CBSE Class 12 Board Exam Physics Flashcards

24 sample cards from the Physics deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. Compare diamagnetic, paramagnetic, and ferromagnetic materials.

   Diamagnetic: weakly repelled, χ small negative (e.g. bismuth). Paramagnetic: weakly attracted, χ small positive (e.g. aluminium). Ferromagnetic: strongly attracted, χ large positive, retain magnetism (e.g. iron).

2. State the relation between magnetic susceptibility χ and relative permeability μ_r.

   μ_r = 1 + χ. Also B = μ₀(H + M) and M = χH, where M is magnetization and H is magnetic intensity.

3. How does susceptibility of paramagnetic materials depend on temperature (Curie's law)?

   χ = C/T (Curie's law): susceptibility is inversely proportional to absolute temperature, where C is the Curie constant.

4. State Faraday's laws of electromagnetic induction.

   An induced EMF is set up when magnetic flux through a circuit changes; its magnitude equals the rate of change of flux: ε = −dΦ/dt (for N turns, ε = −N dΦ/dt).

5. State Lenz's law and its significance.

   The induced current opposes the change in magnetic flux that produces it. The negative sign in Faraday's law reflects this; it is a consequence of conservation of energy.

6. Give the motional EMF induced in a rod moving in a magnetic field.

   ε = Bvl, where B is field, v is the rod's velocity perpendicular to it, and l is the rod's length.

7. Define self-inductance and give the EMF it produces.

   Self-inductance L relates flux to current: Φ = LI. Induced EMF ε = −L(dI/dt). SI unit: henry (H).

8. Define mutual inductance between two coils.

   Mutual inductance M relates flux in one coil to current in the other: Φ₂ = MI₁; induced EMF ε₂ = −M(dI₁/dt). SI unit: henry.

9. What is the energy stored in an inductor?

   U = ½LI², where L is inductance and I is the current through it.

10. Define RMS value of AC and relate it to peak value for a sinusoidal current.

    RMS (root-mean-square) value is the DC equivalent producing the same heating. I_rms = I₀/√2 ≈ 0.707 I₀; similarly V_rms = V₀/√2.

11. Give the inductive and capacitive reactances in an AC circuit.

    Inductive reactance X_L = ωL = 2πfL. Capacitive reactance X_C = 1/ωC = 1/2πfC. Both have units of ohm.

12. Give the impedance of a series LCR circuit and the resonance condition.

    Z = √[R² + (X_L − X_C)²]. Resonance when X_L = X_C, i.e. ω₀ = 1/√(LC); then Z = R is minimum and current is maximum.

13. What is power factor in an AC circuit, and average power?

    Power factor = cosφ = R/Z. Average power P = V_rms·I_rms·cosφ. A pure inductor or capacitor consumes zero average power (wattless current).

14. Explain the working principle of a transformer and the turns-ratio relation.

    It works on mutual induction, transferring AC power between coils. V_s/V_p = N_s/N_p = I_p/I_s (ideal). Step-up increases voltage; step-down decreases it.

15. What is displacement current, as introduced by Maxwell?

    Displacement current I_D = ε₀(dΦ_E/dt), arising from a changing electric field (e.g. between capacitor plates). It makes Ampère's law consistent and completes Maxwell's equations.

16. List the properties of electromagnetic waves.

    They are transverse; E and B are mutually perpendicular and perpendicular to propagation; they travel in vacuum at c = 3×10⁸ m/s; c = 1/√(μ₀ε₀); E₀/B₀ = c; they carry energy and momentum.

17. Arrange the electromagnetic spectrum in order of increasing frequency.

    Radio waves < microwaves < infrared < visible light < ultraviolet < X-rays < gamma rays (frequency increases, wavelength decreases).

18. State the laws of reflection and the mirror formula.

    Angle of incidence = angle of reflection; incident ray, reflected ray, and normal lie in one plane. Mirror formula: 1/f = 1/v + 1/u, with magnification m = −v/u.

19. State Snell's law and define refractive index.

    n₁ sin i = n₂ sin r (Snell's law). Refractive index n = c/v = speed of light in vacuum / speed in the medium = sin i / sin r.

20. What is the condition for total internal reflection and the critical angle?

    Light must travel from a denser to a rarer medium and the angle of incidence must exceed the critical angle C, where sin C = 1/n (n = denser/rarer).

21. Give the lens maker's formula and the lens formula.

    Lens maker's: 1/f = (n−1)(1/R₁ − 1/R₂). Lens formula: 1/f = 1/v − 1/u; power P = 1/f (in dioptres, f in metres).

22. State the conditions and result for sustained interference (Young's double-slit).

    Sources must be coherent (constant phase difference) and of nearly equal amplitude. Fringe width β = λD/d, where D is slit-to-screen distance and d is slit separation.

23. Give Einstein's photoelectric equation and define work function.

    K_max = hν − φ₀, where φ₀ is the work function (minimum energy to eject an electron) and hν is the photon energy. Below the threshold frequency, no emission occurs. de Broglie wavelength: λ = h/p.

24. State Bohr's quantization condition and the energy of the nth orbit of hydrogen.

    Angular momentum is quantized: L = mvr = nh/2π. Energy E_n = −13.6/n² eV; the ground state (n=1) is −13.6 eV. Mass defect Δm relates to binding energy by E = Δm·c².

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