CBSE Class 12 Physics 2026: Electrostatics + Current Electricity (Top 20 Most Expected Q &A with Solutions)
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CBSE Class 12 Physics के Electrostatics और Current Electricity के सबसे महत्वपूर्ण 20 सवाल–जवाब, formulas, derivations और numericals के साथ।
Q1) Coulomb’s Law लिखिए और SI unit बताइए।
Solution:
F=4πε01r2q1q2
-
F की unit: Newton (N)
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ε0: permittivity of free space
-
Force line joining charges के along होता है।
Q2) Point charge के कारण Electric Field का सूत्र (vector form)।
Solution:
E=4πε01r2qr^
-
दिशा: +q से बाहर, −q की तरफ।
Q3) Electric Flux की परिभाषा और unit।
Solution:
ΦE=E⋅A=EAcosθ-
Unit: Nm2/C
Q4) Gauss Law लिखिए।
Solution:
∮E⋅dA=ε0Qenc-
Closed surface के अंदर कुल charge ही matter करता है।
Q5) Infinite plane sheet (surface charge density σ) का electric field निकालिए।
Solution (Gauss): Pillbox Gaussian surface लें
2EA=ε0σA⇒E=2ε0σQ6) Long straight line charge (linear density λ) का field।
Solution: Cylindrical Gaussian surface
E(2πrL)=ε0λL⇒E=2πε0rλQ7) Conducting sphere (charge Q, radius R) का potential अंदर/बाहर।
Solution:
Outside (r≥R):
Inside (r≤R):
V=4πε01RQ(constant)Q8) Capacitor की capacitance क्या है?
Solution:
C=VQ-
Unit: Farad (F)
Q9) Parallel plate capacitor की capacitance (air और dielectric k)।
Solution:
C=dε0A,C′=dkε0A=kCQ10) Capacitor में stored energy derive कीजिए।
Solution (steps):
dW=VdQ=CQdQ W=∫0QCQdQ=2CQ2Also:
U=21CV2=21QVQ11) Ohm’s Law + V–I graph का meaning।
Solution:
V=IRV–I graph straight line; slope = R।
Q12) Resistivity ρ और Resistance का relation।
Solution:
R=ρAL-
ρ unit: Ωm
Q13) Temperature dependence: R=R0(1+αΔT) का अर्थ।
Solution:
-
α = temperature coefficient
-
Metals में α>0, temperature बढ़े तो R बढ़ता है।
Q14) Series/Parallel combination formula।
Solution:
Series: Rs=R1+R2+…
Parallel: Rp1=R11+R21+…
Q15) Kirchhoff’s Laws लिखिए।
Solution:
-
Junction law: ∑I=0
-
Loop law: ∑ΔV=0
Q16) Wheatstone bridge balance condition।
Solution:
QP=SRBalance पर galvanometer current = 0।
Q17) Meter bridge में unknown resistance X निकालने का formula।
Solution: balance length l
RX=100−ll⇒X=R100−llQ18) Potentiometer principle + emf comparison।
Solution:
Potential gradient k=LV.
Q19) Drift velocity से current का relation।
Solution:
I=neAvdCurrent density:
J=nevdQ20) Electrical power के 3 forms।
Solution:
P=VI=I2R=RV2Tags: #CBSEPhysics #Class12 #Electrostatics #CurrentElectricity #MostExpectedQuestions
✅ POST 2 (Q21–Q40)
🔥 CBSE Class 12 Physics 2026: Magnetism + EMI (Top 20 Most Expected Q&A with Solutions)
Description: Moving charges, magnetic field, cyclotron, torque, EMI, Lenz law, motional emf, transformer—Top 20 board-focused Q&A with solutions.
Q21) Lorentz force लिखिए।
Solution:
F=q(E+v×B)
Q22) Current carrying conductor पर force।
Solution:
F=I(L×B),F=BILsinθ
Q23) Long straight wire का magnetic field।
Solution:
B=2πrμ0I
Q24) Circular loop center पर magnetic field।
Solution:
B=2Rμ0NI
Q25) Solenoid के अंदर field।
Solution:
B=μ0nI
जहाँ n=LN.
Q26) Charged particle uniform B में circular motion: radius।
Solution:
qvB=rmv2⇒r=qBmv
Q27) Cyclotron frequency।
Solution:
f=2πmqB
(Non-relativistic case)
Q28) Magnetic dipole moment (current loop)।
Solution:
m=NIA
Q29) Uniform B में dipole पर torque।
Solution:
τ=m×B,τ=mBsinθ
Q30) Biot–Savart law।
Solution:
dB=4πμ0r2Idl×r^
Q31) Ampere’s circuital law।
Solution:
∮B⋅dl=μ0Ienc
Q32) B, H, M relation।
Solution:
B=μ0(H+M)
Q33) Susceptibility χ की definition।
Solution:
M=χH
Q34) Dia/Para/Ferro (1–1 line difference)।
Solution:
-
Diamagnetic: χ<0, weak repulsion
-
Paramagnetic: χ>0, weak attraction
-
Ferromagnetic: very large χ, strong attraction, domains
Q35) Hysteresis loop किसलिए?
Solution:
-
Area = energy loss per cycle
-
Retentivity/Coercivity का idea
Q36) Faraday’s law of induction।
Solution:
ε=−dtdΦQ37) Lenz law का meaning।
Solution:
Induced current हमेशा flux change को oppose करता है (minus sign).
Q38) Self inductance और induced emf।
Solution:
Φ=LI,ε=−LdtdIQ39) Inductor में stored energy।
Solution:
U=21LI2Q40) Motional emf (rod length l speed v in B)।
Solution:
ε=Blv(जब v⊥B और rod ⊥v)
✅ POST 3 (Q41–Q60)
🔥 CBSE Class 12 Physics 2026: AC + EM Waves (Top 20 Most Expected Q&A with Solutions)
Description: AC circuits, RMS, reactance, resonance, power factor, transformer basics और EM waves—Top 20 board questions with solutions.
Q41) RMS value of AC current/voltage।
Solution:
Irms=2I0,Vrms=2V0
Q42) Inductive & capacitive reactance।
Solution:
XL=ωL,XC=ωC1
Q43) Series RLC impedance।
Solution:
Z=R2+(XL−XC)2
Q44) Resonance condition और resonant frequency।
Solution:
XL=XC⇒ω0=LC1,f0=2πLC1
Q45) Power factor और average power।
Solution:
cosϕ=ZR,Pavg=VrmsIrmscosϕ
Q46) Pure inductor/capacitor में average power क्यों 0?
Solution: ϕ=90∘⇒cosϕ=0⇒Pavg=0
Q47) Resonance पर current max क्यों?
Solution: Resonance पर XL=XC⇒Z=R minimum ⇒ I=V/Z maximum.
Q48) Quality factor Q।
Solution:
Q=Rω0L
High Q ⇒ sharp resonance.
Q49) Transformer voltage relation।
Solution:
VpVs=NpNs
Q50) Ideal transformer power relation।
Solution:
VpIp=VsIs
Q51) EM wave transverse क्यों?
Solution: Electric field E और magnetic field B दोनों wave direction के perpendicular होते हैं।
Q52) EM wave speed का formula।
Solution:
c=μ0ε01
Q53) EM spectrum order (low to high frequency)।
Solution:
Radio < Micro < IR < Visible < UV < X-ray < Gamma
Q54) Displacement current concept (1 line)।
Solution: Changing electric field का effect current जैसा होता है, capacitor gap में continuity बनाता है।
Q55) Poynting vector meaning।
Solution:
S=μ01E×B
Energy flow per unit area per unit time।
Q56) AC generator principle।
Solution: Rotating coil ⇒ flux बदलता ⇒ ε=ε0sinωt
Q57) Eddy currents: use + prevention।
Solution: Use: braking, induction furnace; Prevention: laminations, slotted core.
Q58) AC में choke coil क्यों use?
Solution: Current limit करता है लेकिन power loss कम (mainly inductive).
Q59) LCR circuit में phase relation।
Solution:
-
Inductor: V leads I
-
Capacitor: I leads V
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R: V and I in phase
Q60) Numerical (Resonant frequency): L=0.2H, C=50μF।
Solution:
f0=2πLC1 LC=0.2×50×10−6=10×10−6=10−5 LC=10−5=3.162×10−3 f0=2π(3.162×10−3)1≈0.019861≈50.3 Hz✅ POST 4 (Q61–Q80)
🔥 CBSE Class 12 Physics 2026: Ray Optics + Wave Optics (Top 20 Most Expected Q&A with Solutions)
Description: Mirrors, lenses, prism, TIR, fiber, YDSE, diffraction, polarization—Top 20 board questions with solved numericals.
Q61) Mirror formula लिखिए।
Solution:
f1=v1+u1
Q62) Lens formula लिखिए।
Solution:
f1=v1−u1
Q63) Magnification (lens)।
Solution:
m=hh′=uv
Q64) Power of lens।
Solution:
P=f1 (f in meter),unit: diopter
Q65) Lens maker formula।
Solution:
f1=(μ−1)(R11−R21)
Q66) Total internal reflection conditions।
Solution:
-
Denser → rarer medium
-
i>C
sinC=n1n2
Q67) Optical fiber working principle।
Solution: Repeated Total Internal Reflection (TIR) के कारण light guide होती है।
Q68) Prism में minimum deviation पर refractive index।
Solution:
n=sin(2A)sin(2A+Dm)
Q69) Refraction at spherical surface।
Solution:
vn2−un1=Rn2−n1
Q70) Combination of lenses in contact।
Solution:
F1=f11+f21⇒P=P1+P2
Q71) Numerical (lens): f=+20cm, u=−30cm. Find v।
Solution:
f1=v1−u1⇒201=v1−(−301)=v1+301 v1=201−301=603−2=601⇒v=+60cm
Q72) YDSE fringe width formula।
Solution:
β=dλD
Q73) Bright और dark fringe condition।
Solution:
Bright: Δ=nλ
Dark: Δ=(2n+1)2λ
Q74) YDSE numerical: λ=500nm, D=1m, d=0.5mm. Find β।
Solution:
β=dλD=0.5×10−3500×10−9×1=0.5×10−3500×10−9=1000×10−6=10−3m=1mm
Q75) Diffraction vs Interference (difference)।
Solution:
Interference: दो coherent sources
Diffraction: single slit/aperture के कारण spreading
Q76) Single slit diffraction minima condition।
Solution:
asinθ=mλ
Q77) Polarisation क्या साबित करता है?
Solution: Polarisation केवल transverse waves में होता है ⇒ light transverse है।
Q78) Brewster law।
Solution:
taniB=n
Q79) Malus law।
Solution:
I=I0cos2θ
Q80) Rayleigh scattering और blue sky।
Solution: Scattering ∝λ41 ⇒ छोटी λ (blue) ज्यादा scatter होती है।
✅ POST 5 (Q81–Q100)
🔥 CBSE Class 12 Physics 2026: Modern Physics + Semiconductor (Top 20 Most Expected Q&A with Full Solutions)
Description: Photoelectric effect, de Broglie, Bohr model, nuclei, radioactivity, diodes, zener, logic gates, communication—Top 20 solved questions.
Q81) Einstein photoelectric equation।
Solution:
Kmax=hν−ϕ,eV0=Kmax
Q82) Threshold frequency ν0।
Solution:
ϕ=hν0⇒ν0=hϕ
Q83) Photoelectric effect में intensity vs frequency का effect।
Solution:
-
Frequency ↑ ⇒ Kmax ↑ (यदि ν>ν0)
-
Intensity ↑ ⇒ photoelectrons की संख्या ↑, Kmax नहीं बढ़ता।
Q84) de Broglie wavelength।
Solution:
λ=ph=mvhQ85) Electron accelerated by V की wavelength।
Solution:
eV=21mv2⇒p=2meV⇒λ=2meVhQ86) Bohr quantisation condition।
Solution:
mvr=2πnhQ87) Hydrogen atom energy levels।
Solution:
En=−n213.6 eVQ88) Transition में photon energy।
Solution:
hν=Ei−Ef,λ=Ei−EfhcQ89) Nuclear radius relation।
Solution:
R=R0A1/3,R0≈1.2×10−15mQ90) Mass defect और binding energy।
Solution:
Δm=Zmp+Nmn−Mnucleus BE=Δmc2Q91) Radioactive decay law।
Solution:
N=N0e−λtQ92) Half-life formula।
Solution:
T1/2=λ0.693Q93) Mean life।
Solution:
τ=λ1Q94) p-n junction forward bias में current क्यों बढ़ता?
Solution: Barrier potential कम होता है ⇒ majority carriers आसानी से cross करते हैं ⇒ current बढ़ता है।
Q95) Reverse bias में current क्यों कम?
Solution: Barrier potential बढ़ता है ⇒ केवल minority carriers ⇒ tiny leakage current।
Q96) Zener diode का use।
Solution: Reverse breakdown region में लगभग constant voltage ⇒ Voltage regulator.
Q97) Rectifier क्या है?
Solution: AC को DC में convert करने वाला circuit (diode based).
Q98) Logic gates: AND gate truth statement।
Solution: AND में output 1 तभी जब दोनों input 1 हों।
Y=A⋅B
Q99) Modulation क्यों जरूरी?
Solution:
-
Low freq signal direct भेजने पर antenna बहुत बड़ा चाहिए
-
Noise ज्यादा
-
Proper transmission के लिए carrier wave पर modulation जरूरी
Q100) Band gap का concept (conductor/semiconductor/insulator)।
Solution:
-
Conductor: band gap ~ 0
-
Semiconductor: small gap (~1 eV order)
-
Insulator: large gap
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