CBSE Class 12 Physics 2026: Top 100 High-Yield Questions (Full Solutions/Steps) – Board Score Booster Set

 UNIT-1: Electrostatics (Q1–Q10)

1) Coulomb’s Law likho aur vector form बताओ।

Force line joining charges ke along hota hai; like charges repel, unlike attract.

2) Electric field due to point charge निकालो।

3) Dipole ka electric field on axial line?

Solution (main steps): Dipole moment $p=q(2a)$.
Axial point distance $r\gg a$:

Direction: dipole moment ke along (from − to +).

4) Dipole ka field on equatorial line?

Direction: $\vec p$ ke opposite.

5) Gauss law statement + formula.

Solution:
Closed surface se total flux:

6) Infinite plane sheet (surface charge density $\sigma$) ka E-field?

Solution: Using Gauss (pillbox):

Two sides par equal magnitude.

7) Infinite line charge (linear density $\lambda$) ka E-field at distance r?

Solution: Cylindrical Gaussian surface:

$$E(2\pi rL)=\frac{\lambda L}{\varepsilon_0}\Rightarrow E=\frac{\lambda}{2\pi\varepsilon_0 r}$$

8) Conducting sphere (charge Q, radius R) ka potential outside/inside?

Solution:
Outside $(r\ge R)$:

$$V=\frac{1}{4\pi\varepsilon_0}\frac{Q}{r}$$

Inside conductor $(r\le R)$: constant

$$V=\frac{1}{4\pi\varepsilon_0}\frac{Q}{R}$$

9) Capacitance of parallel plate capacitor (air) and with dielectric k.

Solution:

$$C=\frac{\varepsilon_0A}{d},\qquad C'=\frac{k\varepsilon_0A}{d}=kC$$

10) Energy stored in capacitor derive.

Solution:

✅ UNIT-2: Current Electricity (Q11–Q20)

11) Ohm’s law + V–I graph.

Solution: $V=IR$. V–I straight line, slope = R.

12) Resistivity ρ definition + relation with R.

Solution:

$$R=\rho\frac{L}{A},\quad \rho=\frac{RA}{L}$$

Unit: $\Omega\,m$

13) Temperature dependence: $R=R_0(1+\alpha \Delta T)$ meaning.

Solution: $\alpha$=temperature coefficient. Metals: $\alpha>0$.

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14) Series–parallel resistors equivalent.

Solution:
Series: $R_s=R_1+R_2+\cdots$
Parallel: $\frac1{R_p}=\frac1{R_1}+\frac1{R_2}+\cdots$

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15) Kirchhoff’s laws लिखो।

Solution:
Junction: $\sum I=0$
Loop: $\sum \Delta V=0$

16) Wheatstone bridge balanced condition.

Solution:

$$\frac{P}{Q}=\frac{R}{S}$$

Galvanometer current zero.

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17) Meter bridge formula (unknown X, known R).

Solution: Balance length $l$:

$$\frac{X}{R}=\frac{l}{100-l} \Rightarrow X=R\frac{l}{100-l}$$

18) Potentiometer principle + emf comparison.

Solution: Potential gradient $k=V/L$.

$$\frac{E_1}{E_2}=\frac{l_1}{l_2}$$

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19) Drift velocity and current relation.

Solution:

$$I=nAe v_d$$

Current density $J=ne v_d$.

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20) Power in resistor.

Solution:

✅ UNIT-3: Moving Charges & Magnetism (Q21–Q30)

21) Lorentz force formula.

Solution:

$$\vec F=q(\vec E+\vec v\times \vec B)$$

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22) Force on current-carrying conductor.

Solution:

$$\vec F=I(\vec L\times \vec B),\quad F=BIL\sin\theta$$

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23) Magnetic field at center of circular loop (N turns, radius R).

Solution:

24) Long straight wire field at distance r.

Solution:

$$B=\frac{\mu_0 I}{2\pi r}$$

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25) Solenoid field inside (turn density n).

Solution:

$$B=\mu_0 n I$$

(air core)

26) Cyclotron: frequency & maximum energy idea.

Solution:

$$f=\frac{qB}{2\pi m}$$

(Max speed when radius hits max $r$: $v=\frac{qBr}{m}$)

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27) Torque on magnetic dipole in uniform B.

Solution:

$$\vec \tau=\vec m\times \vec B,\quad \tau=mB\sin\theta$$

28) Moving charge in uniform B—circular motion radius.

Solution:

$$qvB=\frac{mv^2}{r}\Rightarrow r=\frac{mv}{qB}$$

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29) Biot–Savart law statement.

Solution:

$$d\vec B=\frac{\mu_0}{4\pi}\frac{I\,d\vec l\times \hat r}{r^2}$$

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30) Ampere’s circuital law.

Solution:

✅ UNIT-4: Magnetism & Matter (Q31–Q40)

31) Magnetic susceptibility χ, relation with M and H.

Solution:

$$\vec M=\chi \vec H$$

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32) Relation between B, H, M.

Solution:

33) Dia/Para/Ferro ka behavior?

Solution:
Diamagnetic: $\chi<0$, weakly repelled.
Paramagnetic: $\chi>0$, weakly attracted.
Ferromagnetic: very large $\chi$, strongly attracted, domains.

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34) Earth’s magnetic elements: declination, dip, horizontal component.

Solution:
Declination: geographic N vs magnetic N angle.
Dip: B with horizontal angle.
$B_H=B\cos I$.

35) Tangent law (deflection magnetometer).

Solution:

$$\tan\theta=\frac{B}{B_H}$$

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36) Bar magnet as dipole: axial field formula.

Solution:

$$B_\text{axial}=\frac{\mu_0}{4\pi}\frac{2m}{r^3}$$

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37) Equatorial field of bar magnet.

Solution:

$$B_\text{eq}=\frac{\mu_0}{4\pi}\frac{m}{r^3}$$

38) Hysteresis loop significance.

Solution: Retentivity, coercivity, energy loss (area).

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39) Soft iron vs steel (use).

Solution: Soft iron: low coercivity—electromagnets.
Steel: high retentivity—permanent magnets.

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40) Magnetic moment of current loop.

Solution:

✅ UNIT-5: EMI (Q41–Q50)

41) Faraday’s laws.

Solution:
Induced emf proportional to rate of change of flux:

$$\varepsilon=-\frac{d\Phi}{dt}$$

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42) Lenz’s law meaning.

Solution: Induced current change ko oppose karta hai (minus sign).

43) Self-inductance L definition.

Solution:

$$\Phi=LI,\quad \varepsilon=-L\frac{dI}{dt}$$

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44) Energy in inductor.

Solution:

$$U=\frac12 LI^2$$

45) Motional emf in rod length l moving with v in B.

Solution:

$$\varepsilon=Blv$$

(when v ⟂ B and rod ⟂ v)

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46) Eddy currents—uses & losses.

Solution: Uses: braking, induction furnace. Loss: heating; reduce by laminations.

47) Transformer: relation between voltages.

Solution:

$$\frac{V_s}{V_p}=\frac{N_s}{N_p}$$

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48) Transformer power (ideal).

Solution:

$$V_pI_p=V_sI_s$$

49) AC generator principle.

Solution: Rotating coil, changing flux ⇒ $\varepsilon=\varepsilon_0\sin\omega t$.

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50) Fleming’s right-hand rule use.

Solution: Generator direction (induced current).

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✅ UNIT-6: AC (Q51–Q60)

51) RMS value of AC current.

Solution:

$$I_\text{rms}=\frac{I_0}{\sqrt2},\quad V_\text{rms}=\frac{V_0}{\sqrt2}$$

52) Reactance of inductor/capacitor.

Solution:

$$X_L=\omega L,\quad X_C=\frac1{\omega C}$$

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53) Impedance of series RLC.

Solution:

$$Z=\sqrt{R^2+(X_L-X_C)^2}$$

54) Resonance condition.

Solution:

$$X_L=X_C\Rightarrow \omega_0=\frac1{\sqrt{LC}}$$

55) Power factor.

Solution:

$$\cos\phi=\frac{R}{Z}$$

Power: $P=V_\text{rms}I_\text{rms}\cos\phi$

P=Vrms​Irms​cosϕ

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66) Mirror formula.

Solution:

$$\frac1f=\frac1v+\frac1u$$

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67) Lens formula.

Solution:

$$\frac1f=\frac1v-\frac1u$$

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68) Magnification (lens).

Solution:

$$m=\frac{h'}{h}=\frac{v}{u}$$

69) Power of lens.

Solution:

$$P=\frac1f(\text{in meter}),\ \text{unit: diopter}$$

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70) Lens maker formula.

Solution:

$$\frac1f=(\mu-1)\left(\frac1{R_1}-\frac1{R_2}\right)$$

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71) Total internal reflection conditions.

Solution:

1. denser → rarer

2. incidence angle > critical angle

$$\sin C=\frac{n_2}{n_1}$$

72) Optical fiber working.

Solution: Repeated TIR, light guided.

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73) Refraction at spherical surface formula.

Solution:

$$\frac{n_2}{v}-\frac{n_1}{u}=\frac{n_2-n_1}{R}$$

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74) Prism deviation at minimum deviation.

Solution (main):

$$n=\frac{\sin\left(\frac{A+D_m}{2}\right)}{\sin\left(\frac{A}{2}\right)}$$

75) Combination of lenses in contact.

Solution:

$$\frac1F=\frac1{f_1}+\frac1{f_2}\Rightarrow P=P_1+P_2$$

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✅ UNIT-9: Wave Optics (Q76–Q85)

76) Young’s double slit fringe width.

Solution:

$$\beta=\frac{\lambda D}{d}$$

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77) Conditions for bright/dark fringes.

Solution:
Bright: $\Delta=n\lambda$
Dark: $\Delta=(2n+1)\frac{\lambda}{2}$

78) Diffraction vs interference (1 line difference).

Solution: Diffraction: single slit/aperture; interference: two coherent sources.

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79) Single slit diffraction: angular width of central maxima.

Solution:
Minima: $a\sin\theta=m\lambda$.
Central max width $\approx \frac{2\lambda}{a}$ (in radians small angle)

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80) Polarisation proves transverse nature.

Solution: Only transverse waves polarise; light polarises ⇒ transverse.

81) Brewster law.

Solution:

$$\tan i_B=n$$

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82) Malus law.

Solution:

$$I=I_0\cos^2\theta$$

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83) Rayleigh scattering—blue sky.

Solution: Scattering $\propto \frac1{\lambda^4}$ ⇒ blue more scattered.

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84) Doppler effect in light? (basic)

Solution: Frequency shift due to relative motion; used in astronomy.

85) Coherent sources condition.

Solution: Same frequency, constant phase difference.

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✅ UNIT-10: Dual Nature (Q86–Q90)

86) Photoelectric equation.

Solution:

$$K_\text{max}=h\nu-\phi$$

Stopping potential: $eV_0=K_\text{max}$

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87) Threshold frequency.

Solution:

$$\phi=h\nu_0 \Rightarrow \nu_0=\frac{\phi}{h}$$

88) de Broglie wavelength.

Solution:

$$\lambda=\frac{h}{p}=\frac{h}{mv}$$

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89) Electron accelerated by V: wavelength.

Solution:

$$eV=\frac12mv^2 \Rightarrow p=\sqrt{2meV} \Rightarrow \lambda=\frac{h}{\sqrt{2meV}}$$

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90) Davisson–Germer experiment conclusion.

Solution: Electron diffraction observed ⇒ matter waves exist.

✅ UNIT-11: Atoms & Nuclei (Q91–Q97)

91) Bohr’s angular momentum quantisation.

Solution:

$$mvr=\frac{nh}{2\pi}$$

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92) Hydrogen energy levels.

Solution:

$$E_n=-\frac{13.6}{n^2}\ \text{eV}$$

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93) Radius of nth orbit.

Solution:

$$r_n=a_0 n^2,\ a_0=0.529\ \text{Å}$$

94) Nuclear radius relation.

Solution:

$$R=R_0 A^{1/3},\ R_0\approx 1.2\times 10^{-15}\text{ m}$$

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95) Binding energy definition.

Solution: Mass defect $\Delta m$:

$$B.E=\Delta m\,c^2$$

Per nucleon stability indicator.

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96) Radioactive decay law.

Solution:

97) Half-life formula.

Solution:

$$T_{1/2}=\frac{\ln 2}{\lambda}=0.693/\lambda$$

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✅ UNIT-12: Semiconductors + Communication (Q98–Q100)

98) p-n junction forward vs reverse bias.

Solution: Forward bias barrier कम ⇒ current flows. Reverse bias barrier बढ़ ⇒ tiny leakage.

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99) Zener diode use.

Solution: Reverse breakdown me constant voltage देता ⇒ voltage regulator.

100) Modulation क्यों जरूरी? AM basics.

Solution: Low-freq signal direct transmit नहीं (antenna huge, noise). Carrier wave पर modulation. AM: carrier amplitude varies with signal.