Resistance Kis Par Nirbhar Karta Hai - Class 10 Science

Char Cheezein 🔍

Pichhle lesson mein humne dekha ki resistance electrons ke takraane se aata hai. Toh takkarein kis-kis cheez se badhti hain?

📌 Kisi taar ka resistance chaar cheezon par nirbhar karta hai:
1️⃣ Lambai (L) — jitna lamba, utna zyada resistance (R ∝ L)
2️⃣ Motai / area (A) — jitna mota, utna kam resistance (R ∝ 1/A)
3️⃣ Metal (material) — har metal (dhaatu) ka apna swabhaav
4️⃣ Taapmaan — garam taar ki resistance zyada

Pehli teen ko milakar:
R = ρ L / A

Yahan ρ (rho) = resistivity, us metal ka apna gun. Ikai: ohm-metre (Ω m)

Lambai badhao toh resistance badhta hai; motai badhao toh ghatta hai. Par dhyaan do — motai dugni karne par resistance CHAUTHAI ho jaata hai, aadha nahi.

📊 Resistivity — Har Metal Ka Apna Number

Resistivity (ρ) sirf metal par nirbhar karta hai — taar ki lambai ya motai par bilkul nahi. Ye us metal ki apni pehchaan hai, jaise density.

Metal	ρ (Ω m)	Kahan use hota hai
Silver (chaandi)	1.6 × 10⁻⁸	Sabse achha conductor, par mehnga
Copper	1.6 × 10⁻⁸	Ghar ki wiring, motor
Aluminium	2.7 × 10⁻⁸	Bijli ke lambe taar (halka hai)
Tungsten	5.2 × 10⁻⁸	Bulb ka filament
Manganin	44 × 10⁻⁸	Standard resistor
Nichrome	100 × 10⁻⁸	Heater, iron, toaster, geyser
Rubber / plastic	10¹³ – 10¹⁷	Insulation (taar ka cover)

🎯 Do bade sawaal, ek hi table se hal:

❓ Taar copper ka kyun hota hai? Kyunki copper ki resistivity bahut kam hai (1.6 × 10⁻⁸) — yani current bina zyada garmi ke bah jaata hai, aur energy bekaar nahi jaati.

❓ Heater ka coil nichrome ka kyun hota hai? Do wajah:
🔹 Uski resistivity copper se lagbhag 62 guna zyada hai → bahut zyada garmi paida karta hai (yahi toh chahiye!)
🔹 Aur wo bahut garam hone par bhi oxidise (jalta) nahi — isliye saalon chalta hai

❓ Bulb ka filament tungsten ka kyun? Kyunki tungsten ka melting point 3380 °C hai — sabse zyada. Wo safed garam hokar chamak sakta hai bina pighle.

❄️ Superconductor — resistance BILKUL zero

Kuch metals jab bahut thandi ki jaati hain (lagbhag −269 °C tak), toh unki resistance bilkul zero ho jaati hai! Ise superconductivity kehte hain.

Iska matlab: usme current bina kisi energy ke nuksaan ke, hamesha ke liye bah sakta hai. Ek baar chalu karo toh saalon chalta rahega.

Aaj iska istemaal MRI machine mein hota hai (aspatal mein jo badi machine sar ka scan karti hai), aur bade particle accelerator mein.

Sapna kya hai? Ek aisa superconductor jo saamanya taapmaan par kaam kare. Agar wo mil gaya toh bijli ki lines mein hone wala poora nuksaan khatam ho jaayega — aur bharat jaise desh mein jahan lagbhag 20% bijli raaste mein hi zaya ho jaati hai, ye ek kranti hogi.

🧮 Hal Kiye Hue Sawaal

📝 Sawaal 1 — Taar Ka Resistance

Ek copper ka taar 1 m lamba hai aur uska vyaas (diameter) 0.5 mm hai. Uska resistance nikaalo. (ρ_copper = 1.6 × 10⁻⁸ Ω m)

Step 1 — area nikaalo (yaad rakho: diameter di hai, radius chahiye!)
r = 0.5/2 = 0.25 mm = 0.25 × 10⁻³ m
A = πr² = 3.14 × (0.25 × 10⁻³)² = 3.14 × 6.25 × 10⁻⁸ = 1.963 × 10⁻⁷ m²

Step 2 — formula: R = ρL/A
R = (1.6 × 10⁻⁸ × 1) / (1.963 × 10⁻⁷)
R = 0.0815 Ω

✅ Bahut kam! Isiliye ghar ki wiring mein taar ki apni resistance ko lagbhag nazarandaz kar diya jaata hai.

📝 Sawaal 2 — Ab Lambai Dugni Karo

Usi taar ko 2 m lamba kar diya jaaye toh resistance?

Hal: R ∝ L, aur lambai dugni ho gayi
R = 2 × 0.0815 = 0.163 Ω — bilkul dugna.

📝 Sawaal 3 — Ab Motai Dugni Karo (Board Favourite)

Usi 1 m taar ka vyaas 0.5 mm se 1 mm kar diya jaaye toh resistance?

Soch: vyaas dugna → radius dugna → area 4 guna (kyunki A = πr²) → resistance chauthai

Hal: R = 0.0815 / 4 = 0.0204 Ω

⚠️ Sabse aam galti: log sochte hain motai dugni = resistance aadha. Nahi! Resistance area par nirbhar karta hai, motai par nahi — aur area vyaas ke varg ke ratio (anupaat) mein hota hai.

📝 Sawaal 4 — Nichrome Vs Copper

Ek nichrome taar aur ek copper taar, dono 1 m lambe aur dono ka area 10⁻⁶ m². Dono ka resistance nikaalo.

Nichrome: R = (100 × 10⁻⁸ × 1) / 10⁻⁶ = 1 Ω
Copper: R = (1.6 × 10⁻⁸ × 1) / 10⁻⁶ = 0.016 Ω

✅ Nichrome ka resistance copper se lagbhag 62 guna zyada — bilkul waisa hi jaisa heater ke liye chahiye.

📝 Practice — Khud Karo

Ek taar ka resistance 10 Ω hai. Agar use kheench kar dugna lamba kar diya jaaye (metal utni hi rahegi, isliye area aadha ho jaayega), toh naya resistance?

Jawab: R = ρL/A. Lambai 2 guna aur area 1/2 guna → R 4 guna ho jaayega.
Naya R = 4 × 10 = 40 Ω

💡 Ye sawaal exam mein bahut aata hai. Kheenchne par metal ki maatra nahi badalti — isliye lambai badhne par area utna hi ghatna chahiye.

🇮🇳 India Connection

Bharat mein bijli ka ek bada hissa ghar tak pahunchne se pehle hi raaste mein zaya ho jaata hai — ise transmission loss kehte hain. Kai rajyon mein ye 15-20% tak raha hai, jo duniya mein kaafi zyada hai (kai deshon mein ye 5-7% hai).

Iska ek bada kaaran wahi hai jo aap abhi padh rahe ho: H = I²Rt. Purane, patle aur zyada resistance wale taar bijli ko garmi mein badal dete hain — aur wo garmi hawa mein chali jaati hai.

Ilaaj? Mote taar (kam R), aur bijli ko bahut zyada voltage par bhejna (kyunki utni hi power ke liye kam current chahiye, aur I² mein kami ka asar bahut bada hota hai). Isiliye aapne khambon par "33,000 volt — Khatra" jaise board dekhe honge.

Ek chhota sa formula, aur usse desh ke hazaron crore rupaye ki bachat.

🧠 Apne Aap Ko Test Karo

Q1. Taar ka resistance ka formula kya hai?

Q2. Taar ki lambai dugni kar dein (motai wahi) toh resistance?

Q3. Taar ka VYAAS dugna kar dein toh resistance?

Q4. Heater ka coil nichrome ka kyun hota hai?

Q5. Resistivity kis par nirbhar karti hai?

Q6. Ek 10 Ω ka taar kheench kar dugna lamba kar diya. Naya resistance?

🔬 Resistance Explorer mein lambai, motai aur metal badal kar electrons ko takraate dekho!

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