⚛️ भौतिक विज्ञान (Physics)

📌 0. Exam Pattern & 2025 Analysis (2 min read)

• Science ke 10 sawal: Physics 4 + Chemistry 3 + Biology 3. Physics = har shift mein 4 sawal (Science mein sabse zyada).
• Official 2025 paper (16–21 Jan 2026, 12 shifts, 48 Physics sawal) ka topic-wise hisaab:
  • Magnetism & EMI — 11 sawal (Fleming rule, F = BIL, flux, Lenz, solenoid) — sabse important!
  • Electricity/Electrostatics/Semiconductor — 7 | Light (mirror/lens) — 6 | Heat & Kinetic theory — 5
  • Units — 4 | Force/Rotation (moment of inertia) — 4 | Work-Energy — 3 | Gravitation, Pressure, Sound — 2-2 | Motion, Nuclear — 1-1.
• ⚠️ Kai sawal NCERT class 11-12 level ke the (moment of inertia, kinetic theory, point dipole, band theory). Chhote numericals (P = 1/f, R = 2f, parallel resistance, F = BIL) bhi aaye — formula yaad rakho.

📌 1. मात्रक एवं मापन (Units & Measurement) (7 min read)

1.1 मूल राशियाँ व 7 SI मात्रक (Fundamental Quantities)

Base (मूल) quantities kisi doosri quantity par nirbhar nahi hotin. SI (International System, 1960) mein 7 base units hain:

Supplementary: समतल कोण — radian (rad); ठोस कोण — steradian (sr).

1.2 व्युत्पन्न मात्रक (Derived Units)

Base units ko guna/bhaag karke banne wali quantities = व्युत्पन्न (derived) — velocity (m/s), acceleration (m/s²), force, area, volume, density.

1.3 महत्वपूर्ण रूपांतरण (Must-know Conversions)

1.4 अदिश व सदिश (Scalar & Vector)

• अदिश (Scalar) — sirf parimaan: doori, chaal (speed), mass, samay, kaarya, urja, shakti, taap, daab (pressure), vidyut dhara (current).
• सदिश (Vector) — parimaan + disha: vishthapan, veg (velocity), tvaran, bal, bhaar (weight), sanveg, vidyut kshetra, chumbakiya kshetra.
• ⚠️ Current ki disha hoti hai, phir bhi scalar hai (kyunki vector jod ke niyam nahi maanta).

📌 2. गति (Motion) (5 min read)

2.1 मूल अवधारणाएँ (Basic Concepts)

• दूरी (Distance) — kul tay raasta (scalar). विस्थापन (Displacement) — shuruaati aur antim bindu ke beech ki seedhi doori, disha sahit (vector). Displacement ≤ distance; ek poora gol chakkar lagane par displacement = 0.
• चाल (Speed) = distance/time; वेग (Velocity) = displacement/time. त्वरण (Acceleration) = velocity mein badlav/time (m/s²). Ghat-ta hua veg = मंदन (retardation).
• Average speed (do barabar doori v₁ aur v₂ se) = 2v₁v₂/(v₁ + v₂) — seedha ausat nahi!
• एकसमान वृत्तीय गति (Uniform circular motion): speed same, par disha lagataar badalti hai → velocity badalti hai → ye त्वरित गति (accelerated motion) hai. Disha har bindu par sparsh rekha (tangent) ki taraf.

2.2 गति के समीकरण (Equations of Motion — uniform acceleration)

v = u + at  |  s = ut + ½at²  |  v² = u² + 2as  (u = shuruaati veg, v = antim veg, a = tvaran, s = displacement)

• मुक्त पतन (Free fall): a = g ≈ 9.8 m/s². Nirvaat (vacuum) mein bhaari aur halki cheezein (pankh aur sikka) ek saath girti hain (Galileo). Hawa mein pankh dheere — hawa ka pratirodh.
• प्रक्षेप्य (Projectile): 45° par phenkne se maximum range.

2.3 ग्राफ (Graphs — sawal zaroor aata hai)

• x-t graph time axis ke parallel → vastu ruki hui; v-t graph time axis ke parallel → ekasman veg (a = 0).

📌 3. बल, न्यूटन के नियम व घूर्णन (Force, Newton's Laws & Rotation) (8 min read)

3.1 न्यूटन के गति के 3 नियम (Newton's Laws)

• प्रथम नियम — जड़त्व का नियम (Law of Inertia): vastu ruki hai to ruki rahegi, chal rahi hai to seedhi ek-saman veg se chalti rahegi, jab tak bahari asantulit bal na lage. Isse bal ki paribhasha milti hai. Jadatva mass par nirbhar — bhaari vastu ka jadatva zyada.
  • Chalti bus mein achanak brake → yatri aage jhukte hain (gati ka jadatva).
  • Ruki bus achanak chale → yatri peeche girte hain (vishram ka jadatva).
  • Kambal ko dande se peetne par dhool alag; ped hilane par phal girna; carrom ki goti neeche se maarne par upar wali wahi rehti hai.
• द्वितीय नियम — F = ma: sanveg badalne ki dar lagaaye gaye bal ke baraabar: F = Δp/Δt. Isse bal ka sutra/maap milta hai. Unit newton.
  • Cricketer catch lete samay haath peeche kheenchta hai → samay (Δt) badhta hai → bal kam → chot nahi. Isi tarah high-jump mein gadde/ret, gaadi mein airbag, shock absorber.
• तृतीय नियम — क्रिया-प्रतिक्रिया (Action-Reaction): har kriya ki barabar aur vipreet pratikriya; dono alag-alag vastuon par lagti hain (isliye cancel nahi hotin).
  • Rocket (gas neeche → rocket upar), bandook ka peeche dhakka (recoil), naav se kinaare kudne par naav peeche, tairna, chalna (zameen ko peeche dhakelte hain).

3.2 संवेग व संवेग संरक्षण (Momentum)

• संवेग (Momentum) p = mv (kg·m/s, vector). आवेग (Impulse) = F × Δt = Δp.
• रेखीय संवेग संरक्षण: bahari bal na ho to system ka kul sanveg constant. Rocket propulsion, bandook ka recoil, visphot — isi par (aur 3rd law par).

3.3 घर्षण व वृत्तीय गति (Friction & Circular Motion)

• घर्षण (Friction): sthaitik (static) > sarpi (sliding/kinetic) > lotanik (rolling) — sabse kam. Isliye pahiye aur ball-bearing. Kam karna: lubricant (tel/grease), ball bearing, chikni satah. Badhana: tyre ke khaanche (treads), jooton ke sole. Ghashan ke bina chalna sambhav nahi.
• अभिकेंद्रीय बल (Centripetal force) — vritt ke kendra ki taraf; vritiya gati ke liye zaroori (jaise pathar ko rassi se ghumana). Apkendriya (centrifugal) — kaalpanik (pseudo) bal: washing machine drier, cream separator.
• Mod par sadak ka bahari kinara unchaa = banking of roads; cyclist mod par andar jhukta hai.

3.4 Advanced (11): घूर्णन गति व जड़त्व आघूर्ण (Rotation & Moment of Inertia)

• बल आघूर्ण (Torque) = bal × dhure se lambvat doori. Darwaze ka handle kabze se door lagate hain → kam bal mein zyada torque. Paana (spanner) lamba = aasaan.
• जड़त्व आघूर्ण (Moment of Inertia, I) = ghoomne mein jadatva. Ye mass aur mass ke dhure (axis) se vitaran par nirbhar — mass jitna door, I utna zyada.

• Aanat tal (inclined plane) par lotne ki race: jiska I/MR² kam, wo pehle pahunchta hai (mass/radius se farq nahi): thos gola > thos belan/disc > khokhla gola > ring/khokhla belan.
• कोणीय संवेग संरक्षण: ice skater/gotakhor haath sikodta hai → I kam → tezi se ghoomta hai.
• गुरुत्व केंद्र (Centre of gravity) neeche → zyada sthirta (bus mein samaan neeche, kursi ka chauda aadhar).

📌 4. गुरुत्वाकर्षण (Gravitation) (6 min read)

• न्यूटन का सार्वत्रिक गुरुत्वाकर्षण नियम: F = G m₁m₂ / r² — bal masses ke gunanfal ke samanupati aur doori ke varg ke vyutkramanupati (inverse-square law). G = 6.67 × 10⁻¹¹ N·m²/kg² — sarvatrik niyatank (har jagah same).
• Gurutviya tvaran g = GM/R² ≈ 9.8 m/s². g vastu ke mass par nirbhar nahi.
  • Dhruvon (poles) par sabse zyada, bhoomadhya rekha (equator) par sabse kam (Prithvi dhruvon par chapti + ghoornan).
  • Unchai par jaane par ghat-ta hai; gehraai mein jaane par bhi ghat-ta hai; Prithvi ke kendra par g = 0.
  • Agar Prithvi ghoomna band kar de to equator par g badh jaayega.
• द्रव्यमान (Mass) — padarth ki matra, har jagah same, kg, beam balance (tarazu). भार (Weight) = mg, bal hai, newton, spring balance. Chandrama par g ≈ Prithvi ka 1/6 → bhaar 1/6, mass same.
• Lift mein bhaar: upar tvarit → zyada; neeche tvarit → kam; mukt pataan (rassi toot jaaye) → shunya (भारहीनता / weightlessness). Antariksh yaan mein yatri isi kaaran bhaarheen mehsoos karte hain.
• Chandrama ka tvaran: Chandrama Prithvi ke kendra se ~60 R door hai → uska tvaran g/60² = g/3600 — inverse-square law ki pushti (Newton).
• Jwaar-bhaata (Tides) — mukhyatah Chandrama (aur Surya) ke gurutvakarshan se.
• केप्लर के नियम: (1) grah Surya ke chaaron ore deerghvrittiya (elliptical) kaksha mein, Surya ek focus par; (2) grah aur Surya ko jodne wali rekha samaan samay mein samaan kshetrafal (areal velocity constant) — Surya ke paas grah tez; (3) T² ∝ r³.
• पलायन वेग (Escape velocity): Prithvi — 11.2 km/s; Chandrama — ~2.4 km/s (isliye Chandrama par vayumandal nahi). Kakshiya veg (Prithvi ke paas) ≈ 7.9 km/s.
• भूस्थिर उपग्रह (Geostationary satellite): equator ke upar ~36,000 km (35,786 km) unchai, aavartkaal 24 ghante, pashchim se poorv ghoomta hai — Prithvi se ruka hua dikhta hai (TV, sanchar, mausam).
• Upagrah ki urja: vritiya kaksha mein gurutvakarshan bal veg ke lambvat → gurutv dwara kaarya shunya; PE + KE = constant (urja sanrakshan).

📌 5. कार्य, ऊर्जा एवं शक्ति (Work, Energy & Power) (6 min read)

5.1 कार्य (Work)

• W = F × s × cos θ (θ = bal aur vishthapan ke beech kon). Unit: joule. Kaarya tabhi jab bal lage aur vishthapan ho.
• Shunya kaarya (θ = 90°): coolie sir par bojh lekar kshaitij (horizontal) platform par chale → gurutv ke viruddh kaarya = 0; vritiya kaksha mein upagrah par gurutv ka kaarya = 0; deewar ko dhakelna (vishthapan 0) → kaarya 0.
• Rinaatmak (negative) kaarya: ghashan bal (gati ke vipreet); upar phenki gend par gurutv.
• Gurutv ke viruddh uthane mein kaarya = mgh → sirf mass aur unchai par nirbhar; samay ya raaste par nahi.

5.2 ऊर्जा (Energy)

• गतिज ऊर्जा (Kinetic) KE = ½ mv² — chalti gaadi, goli, behta paani. Veg 2 guna → KE 4 guna; 3 guna → 9 guna. KE = p²/2m (p = sanveg).
• स्थितिज ऊर्जा (Potential) PE = mgh — sthiti ya aakaar ke kaaran: baandh ka paani, kheencha dhanush, ghadi ki chaabi (spring).
• ऊर्जा संरक्षण (Conservation): urja na banti hai, na nasht hoti hai — sirf roop badalti hai. Upar phenki gend: upar jaate KE → PE, neeche aate PE → KE; kul yantrik urja har bindu par constant (hawa ka pratirodh na ho to). Pendulum bhi.
• Chalti car achanak rokne par KE ooshma (brake/tyre garam) aur dhwani mein badal jaati hai — gaayab nahi hoti.

5.3 शक्ति (Power)

• P = W / t (kaarya karne ki dar); unit watt (W) = J/s. 1 kW = 1000 W; 1 HP = 746 W.
• Ghar ka bijli bill kWh ("unit") mein — ye urja ki unit hai: 1 kWh = 3.6 × 10⁶ J. Jaise 100 W ka bulb 10 ghante = 1 kWh = 1 unit.

📌 6. दाब, उत्प्लावन व तरल (Pressure, Buoyancy & Fluids) (7 min read)

6.1 दाब (Pressure)

• दाब = बल / क्षेत्रफल (P = F/A), unit pascal (N/m²), scalar. Kam kshetrafal → zyada daab: tez chaaku, nukeeli keel, injection ki sui. Zyada kshetrafal → kam daab: school bag ke chaude patte, truck ke chaude tyre, oont ke chaude pair, reti mein chalna.
• द्रव का दाब = hρg — gehraai ke saath badhta hai → baandh (dam) ki deewar neeche moti; gotakhor ko special suit.
• वायुमंडलीय दाब: 1 atm ≈ 1.013 × 10⁵ Pa ≈ 76 cm Hg. Barometer (Torricelli) se naapte hain. Unchai par ghat-ta hai → pahad par naak se khoon, hawai jahaz mein fountain pen se syahi nikalna. Barometer ka paara achanak girna → toofan/aandhi.
• पास्कल का नियम: band drav par lagaya daab har disha mein barabar failta hai → hydraulic lift, hydraulic brake, hydraulic press.

6.2 उत्प्लावन व आर्किमिडीज़ सिद्धांत (Buoyancy & Archimedes)

• उत्प्लावन बल (Buoyant force) — drav dwara upar ki taraf lagaya bal. Archimedes: ye bal = vastu dwara hataaye gaye drav ka bhaar = ρ_drav × V_{dooba hua} × g. Isliye ye vastu ke mass par nahi, hataaye gaye drav ke aayatan aur ghanatva par nirbhar.
• Drav mein vastu ka "aabhasi bhaar kam hona" (apparent loss of weight) = upar ki taraf utplavan bal.
• Tairne ka niyam: vastu ka ghanatva < drav ka → tairti hai; zyada → doobti hai. Jahaz (lohe ka) khokhla hone se zyada paani hataata hai → tairta hai; lohe ki keel doobti hai.
• Barf (ghanatva ~0.92 g/cm³) paani par tairti hai, lagbhag 9/10 hissa dooba. Samudri paani zyada ghana → usme tairna aasaan. Paani ka ghanatva 4°C par sabse zyada.
• आपेक्षिक घनत्व (Relative density) = padarth ka ghanatva / paani ka ghanatva (koi unit nahi) — hydrometer se; doodh ke liye lactometer.

6.3 बर्नौली, पृष्ठ तनाव, केशिकत्व, श्यानता

• बर्नौली सिद्धांत: jahan drav/hawa ki chaal zyada, wahan daab kam → hawai jahaz ko lift, aandhi mein chhat ud jaana, tez train ke paas khade hone par kheencha jaana, sprayer/atomizer.
• पृष्ठ तनाव (Surface tension): drav ki satah khinchi jhilli jaisi → boondein gol, keede paani par chalte hain, sui paani par tair sakti hai. Sabun/detergent aur garmi surface tension kam karte hain (garam sabun paani achha saaf karta hai).
• केशिकत्व (Capillarity): patli nali mein drav ka chadhna — laalten/diye ki batti mein tel, blotting paper, towel paani sokhta hai. Paara (mercury) nali mein neeche utarta hai.
• श्यानता (Viscosity): drav ka "gaadhapan" (shahad > paani). Garmi se drav ki viscosity ghat-ti, gas ki badhti hai.

📌 7. ऊष्मा व ताप (Heat & Temperature) (8 min read)

7.1 ताप व पैमाने (Temperature Scales)

• ऊष्मा (Heat) = urja ka roop (joule/calorie) jo garam se thandi vastu ki taraf behti hai. ताप (Temperature) = garmi ki degree (kelvin). Thermometer se.
• Rupantaran sutra: C/5 = (F − 32)/9 = (K − 273)/5 (sahi maan: K = C + 273.15).

• Clinical thermometer: 35°C–42°C (kink hota hai — paara wapas nahi girta). Lab thermometer: −10°C–110°C. Paara (mercury) −39°C par jam jaata hai → bahut thand ke liye alcohol thermometer. Bahut ucch taap (bhatti, Surya) → pyrometer.

7.2 विशिष्ट ऊष्मा व गुप्त ऊष्मा (Specific & Latent Heat)

• Q = m c ΔT. Paani ki vishisht ooshma sabse zyada (~4186 J/kg·K, 1 cal/g·°C) → garmi der tak rakhta hai: car radiator coolant, garam paani ki bottle (sekai), samudri kinaare ka mausam sam (moderate).
• गुप्त ऊष्मा (Latent heat): avastha badalte samay taap badle bina sokhi/chhodi garmi. Barf pighalne ki (fusion) ≈ 3.34 × 10⁵ J/kg (80 cal/g); paani ubalne ki (vaporisation) ≈ 22.5 × 10⁵ J/kg (~540 cal/g).
  • Vaporisation ki latent heat, fusion se zyada kyunki gas banane mein anuon ko poori tarah alag karna padta hai (intermolecular bal poori tarah todna).
  • 100°C ki bhaap (steam) ka jalna 100°C ke paani se zyada khatarnaak — extra latent heat.
  • 0°C ki barf, 0°C ke paani se zyada thanda karti hai.
• वाष्पन से ठंडक: matka, paseena, cooler.

7.3 ऊष्मा संचरण (Heat Transfer)

• Kaali/khurdari satah achha avshoshak aur utsarjak (radiator); safed/chamkeeli kam. Garmi mein safed, sardi mein gehre rang ke kapde.
• Thermos flask (Dewar) — do deewaron ke beech nirvaat (conduction+convection rukta hai) + chamkeeli satah (radiation rukta hai).
• Stefan ka niyam (12): vastu dwara vikirit urja E ∝ T⁴ (T kelvin mein). T double → E 16 guna.
• Taapiya pratirodh (Thermal resistance) R = L / (kA) — motaai (L) ke samanupati, kshetrafal aur chalakta (k) ke vyutkramanupati.
• Taapiya prasaar (Expansion): rail ki patriyon ke beech jagah, bijli ke taar garmi mein dheele. Paani ka asaamanya prasaar — 0°C se 4°C garam karne par sikudta hai; 4°C par ghanatva max → jheel upar se jamti hai, neeche machhliyan zinda.

7.4 Advanced (11): अणुगति सिद्धांत (Kinetic Theory of Gases)

• Gas ke anuon ki ausat gatij urja = (3/2) kT → sirf absolute temperature (K) ke samanupati. T aadha → KE aadhi.
• Chaal: v_rms = √(3kT/m) > v_avg = √(8kT/πm) > v_p (most probable) = √(2kT/m).

📌 8. ध्वनि (Sound) (6 min read)

8.1 ध्वनि की प्रकृति (Nature)

• Dhwani = yantrik (mechanical) tarang — chalne ke liye madhyam chahiye; nirvaat (vacuum) mein nahi chalti (antariksh mein astronauts radio se baat karte hain). Hawa mein ye अनुदैर्ध्य (longitudinal) tarang hai — kan aage-peeche kampan karte hain.
• संपीडन (Compression) = kan paas-paas, ucch daab / ucch ghanatva. विरलन (Rarefaction) = kan door-door, kam daab / kam ghanatva.
• v = f × λ (chaal = aavritti × tarang-dairghya).

8.2 ध्वनि की चाल (Speed of Sound)

• Chaal madhyam ke gunon (pratyasthata/elasticity aur ghanatva) aur taap par nirbhar; amplitude ya aavritti par nahi.
• Thos > Drav > Gas. NCERT (25°C): steel ~5960 m/s, aluminium ~6420 m/s, paani (distilled) ~1498 m/s, hawa ~346 m/s. Hawa mein 0°C par 331 m/s, 22°C par 344 m/s.
• Taap badhne par chaal badhti hai; nami (humidity) badhne par bhi badhti hai.
• Bijli ki chamak pehle, garaj baad mein — prakash (3 × 10⁸ m/s) dhwani se bahut tez.

8.3 ध्वनि के गुण (Characteristics)

8.4 परावर्तन, प्रतिध्वनि व अन्य (Reflection, Echo etc.)

• प्रतिध्वनि (Echo): kaan mein dhwani ka asar ~0.1 s rehta hai → spasht echo ke liye deewar kam se kam 17.2 m door (344 m/s × 0.1 s ÷ 2).
• अनुरणन (Reverberation): baar-baar paravartan se awaaz gunjna — auditorium mein dhwani-sokhne wali saamagri (parde, fibre board).
• Stethoscope, megaphone, sound board — dhwani ke bahu-paravartan par.
• SONAR (Sound Navigation And Ranging) — ultrasonic tarangon se samudra ki gehraai, pandubbi (submarine). RADAR — radio tarangen (dhwani nahi).
• डॉप्लर प्रभाव: paas aate srot ki awaaz ka pitch badhta, door jaate ka ghat-ta (train ki seeti; police speed gun).
• Supersonic — dhwani se tez; sonic boom. Mach number = vastu ki chaal / dhwani ki chaal.
• अनुनाद (Resonance): sainik pul par kadam milaakar nahi chalte (pul ki natural frequency se mel kha kar tootne ka khatra).

📌 9. प्रकाश (Light) — दर्पण, लेंस, नेत्र, परिघटनाएँ (12 min read)

9.1 मूल बातें

• Prakash = vidyut-chumbakiya (electromagnetic) tarang — madhyam ki zaroorat nahi. Nirvaat mein chaal c = 3 × 10⁸ m/s (sabse tez). Surya se prithvi tak ~8 min 20 s.
• Prakash seedhi rekha mein chalta hai → chhaaya (shadow), grahan, pinhole camera (ulta pratibimb).

9.2 परावर्तन व दर्पण (Reflection & Mirrors)

• Niyam: aapatan kon = paravartan kon; aapatit kiran, paravartit kiran aur abhilamb ek hi tal mein.
• Samtal darpan (Plane mirror): pratibimb aabhasi, seedha, same size, darpan ke peechhe utni hi doori par, paarshvik ulta (lateral inversion) — isliye ambulance ke aage "AMBULANCE" ulta (mirror image mein) likha hota hai, taaki aage wali gaadi ke rear-view mirror mein seedha padha jaaye. Poora pratibimb dekhne ke liye darpan ki unchai = vyakti ki aadhi.
• Do samtal darpan θ kon par: pratibimb n = 360/θ − 1 (jab 360/θ sam ho). 90° → 3; 60° → 5; samaantar → anant (kaleidoscope mein bahu-paravartan).
• Goliya darpan: R = 2f. Samaantar kiranen avtal (concave) darpan se paravartan ke baad focus (F) par milti hain. Darpan sutra: 1/v + 1/u = 1/f.

9.3 अपवर्तन (Refraction)

• Prakash ek madhyam se doosre mein jaate hue chaal badalne se mudta hai. Apvartanank n = c / v. Virl (rarer) → saghan (denser): abhilamb ki ore mudta hai.
• Udaharan: paani mein pencil tuti dikhna, taalab kam gehra dikhna, taaron ka timtimana (vaayumandaliya apvartan), Surya ~2 minute pehle dikhna aur ~2 minute baad tak dikhna.

• Prakashiya saghanta ≠ dravyaman ghanatva: kerosene paani se halka hai par prakashiya roop se saghan (1.44 > 1.33).
• पूर्ण आंतरिक परावर्तन (TIR): saghan → virl mein, kon > krantik kon (critical angle). Heere ki chamak (krantik kon ~24°), optical fibre, marichika (mirage).

9.4 लेंस (Lenses)

• Uttal (Convex) lens = abhisaari (converging): samaantar kiranen focus se guzarti hain. Avtal (Concave) lens = apsaari (diverging).
• Lens sutra: 1/v − 1/u = 1/f. Kshamata (Power) P = 1/f (f metre mein), unit dioptre (D). Convex +, concave −. Jaise +5 D → f = 1/5 = 0.2 m (20 cm); −2 D → concave, f = −50 cm.
• Uttal lens: vastu 2F par → pratibimb 2F par (same size); F aur 2F ke beech → 2F se pare, bada, vaastavik ulta; F aur lens ke beech → aabhasi, seedha, bada (aavardhak lens / magnifying glass).
• Avtal lens: vaastavik vastu ka pratibimb hamesha aabhasi, seedha, chhota. Isliye bada vaastavik pratibimb sirf convex lens (ya concave mirror) de sakta hai.

9.5 मानव नेत्र व दृष्टि दोष (Human Eye & Defects)

• Cornea (sabse zyada apvartan), Iris (aankh ka rang; pupil ka size niyantrit), Pupil, Lens (uttal; ciliary muscles focal length badalti hain = समंजन क्षमता / accommodation), Retina (parda; pratibimb vaastavik aur ulta). Rods = mand prakash, Cones = rang. Optic nerve jahan nikalti hai = andh bindu (blind spot).
• Swasth aankh: nikat bindu 25 cm, door bindu anant. Drishti-sthirta ~1/16 s (cinema isi par).

9.6 वर्ण-विक्षेपण व प्रकीर्णन (Dispersion & Scattering)

• Prism se safed prakash 7 rangon mein — VIBGYOR (बैं नी आ ह पी ना ला). Baingani (violet) sabse zyada mudta, laal sabse kam. Newton ne dikhaaya.
• Indradhanush: paani ki boondon mein apvartan + vikshepan + aantarik paravartan; hamesha Surya ke vipreet disha mein dikhta hai.
• Prakeernan (Scattering, Rayleigh): chhoti tarang-dairghya (neela) zyada bikharta hai → aasmaan neela. Suryoday/suryast par Surya laal. Khatre ke signal laal (sabse kam bikharta, door tak dikhta). Antariksh yatri ko aasmaan kaala. Baadal safed (bade kan sab rang bikherte). Tyndall effect — colloid mein prakash ka raasta dikhna.
• Raman prabhav (1928) — C.V. Raman, Nobel 1930; 28 Feb = Rashtriya Vigyan Diwas.

📌 10. विद्युत (Electricity) (10 min read)

10.1 आवेश व धारा (Charge & Current)

• Aavesh (charge) ki unit coulomb; ek electron ka aavesh e = 1.6 × 10⁻¹⁹ C. Samaan aavesh pratikarshan, vipreet aakarshan.
• Coulomb ka niyam: F ∝ q₁q₂/r² (vyutkram varg).
• Vidyut dhara I = Q/t, unit ampere. Paramparik dhara ki disha electron ke pravah ke vipreet. Ammeter series mein, voltmeter parallel mein.
• Vibhavaantar (Potential difference) V = W/Q, unit volt.
• Anant samtal chaadar (plane sheet) ke paas kshetra E = σ/2ε₀ → prishth aavesh ghanatva σ ke samanupati.
• Vidyut dwidhruv (dipole): p = q × 2a. "Bindu dwidhruv" = q → ∞ aur 2a → 0 jabki p seemit rahe.

10.2 ओम का नियम व प्रतिरोध (Ohm's Law & Resistance)

• V = IR (niyat taap par). V–I graph = moolbindu se guzarti seedhi rekha. Unit ohm (Ω).
• Non-ohmic (niyam nahi maante): diode, transistor, electrolyte. Dhatu ke taar (copper, nichrome) ohmic hain.
• R = ρL/A — lambaai ke samanupati, kshetrafal ke vyutkramanupati; ρ = pratirodhakta (padarth aur taap par nirbhar). Dhatu ka pratirodh taap badhne par badhta hai.
• Taar ko khinchkar lambaai n guna (aayatan same) → A 1/n → R = n² guna. Double → 4 guna.
• Sabse achha chaalak chaandi (silver), phir tamba (copper), sona, aluminium. Bijli ke taar copper/aluminium ke.
• Nichrome (Ni-Cr-Fe mishradhatu) — ucch pratirodhakta, ucch galnaank → heater, press, geyser ka element. Bulb ka filament = tungsten (galnaank ~3422°C); bulb mein nishkriya gas (argon/nitrogen).
• Fuse: kam galnaank ka taar (tin-lead mishradhatu), circuit mein series mein; zyada dhara par pighal kar circuit tod deta hai. Aajkal MCB.

Example: 3 Ω ‖ 6 Ω → R = (3×6)/(3+6) = 18/9 = 2 Ω.

10.3 शक्ति व घरेलू विद्युत (Power & Domestic)

• P = VI = I²R = V²/R. Joule ka ooshma niyam H = I²Rt → heater, press, fuse.
• Bharat mein gharelu supply: 220 V, 50 Hz AC.
• Taar ke rang (NCERT): Live — laal, Neutral — kaala, Earth — hara. (Naye IEC standard mein: live brown, neutral blue, earth hara-peela.) Earthing — dhatu ki body wale upkaran (fridge, press) ko shock se bachana.
• Bijli ke taar par baithi chidiya ko shock nahi — dono pairon ke beech vibhavaantar lagbhag zero.
• DC (disha nahi badalti — cell, battery) vs AC (disha baar-baar badalti — ghar). AC → DC = rectifier (diode); DC → AC = inverter.

10.4 चालक, अचालक, अर्धचालक (Band Theory)

• Chaalak (conductor): conduction band aur valence band overlap karte hain → free electrons.
• Kuchaalak (insulator): bada urja antaraal (> 3 eV) — lakdi, rubber, plastic, kaanch.
• Ardhchaalak (semiconductor): chhota antaraal (silicon ~1.1 eV, germanium ~0.7 eV); taap badhne par chalakta badhti. n-type = pancha-sanyojak (P, As) ki doping; p-type = tri-sanyojak (B, Al, Ga). Diode, transistor, solar cell, LED, chips.

📌 11. चुंबकत्व व विद्युत-चुंबकीय प्रेरण (Magnetism & EMI) (10 min read) — 2025 mein sabse zyada (11 Qs)!

11.1 चुंबक व क्षेत्र रेखाएँ

• Swatantra latka chumbak uttar-dakshin disha mein rukta hai. Samaan dhruv pratikarshan. Prithvi ka bhaugolik uttar ke paas chumbakiya dakshin dhruv hai.
• Kshetra rekhaayen: chumbak ke bahar N → S, andar S → N; hamesha band loop (closed loops); kabhi ek-doosre ko kaat-ti nahi; jahan ghani wahan kshetra tez.
• Chumbakiya kshetra (B) ki unit tesla (T); chumbakiya flux ki weber (Wb).
• Padarth: Lauh-chumbakiya (ferro) — loha, cobalt, nickel; anuchumbakiya (para) — aluminium, platinum; pratichumbakiya (dia) — bismuth, tamba, paani. Naram loha → vidyut-chumbak (jaldi chumbak banta/hat-ta); steel → sthaayi chumbak.

11.2 धारा का चुंबकीय प्रभाव

• Oersted (1820): dhara wale taar ke paas compass ki sui vikshepit → bijli se chumbak.
• Disha: Dakshin-hast angustha niyam (Right-hand thumb rule).
• Parinalika (Solenoid): andar kshetra ek-samaan (uniform); bahar kshetra chhad chumbak / dwidhruv (dipole) jaisa. Dhara ulti → kshetra ki disha ulti. Naram lohe ki core → vidyut chumbak (crane, electric ghanti, MRI).

11.3 धारावाही चालक पर बल व मोटर

• F = B I L sin θ → θ = 90° par adhiktam (F = BIL), θ = 0° ya 180° par zero. I double aur B triple → F 6 guna.
• Fleming ka vaam-hast (Left-hand) niyam (motor): Tarjani (forefinger) = Field, Madhyama (middle) = Current, Angootha (thumb) = Motion/Force. Yaad: F-B-I → thumb F(orce), fore B, middle I.
• Vidyut motor: vidyut → yantrik urja (pankha, mixer, washing machine).

11.4 विद्युत-चुंबकीय प्रेरण (EMI)

• Faraday (1831): kundali se guzarte chumbakiya flux ke badalne par prerit emf/dhara. Flux Φ = B A cos θ, θ = B aur kshetrafal ke abhilamb (normal) ke beech kon → flux adhiktam jab B satah ke lambvat ho.
• Lenz ka niyam: prerit dhara us kaaran ka virodh karti hai jisse wo bani (urja sanrakshan). Chumbak paas laane par kundali pratikarshan karti hai.
• Chalte chaalak mein emf ka kaaran — mukt aaveshon par Lorentz bal (qv × B).
• Fleming ka dakshin-hast (Right-hand) niyam → generator/dynamo (yantrik → vidyut).
• Transformer: paraspar prerakatv; sirf AC par kaam karta; V_s/V_p = N_s/N_p. Step-up (voltage badhaaye) / step-down (ghataaye). Door bijli bhejne ke liye voltage badhaate hain (nuksaan kam).

📌 12. आधुनिक भौतिकी (Modern Physics Basics) (6 min read)

12.1 विद्युत-चुंबकीय स्पेक्ट्रम (EM Spectrum)

Tarang-dairghya badhte kram mein (aavritti/urja ghat-te kram mein):

Sabhi EM tarangen nirvaat mein 3 × 10⁸ m/s se chalti hain. Dhwani, alpha, beta EM tarangen nahi hain.

12.2 नाभिकीय भौतिकी (Nuclear)

• E = mc² (Einstein) — dravyaman ka urja mein rupantaran.
• नाभिकीय विखंडन (Fission): bhaari naabhik (U-235) mand (slow) neutron se toot-ta hai → 2 madhyam naabhik + 2–3 neutron + ~200 MeV urja → shrinkhla abhikriya (chain reaction). Aniyantrit = parmaanu bomb; niyantrit = parmaanu reactor.
• Reactor mein: mandak (moderator) — bhaari jal (D₂O)/graphite, neutron dheeme karta; niyantran chhad (control rods) — cadmium/boron, neutron sokhti; sheetlak (coolant).
• नाभिकीय संलयन (Fusion): halke naabhik (hydrogen isotopes) judkar helium — atyadhik taap chahiye (~10⁷ K). Surya/taaron ki urja, hydrogen bomb.
• Prakash-vidyut prabhav (Photoelectric): prakash se dhatu ki satah se electron nikalna — Einstein ko Nobel 1921 isi par (saapekshata par nahi). Solar cell.

📌 13. यंत्र, आविष्कार व वैज्ञानिक (Instruments, Inventions & Scientists) (6 min read)

13.1 मापक यंत्र (Instruments)

13.2 पुलिस से जुड़े उपकरण (Police-relevant)

13.3 आविष्कार (Inventions)

13.4 भारतीय वैज्ञानिक (Indian Scientists)

13.5 इकाइयाँ किसके नाम पर (Units after Scientists)

Newton (बल), Joule (कार्य/ऊर्जा), Watt (शक्ति), Pascal (दाब), Ampere (धारा), Volt (विभव), Ohm (प्रतिरोध), Coulomb (आवेश), Hertz (आवृत्ति), Tesla (चुंबकीय क्षेत्र), Weber (फ्लक्स), Kelvin (ताप), Farad (धारिता).