg per cubic metre hai. Temperature same rakh ke pressure double kiya, to volume lagbhag half ho gaya. Ab density lagbhag kitni?
(a) 0.6 kg per cubic metre
❌ Galat: Volume ki tarah density bhi half kar di: 1.2 ÷ 2 = 0.6. Volume kam, density zyada: 1.2 × 2 = 2.4.
(b) 1.2 kg per cubic metre
❌ Galat: Density same maani (1.2). Gas compress hone pe density badhti hai: 1.2 × 2 = 2.4.
(c) 3.2 kg per cubic metre
❌ Galat: Double ki jagah 2 add kiya: 1.2 + 2 = 3.2. Sahi: 1.2 × 2 = 2.4.
(d) 2.4 kg per cubic metre
✅ Sahi! Mass same, volume half: density double. 1.2 × 2 = 2.4 kg per cubic metre.
Q3. Pot ko neeche se heat karne pe water upar-neeche ghoomta hai (convection). Kyun?
(a) Neeche ka hot water kam density ka hoke upar aata hai; upar ka cold water neeche jaata hai
✅ Sahi! Heat se volume badha, density ghati: hot water upar. Cold water ki density zyada: neeche.
(b) Hot water ki density badh jaati hai, isliye neeche jaata hai
❌ Galat: Rule reverse lagaya. Heat se volume badhta hai, density ghatti hai.
(c) Hot water ka mass kam ho jaata hai
❌ Galat: Heat se mass kam maana. Mass same rehta hai; volume badhta hai.
(d) Cold water ka volume badh jaata hai
❌ Galat: Cooling ko expansion maana. Cool karne pe volume ghatta hai (contraction).
Q4. Heat karne pe kaun sabse zyada expand karta hai, kaun sabse kam?
(a) Solid sabse zyada, phir liquid, gas sabse kam
❌ Galat: Order reverse kar diya. Gas sabse zyada failti hai.
(b) Gas sabse zyada, phir liquid, solid sabse kam
✅ Sahi! Gas ke particles pehle se door-door: sabse zyada failti hai. Liquid usse kam, solid sabse kam.
(c) Liquid sabse zyada, phir gas, solid sabse kam
❌ Galat: Gas aur liquid ki jagah badal di. Gas liquid se zyada failti hai.
(d) Teeno equal expand karte hain
❌ Galat: Sab ko equal maana. Expansion: gas, phir liquid, phir solid.
Q5. Hot air balloon upar kyun uthta hai?
(a) Hot air ka mass zyada hota hai
❌ Galat: Heat se mass badha maana. Mass same, volume zyada: density kam.
(b) Hot air ki density zyada hoti hai
❌ Galat: Rule reverse lagaya. Heat se density ghatti hai.
(c) Andar ki hot air ki density bahar ki cold air se kam hai
✅ Sahi! Heat se air expand hui, density ghati. Kam density wali cheez upar aati hai.
(d) Balloon ka cloth light hai, density se koi lena-dena nahi
❌ Galat: Density ko ignore kiya. Hot air ki kam density hi balloon ko upar le jaati hai.
📚 Aur Padho (External Reference)
- NCERT Class 8 Science Curiosity, Chapter 9 (official PDF)
- DIKSHA: Sarkar ka free learning platform, NCERT ke videos ke liye
💖 CharuMam Motivation
Aaj humne dekha ki ek hi cheez garmi mein fail jaati hai aur thand mein sikud jaati hai. Halaat badalte hain, toh padarth bhi apna roop badal leta hai, par uske kan, uska “mass”, wahi rehta hai.
Beta, zindagi mein bhi kabhi garmi aayegi, kabhi thand: kabhi number achhe aayenge, kabhi kam. Halaat ke saath thoda dhalna theek hai, par apni asli cheezein mat chhodna: mehnat, imaandaari aur seekhne ki lagan. Aur paani ki tarah kabhi-kabhi sabse alag chalna bhi theek hai; usi “ulte” vyavhaar se toh jheel ki machhliyaan bachti hain! 🐟✨
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