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Free Physics shorts

भौतिकी · طبیعیات

22 topics, each a handful of cards plus practice questions with explanations. Free to read in full — no sign-up. Counts for TRE-4, STET, BPSC PCS, RRB NTPC, SSC CGL.

22 shorts · 176 practice questions

• Atoms and Nuclei — Radioactivity, Half-Life, and Why Fission and Fusion Both Release Energyपरमाणु एवं नाभिक — रेडियोसक्रियता, अर्द्ध-आयु, और विखंडन तथा संलयन दोनों से ऊर्जा क्यों निकलती हैThe nucleus is a hundred-thousand times smaller than the atom yet carries almost all of its mass, and the questions papers ask about it are finite. Alpha is a helium nucleus — most ionising, least penetrating, stopped by paper; beta is an electron stopped by aluminium; gamma is an electromagnetic wave stopped only by thick lead. Alpha emission drops the atomic number by 2 and the mass number by 4; beta emission raises the atomic number by 1 and leaves the mass number untouched; gamma changes neither. After n half-lives what remains is N0 divided by 2 raised to n, so 160 g with a 3-hour half-life leaves 10 g after 12 hours. Binding energy per nucleon peaks near iron-56, which is why splitting heavy nuclei and joining light ones both release energy — fission runs our reactors, fusion runs the Sun. Three traps repeat: alpha called most penetrating, beta said to lower the atomic number, and control rods described as slowing neutrons when they absorb them.6 CARDS · 8 QUESTIONS
• Dispersion and Scattering of Light — Why the Sky Is Blue, the Sunset Red and the Road Looks Wetप्रकाश का वर्ण-विक्षेपण और प्रकीर्णन — आकाश नीला, सूर्यास्त लाल और सड़क गीली क्यों दिखती हैSix everyday sights — blue sky, red sunset, rainbow, mirage, twinkling stars, red danger signals — are all answered by two ideas: shorter wavelengths bend and scatter more, longer ones travel farther. Learn the pair and the whole question set collapses.6 CARDS · 8 QUESTIONS
• Electricity — Ohm's Law, Series vs Parallel and the Household Circuitविद्युत — ओम का नियम, श्रेणी बनाम समांतर और घरेलू परिपथV = IR, P = VI = I²R = V²/R, series adds resistance while parallel cuts it. Five formulas, one wiring diagram, and the bulb question every paper reprints.6 CARDS · 8 QUESTIONS
• Electrostatics — Coulomb's Law, Capacitance and Why a Lightning Conductor Is Pointedस्थिर वैद्युतिकी — कूलॉम का नियम, धारिता और तड़ितचालक नुकीला क्यों होता हैCharge at rest runs the comb that lifts paper and the rod that saves a building from lightning. Four formulas — F = kq₁q₂/r², E = F/q, V = W/q, C = Q/V — plus one rule most students get backwards: capacitors add in parallel, not in series.6 CARDS · 8 QUESTIONS
• Gravitation — small g vs capital G, Weight, and Escape Velocityगुरुत्वाकर्षण — छोटा g बनाम बड़ा G, भार और पलायन वेगOne letter decides half the marks in this chapter. G is a universal constant, 6.67 × 10⁻¹¹ N m² kg⁻², the same everywhere in the universe; g is acceleration due to gravity, 9.8 m s⁻², and it changes with latitude, altitude and depth. Inverse-square law, mass vs weight, g on the Moon, g = GM/R², escape velocity 11.2 km/s and orbital velocity 7.9 km/s — plus the exact traps SSC, Railway NTPC, BPSC TRE-4, CTET and UPSC set.6 CARDS · 8 QUESTIONS
• Heat and Temperature — Specific Heat, Latent Heat and the Three Ways Heat Travelsऊष्मा और ताप — विशिष्ट ऊष्मा, गुप्त ऊष्मा और ऊष्मा के तीन संचरण मार्गWhy heat and temperature are not the same thing, the C–F–K conversion that solves every scale question, Q = mcΔT and Q = mL worked out with numbers, why steam burns worse than boiling water, and why fish survive under a frozen lake. Written for the general science sections of BPSC TRE-4, CTET, SSC CGL, Railway NTPC and UPSC Prelims.6 CARDS · 8 QUESTIONS
• Heating Effect of Current: Joule's Law, Power Formulas, the kWh Bill and the Fuseधारा का ऊष्मीय प्रभाव: जूल का नियम, शक्ति के सूत्र, kWh बिल और फ्यूज़H = I²Rt, P = VI = I²R = V²/R, 1 kWh = 3.6 × 10⁶ J, and why the lower-watt bulb glows brighter in series: the heating-effect formulas and traps that physics papers repeat.6 CARDS · 8 QUESTIONS
• Inventions and Discoveries — A Hundred Names, Sorted So You Can Actually Keep Themआविष्कार और खोजें — सौ नाम, ऐसे छाँटे हुए कि वे सचमुच याद रह जाएँThis is not a chapter, it is a list — and lists are lost by revising them in alphabetical order. Sort by field, learn discoveries and inventions separately, and keep the confusable pairs side by side rather than apart.6 CARDS · 8 QUESTIONS
• Light — Mirrors, Lenses and the Two Formulae That Solve Bothप्रकाश — दर्पण, लेंस और वे दो सूत्र जो दोनों हल कर देते हैंMirror formula, lens formula, magnification, power in dioptres, critical angle and dispersion — the six ideas behind almost every optics question in SSC, Railway, CTET and teacher-recruitment papers.6 CARDS · 8 QUESTIONS
• Magnetism and Electromagnetic Induction — Field Lines, Motor, Generator and Transformerचुंबकत्व एवं विद्युत चुंबकीय प्रेरण — क्षेत्र रेखाएँ, मोटर, जनित्र और ट्रांसफार्मरTwo sentences run this whole chapter: current makes a field, a changing field makes current. Left hand for the motor, right hand for the generator — and the exam lives in that one swap.6 CARDS · 8 QUESTIONS
• Modes of Heat Transfer — Conduction, Convection and Radiationऊष्मा स्थानांतरण की विधियाँ — चालन, संवहन और विकिरणWhy does a steel spoon burn your fingers while a wooden one doesn't? Why do sea breezes blow by day and land breezes by night? Why is a vacuum flask silvered? One idea — heat moves by conduction, convection or radiation — answers all of them, and exams love asking which mode is at work.6 CARDS · 8 QUESTIONS
• Motion — Distance vs Displacement, the Three Equations, and Reading Graphsगति — दूरी बनाम विस्थापन, गति के तीन समीकरण और ग्राफ़ पढ़नाDistance is how far you walked; displacement is how far you ended up. Three equations solve almost every numerical, and two graphs answer the rest — slope and area are the whole trick.6 CARDS · 8 QUESTIONS
• Newton's Three Laws — And What Each One Actually Explainsन्यूटन के तीन नियम — और प्रत्येक वास्तव में क्या समझाता हैFirst law explains why you lurch forward when a bus brakes. Second gives F = ma. Third is why a rocket moves. Three laws, most of mechanics.6 CARDS · 8 QUESTIONS
• Pressure, Density and Floatation — Pascal's Law, Archimedes' Principle and Bernoulliदाब, घनत्व एवं प्लवन — पास्कल का नियम, आर्किमिडीज़ का सिद्धांत और बर्नूलीThree formulas run this whole chapter: P = F/A, P = hρg and upthrust = weight of fluid displaced. Liquid pressure never depends on area or shape, a hydraulic press multiplies force but not work, and floating ice melting leaves the water level exactly where it was. Ice floats 9/10 under, 1/10 above.6 CARDS · 8 QUESTIONS
• Properties of Matter — Elasticity, Surface Tension, Viscosity and Why Water Climbs a Thin Tubeपदार्थ के गुण — प्रत्यास्थता, पृष्ठ तनाव, श्यानता और पानी पतली नली में क्यों चढ़ता हैSteel is more elastic than rubber, raindrops are round, and honey slows down while hot gas speeds up. Three properties — elasticity, surface tension and viscosity — explain all of it, and papers ask about them every year.6 CARDS · 8 QUESTIONS
• Satellites and Orbits: Kepler's Laws, Orbital Velocity, Geostationary vs Polar and ISRO Launchersउपग्रह और कक्षाएँ: केपलर के नियम, कक्षीय वेग, भूस्थिर बनाम ध्रुवीय और ISRO प्रक्षेपण यानA satellite is a falling object that keeps missing the Earth: learn the orbit speed, Kepler's three laws, why geostationary and polar satellites differ and which ISRO rocket does what.6 CARDS · 8 QUESTIONS
• Simple Machines, Levers and Mechanical Advantage — Force Multiplied Is Distance Paidसरल मशीनें, उत्तोलक और यांत्रिक लाभ — बल जितना बढ़ेगा, दूरी उतनी चुकानी होगीA machine never creates energy — it trades force against distance. Learn where the fulcrum sits to name a lever's class, and one ratio, load over effort, answers every mechanical advantage question in the chapter.6 CARDS · 8 QUESTIONS
• Sound — v = fλ, the Echo Rule, SONAR and Why Ultrasound Is Everywhereध्वनि — v = fλ, प्रतिध्वनि का नियम, SONAR और अल्ट्रासाउंड हर जगह क्यों हैOne formula (v = fλ), one round-trip rule (2d = v × t) and one fact (sound needs a medium) cover almost every sound question SSC CGL/CHSL, Railway NTPC and Group D, BPSC TRE-4 and CTET set. Plus the speed order solids > liquids > gases, the 20–20,000 Hz audible range, and the 17.2 m minimum distance for a distinct echo.6 CARDS · 8 QUESTIONS
• The Electromagnetic Spectrum — The Order, the Uses and the Discoverersविद्युत चुंबकीय स्पेक्ट्रम — क्रम, उपयोग और खोजकर्ताSeven waves in one fixed order, one mnemonic, a use-and-discoverer table, and the fact half the candidates get wrong — that radio waves and gamma rays travel at exactly the same speed in vacuum. Built for the one-mark science questions in SSC, Railway, CTET and teacher-recruitment papers.6 CARDS · 8 QUESTIONS
• Total Internal Reflection, Optical Fibres and Optical Instrumentsपूर्ण आंतरिक परावर्तन, प्रकाशीय तंतु और प्रकाशीय यंत्रLight is totally reflected when it goes from a denser to a rarer medium beyond the critical angle, where sin C = 1/n. That one idea explains diamonds, optical fibres and prisms, and the same chapter covers microscope and telescope magnification formulas.6 CARDS · 8 QUESTIONS
• Units, Measurements and Scientific Instruments — SI Units and What Measures Whatमात्रक, मापन और वैज्ञानिक उपकरण — SI मात्रक और कौन क्या मापता हैSeven base units, the derived ones papers reuse, and the confusable instrument pairs: barometer vs manometer, hygrometer vs hydrometer, anemometer vs altimeter.6 CARDS · 8 QUESTIONS
• Work, Energy and Power — The Zero-Work Cases, KE ∝ v² and the kWh Trapकार्य, ऊर्जा और शक्ति — शून्य कार्य की स्थितियाँ, KE ∝ v² और kWh का जालFour formulas cover this whole chapter — W = Fs·cosθ, KE = ½mv², PE = mgh and P = W/t — but the marks are decided by three facts around them: work is zero whenever force and displacement are perpendicular, kinetic energy grows as the square of speed, and the kilowatt-hour is a unit of energy, not power. With the exact traps SSC CGL/CHSL, Railway NTPC/Group D, BPSC TRE-4, CTET and UPSC set on each.6 CARDS · 8 QUESTIONS