Class 12 · Physics · English medium · Part 1
Class 12 Physics Part 1 companion
Textbook for Class XII
An interactive companion to Class 12 Physics Part 1: original explanations, field and circuit simulations, step-by-step derivations, worked examples and practice.
Hindi medium: भौतिकी भाग 1
An original companion to Physics, NCERT Class 12 Physics (2026–27 edition). Official textbook ↗ ncert.nic.in
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Chapters
- ENHinglish
Chapter 1: Electric Charges and Fields
Class 12 Physics chapter 1 introduces electrostatics. - ENHinglish
Chapter 2: Electrostatic Potential and Capacitance
Class 12 Physics chapter 2. - ENHinglish
Chapter 3: Current Electricity
Current is the rate of flow of charge. - ENHinglish
Chapter 4: Moving Charges and Magnetism
Moving charges make magnetic fields and feel magnetic forces. - ENHinglish
Chapter 5: Magnetism and Matter
Poles come in pairs; field lines are closed loops (S to N inside a magnet). - ENहिंHinglish
Chapter 6: Electromagnetic Induction
A changing magnetic flux through a circuit induces an emf. - ENHinglish
Chapter 7: Alternating Current
Alternating voltage (India: 50 Hz, 230 V rms). - ENHinglish
Chapter 8: Electromagnetic Waves
Ampère's law fails for a charging capacitor; Maxwell added the displacement current , giving the Ampère–Maxwell law.
Also in हिन्दी / Hinglish
- Chapter 1: Electric Charges and Fields (Hinglish)
- Chapter 2: Electrostatic Potential and Capacitance (Hinglish)
- Chapter 3: Current Electricity (Hinglish)
- Chapter 4: Moving Charges and Magnetism (Hinglish)
- Chapter 5: Magnetism and Matter (Hinglish)
- Chapter 6: वैद्युतचुंबकीय प्रेरण (हिन्दी) · Electromagnetic Induction (Hinglish)
- Chapter 7: Alternating Current (Hinglish)
- Chapter 8: Electromagnetic Waves (Hinglish)
A
ac generatorप्रत्यावर्ती धारा जनित्रA machine that turns a coil in a magnetic field, converting mechanical energy into an alternating emf.Ch 6 · Electromagnetic Inductionalternating current (ac)प्रत्यावर्ती धाराA current (or voltage) that varies sinusoidally with time and reverses direction every half cycle, such as i = im sin ω t.Ch 7 · Alternating Currentampereऐम्पियरThe SI unit of current, formerly defined by the force of 2 × 10⁻⁷ N per metre between two parallel wires 1 m apart.Ch 4 · Moving Charges and MagnetismAmpère–Maxwell lawऐम्पियर-मैक्सवेल नियम∮ B · d l = μ0 ic + μ0 ε0 d ΦE/dt: currents and changing electric flux produce magnetic fields.Ch 8 · Electromagnetic WavesAmpère's circuital lawऐम्पियर का परिपथीय नियमThe line integral of B round any closed curve equals μ0 times the net current through it: ∮ B · d l = μ0 I.Ch 4 · Moving Charges and MagnetismAmperian loopऐम्पियरी पाशA closed curve chosen so that along each part B is tangential and constant, perpendicular, or zero, making Ampère's law easy to apply.Ch 4 · Moving Charges and Magnetismantennaऐन्टेनाA conductor in which oscillating charges send out, or are driven by, electromagnetic waves.Ch 8 · Electromagnetic WavesB
back emfThe self-induced emf in a coil, which opposes any change in the current through it.Ch 6 · Electromagnetic InductionBiot–Savart lawबायो-सावर्ट नियमThe field of a current element: d B = (μ0/4 π) I d l × r/r³.Ch 4 · Moving Charges and MagnetismC
capacitanceधारिताThe ratio C = Q/V of a capacitor's charge to its potential difference; measured in farads.Ch 2 · Electrostatic Potential and Capacitancecapacitive reactanceधारितीय प्रतिघातXC = 1/ω C, the opposition of a capacitor to ac, in ohms; it falls as frequency rises.Ch 7 · Alternating Currentcapacitorसंधारित्रTwo conductors separated by an insulator, used to store equal and opposite charges and electrical energy.Ch 2 · Electrostatic Potential and Capacitancecharge densityआवेश घनत्वCharge per unit length (λ), area (σ) or volume (ρ).Ch 1 · Electric Charges and Fieldsconduction currentचालन धाराCurrent carried by moving charges, such as electrons in a wire.Ch 8 · Electromagnetic WavesconductivityचालकताThe reciprocal of resistivity, σ = 1/ρ, in siemens per metre, with j = σ E.Ch 3 · Current ElectricityconductorचालकA material in which charge moves freely, such as a metal.Ch 1 · Electric Charges and Fieldsconservation of chargeआवेश संरक्षणThe total charge of an isolated system never changes.Ch 1 · Electric Charges and Fieldsconservative forceसंरक्षी बलA force whose work between two points does not depend on the path taken, so that a potential energy can be defined for it.Ch 2 · Electrostatic Potential and CapacitanceCoulomb's lawकूलॉम का नियमThe force between two point charges is proportional to q1q2 and to 1/r², along the line joining them.Ch 1 · Electric Charges and FieldsCurie temperatureक्यूरी तापThe temperature above which a ferromagnet loses its domains and becomes paramagnetic: about 1043 K for iron.Ch 5 · Magnetism and Mattercurrent densityधारा घनत्वCurrent per unit area of a surface normal to the flow, j = I/A, in A/m². It is a vector.Ch 3 · Current Electricitycurrent sensitivityधारा सुग्राहिताThe deflection of a galvanometer per unit current, ϕ/I = NAB/k.Ch 4 · Moving Charges and Magnetismcyclotron frequencyसाइक्लोट्रॉन आवृत्तिThe frequency νc = qB/2 π m with which a charged particle circles in a uniform magnetic field; it does not depend on the particle's speed.Ch 4 · Moving Charges and MagnetismD
diamagneticप्रतिचुंबकीयHaving a small negative χ: weakly magnetised against the field and pushed towards weaker fields.Ch 5 · Magnetism and Matterdielectricपरावैद्युतAn insulating material whose bound charges shift or turn in a field, partly cancelling the field inside it.Ch 2 · Electrostatic Potential and Capacitancedielectric constantपरावैद्युतांकThe factor K = ε/ε0 by which filling a capacitor with a material raises its capacitance.Ch 2 · Electrostatic Potential and Capacitancedielectric strengthपरावैद्युत सामर्थ्यThe largest field an insulator can bear before it breaks down; about 3×10⁶ V/m for dry air.Ch 2 · Electrostatic Potential and Capacitancedipole momentद्विध्रुव आघूर्णp = 2qa, directed from -q to +q; SI unit C m.Ch 1 · Electric Charges and Fieldsdisplacement currentविस्थापन धाराThe term id = ε0 d ΦE/dt in the Ampère–Maxwell law: a changing electric flux that produces a magnetic field like a current, although no charge flows.Ch 8 · Electromagnetic WavesdomainडोमेनA region of a ferromagnet in which all the atomic moments point the same way.Ch 5 · Magnetism and Matterdrift velocityअपवाह वेगThe small average velocity of charge carriers in a field, v d = -e τ E/m for electrons, on top of their random motion.Ch 3 · Current ElectricityE
eddy currentsभँवर धाराएँLoops of induced current that circulate inside a solid piece of metal when the flux through it changes.Ch 6 · Electromagnetic Inductionelectric chargeविद्युत आवेशA property of matter that makes it exert and feel electric forces; it is positive or negative, and like charges repel.Ch 1 · Electric Charges and Fieldselectric currentविद्युत धाराThe net charge crossing a surface per unit time, I = d Q/d t, measured in amperes.Ch 3 · Current Electricityelectric dipoleविद्युत द्विध्रुवTwo equal and opposite charges ± q a small distance 2a apart.Ch 1 · Electric Charges and Fieldselectric fieldविद्युत क्षेत्रThe force per unit positive test charge at a point, E = F/q0, in N/C.Ch 1 · Electric Charges and Fieldselectric field lineविद्युत क्षेत्र रेखाA curve whose tangent gives the field direction; crowded lines mean a strong field.Ch 1 · Electric Charges and Fieldselectric fluxविद्युत फ्लक्स∑ E · Δ S over a surface; a measure of the field lines crossing it.Ch 1 · Electric Charges and Fieldselectromagnetic inductionवैद्युतचुंबकीय प्रेरणThe production of an emf in a circuit whenever the magnetic flux through it changes.Ch 6 · Electromagnetic Inductionelectromagnetic spectrumवैद्युतचुंबकीय स्पेक्ट्रमThe whole range of electromagnetic waves arranged by frequency or wavelength, from radio waves to gamma rays.Ch 8 · Electromagnetic Waveselectromagnetic waveवैद्युतचुंबकीय तरंगA self-sustaining pattern of oscillating electric and magnetic fields, perpendicular to each other and to the direction of travel, moving at c in vacuum.Ch 8 · Electromagnetic Waveselectron voltइलेक्ट्रॉन वोल्टThe energy change of a charge e moving through 1 V: 1 eV = 1.6×10⁻¹⁹ J.Ch 2 · Electrostatic Potential and Capacitanceelectrostatic potentialस्थिरवैद्युत विभवWork per unit positive test charge to bring the charge from infinity to a point; measured in volts (1 V = 1 J/C).Ch 2 · Electrostatic Potential and Capacitanceelectrostatic potential energyस्थिरवैद्युत स्थितिज ऊर्जाThe work needed to bring a charge, or to assemble a set of charges, from infinity without acceleration.Ch 2 · Electrostatic Potential and Capacitanceelectrostatic shieldingस्थिरवैद्युत परिरक्षणThe absence of electric field inside an empty cavity in a conductor, whatever the charges and fields outside.Ch 2 · Electrostatic Potential and Capacitanceemfविद्युत वाहक बलThe terminal potential difference of a source on open circuit: the work its chemical (or other) action does per unit charge. Measured in volts.Ch 3 · Current Electricityenergy densityऊर्जा घनत्वEnergy stored per unit volume of an electric field, u = 12 ε0E².Ch 2 · Electrostatic Potential and Capacitanceequipotential surfaceसमविभव पृष्ठA surface on which the potential has the same value everywhere; the field crosses it at right angles.Ch 2 · Electrostatic Potential and CapacitanceF
Faraday's lawफैराडे का नियमThe emf induced in a circuit equals minus the rate of change of the flux linked with it, ε = -N d ΦB/dt.Ch 6 · Electromagnetic InductionferromagneticलौहचुंबकीयHaving a very large χ because atomic moments line up in domains; strongly attracted and able to become a permanent magnet.Ch 5 · Magnetism and Matterflux linkageThe total flux through all the turns of a coil; N ΦB when each of its N turns links the same flux ΦB.Ch 6 · Electromagnetic InductionG
gamma raysगामा किरणेंThe shortest electromagnetic waves, emitted by atomic nuclei.Ch 8 · Electromagnetic WavesGaussian surfaceगाउसीय पृष्ठAn imaginary closed surface used to apply Gauss's law.Ch 1 · Electric Charges and FieldsH
henryहेनरीThe SI unit of inductance: 1 H = 1 Wb/A = 1 V s/A.Ch 6 · Electromagnetic InductionI
impedanceप्रतिबाधाThe ratio Z = V/I for an ac circuit; for series LCR, Z = √ R² + (XC - XL)².Ch 7 · Alternating Currentinductanceप्रेरकत्वFlux linkage per unit current, fixed by the geometry of the coils and the material of their core.Ch 6 · Electromagnetic Inductioninductive reactanceप्रेरकीय प्रतिघातXL = ω L, the opposition of an inductor to ac, in ohms; it rises with frequency.Ch 7 · Alternating Currentinfraredअवरक्तWaves from about 700 nm to 1 mm, given out by warm objects; they set molecules vibrating and so heat what absorbs them.Ch 8 · Electromagnetic Wavesinsulatorविद्युतरोधीA material in which charges cannot move freely, such as glass or plastic.Ch 1 · Electric Charges and Fieldsinternal resistanceआंतरिक प्रतिरोधThe resistance r inside a cell, such as that of its electrolyte, which causes a drop Ir when a current flows.Ch 3 · Current ElectricityK
Kirchhoff's rulesTwo circuit rules: the currents into a junction equal those out, and the potential changes round any closed loop add to zero.Ch 3 · Current ElectricityL
Lenz's lawलेंज़ का नियमAn induced current circulates so that its own field works against the change of flux that caused it.Ch 6 · Electromagnetic InductionLorentz forceलोरेंज बलThe combined electric and magnetic force q(E + v × B) acting on a point charge that moves through both fields.Ch 4 · Moving Charges and MagnetismM
magnetic dipoleचुंबकीय द्विध्रुवA pair of equal and opposite poles, or a small current loop, whose far field falls as 1/r³; a bar magnet is one.Ch 5 · Magnetism and Mattermagnetic field lineचुंबकीय क्षेत्र रेखाA curve whose tangent at every point gives the direction of B; the lines form closed loops and never cross.Ch 5 · Magnetism and Mattermagnetic fluxचुंबकीय फ्लक्सA measure of the magnetic field passing through a surface; ΦB = BA cos θ for a flat surface in a uniform field.Ch 6 · Electromagnetic Inductionmagnetic intensityचुंबकीय तीव्रताH = B/μ0 - M, set by free currents alone; H = nI in a long solenoid.Ch 5 · Magnetism and Mattermagnetic momentचुंबकीय आघूर्णFor a flat coil, m = NI A in A m²; in a field B it feels a torque m × B.Ch 4 · Moving Charges and Magnetismmagnetic momentचुंबकीय आघूर्णThe vector m that measures the strength and direction of a magnetic dipole; m = NIA for a coil, in A m².Ch 5 · Magnetism and Mattermagnetic monopoleचुंबकीय एकल ध्रुवA hypothetical isolated N or S pole. None has ever been found, which is why ∮ B · d S = 0.Ch 5 · Magnetism and Mattermagnetic poleचुंबकीय ध्रुवEither end of a magnet, where its field lines leave (N pole) or enter (S pole) and where its pull is strongest.Ch 5 · Magnetism and Mattermagnetic susceptibilityचुंबकीय प्रवृत्तिThe dimensionless ratio χ = M/H: how strongly a material is magnetised by a given H.Ch 5 · Magnetism and MattermagnetisationचुंबकनThe net magnetic moment per unit volume of a material, M, in A/m.Ch 5 · Magnetism and MatterMaxwell's equationsमैक्सवेल समीकरणThe four laws (Gauss's laws for E and B, Faraday's law and the Ampère–Maxwell law) that describe how electric and magnetic fields arise.Ch 8 · Electromagnetic WavesMeissner effectमाइसनर प्रभावThe complete expulsion of a weak magnetic field from a superconductor, which behaves as a perfect diamagnet with χ = -1.Ch 5 · Magnetism and Mattermicrowavesसूक्ष्म तरंगेंShort radio waves, roughly 1 mm to 10 cm long (the boundary is loose), used in radar, ovens and Wi-Fi.Ch 8 · Electromagnetic WavesmobilityगतिशीलताDrift speed per unit field, μ = vd/E = e τ/m, in m² V⁻¹ s⁻¹.Ch 3 · Current Electricitymotional emfगतिक विद्युत वाहक बलThe emf of a conductor moving through a magnetic field; Blv for a rod moving at right angles to B.Ch 6 · Electromagnetic Inductionmoving coil galvanometerचल कुंडली धारामापीAn instrument in which a coil in a radial magnetic field turns against a spring through an angle proportional to the current.Ch 4 · Moving Charges and Magnetismmutual inductanceअन्योन्य प्रेरकत्वFlux linkage with one coil per unit current in a neighbouring coil; it gives ε1 = -M dI2/dt.Ch 6 · Electromagnetic InductionP
paramagneticअनुचुंबकीयHaving a small positive χ due to permanent atomic moments: weakly pulled towards stronger fields.Ch 5 · Magnetism and Matterpermeability of free spaceनिर्वात की चुंबकशीलताThe constant μ0 = 4 π × 10⁻⁷ T m/A in the laws of magnetism, playing the role that ε0 plays in electrostatics.Ch 4 · Moving Charges and Magnetismphasorफेज़रA rotating arrow representing a sinusoidal quantity: its length is the amplitude and its vertical projection is the instantaneous value.Ch 7 · Alternating Currentphotonफ़ोटॉनA packet of electromagnetic energy h ν.Ch 8 · Electromagnetic Wavespitch (of a helix)चूड़ी अंतरालThe distance a charged particle moves along the magnetic field during one turn of its helical path, p = v∥ T.Ch 4 · Moving Charges and Magnetismpolar moleculeध्रुवीय अणुA molecule with a permanent dipole moment, such as water.Ch 1 · Electric Charges and Fieldspolar moleculeध्रुवीय अणुA molecule whose centres of positive and negative charge are permanently separated, giving it a dipole moment of its own.Ch 2 · Electrostatic Potential and Capacitancepolarisationध्रुवणThe dipole moment per unit volume that a dielectric develops in an electric field.Ch 2 · Electrostatic Potential and Capacitancepower factorशक्ति गुणांकcos ϕ in P = VI cos ϕ; equal to R/Z for a series LCR circuit.Ch 7 · Alternating CurrentQ
quality factor (Q)Q = ω0 L/R, a pure number measuring how sharp the resonance peak is.Ch 7 · Alternating Currentquantisation of chargeआवेश का क्वांटमीकरणEvery free charge is a whole-number multiple of e = 1.6×10⁻¹⁹ C: q = ne.Ch 1 · Electric Charges and FieldsR
radio wavesरेडियो तरंगेंElectromagnetic waves longer than about 10 cm, made by charges oscillating in antennas and circuits.Ch 8 · Electromagnetic Wavesrelative permeabilityआपेक्षिक चुंबकशीलताμr = 1 + χ = μ/μ0, the factor by which a linear material multiplies μ0 H.Ch 5 · Magnetism and Matterrelaxation timeThe average time τ since the last collision of the conduction electrons; about 10⁻¹⁴ s in metals.Ch 3 · Current Electricityresistanceप्रतिरोधThe ratio R = V/I for a conductor, measured in ohms (Ω).Ch 3 · Current Electricityresistivityप्रतिरोधकताThe material property ρ in R = ρ l/A, in Ω m. It depends on the material and temperature, not on shape.Ch 3 · Current ElectricityresonanceअनुनादThe large response of a system driven at its natural frequency; in a series LCR circuit, the current peak when XL = XC.Ch 7 · Alternating Currentresonant frequencyअनुनादी आवृत्तिThe frequency at which a series LCR circuit resonates: ω0 = 1/√ LC.Ch 7 · Alternating Currentrms valueवर्ग माध्य मूल मानThe square root of the mean of the square over a cycle; for a sine wave, the peak value divided by √ 2.Ch 7 · Alternating CurrentS
self-inductanceस्वप्रेरकत्वFlux linkage with a coil per unit current in the same coil; it gives ε = -L dI/dt.Ch 6 · Electromagnetic InductionshuntशंटA low resistance placed across a galvanometer coil, in parallel, which carries most of the current and turns the galvanometer into an ammeter.Ch 4 · Moving Charges and MagnetismsolenoidपरिनालिकाA long wire wound in a closely spaced helix; inside a long solenoid the field is uniform, B = μ0 nI.Ch 4 · Moving Charges and Magnetismsuperposition principleअध्यारोपण सिद्धांतThe total force (or field) from several charges is the vector sum of the separate contributions.Ch 1 · Electric Charges and FieldsT
temperature coefficient of resistivityप्रतिरोधकता ताप गुणांकThe fractional change in resistivity per degree, α in ρT = ρ0[1 + α (T - T0)]. Positive for metals.Ch 3 · Current Electricityterminal voltageThe potential difference across a source while it supplies a current I: V = ε - Ir.Ch 3 · Current Electricityteslaटेस्लाThe SI unit of magnetic field: 1 T = 1 N A⁻¹ m⁻¹. One gauss is 10⁻⁴ T.Ch 4 · Moving Charges and Magnetismtransformerट्रांसफ़ॉर्मरA device with two coils on a shared iron core that changes an ac voltage by mutual induction: Vs/Vp = Ns/Np.Ch 7 · Alternating CurrentU
ultravioletपराबैंगनीWaves from about 400 nm down to 1 nm, energetic enough to break chemical bonds.Ch 8 · Electromagnetic WavesV
voltage sensitivityवोल्टता सुग्राहिताThe deflection of a galvanometer per unit voltage across it, ϕ/V = NAB/kR.Ch 4 · Moving Charges and MagnetismW
wattless currentवाटहीन धाराA current that is 90 ° out of phase with the voltage, so it carries no average power.Ch 7 · Alternating Currentwave numberतरंग संख्याk = 2 π/λ, the change of phase per unit distance along a wave.Ch 8 · Electromagnetic WavesweberवेबरThe SI unit of magnetic flux: 1 Wb = 1 T m².Ch 6 · Electromagnetic InductionWheatstone bridgeव्हीटस्टोन सेतुFour resistors in a diamond, with a cell across one diagonal and a galvanometer across the other. It balances when P/Q = R/S.Ch 3 · Current ElectricityX
X-raysएक्स-किरणेंWaves from about 10 nm down to 10⁻¹³ m, produced when fast electrons are stopped in a metal target.Ch 8 · Electromagnetic Wavesncert.ai is an independent learning companion aligned to the NCERT curriculum. It is not affiliated with or endorsed by NCERT.