NEET / State Class 12 Board (e.g. ISC) 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. How does a moving coil galvanometer work, and what is current sensitivity?

   A current-carrying coil in a radial magnetic field experiences a torque proportional to current, deflecting against a spring. Current sensitivity = deflection per unit current = NAB/k.

2. How is a galvanometer converted into an ammeter and into a voltmeter?

   Ammeter: connect a low resistance (shunt) in parallel. Voltmeter: connect a high resistance in series with the galvanometer.

3. Define magnetic dipole moment of a current loop.

   m = NIA, where N is number of turns, I the current, and A the loop area. It is a vector perpendicular to the plane of the loop. SI unit: A·m².

4. Compare diamagnetic, paramagnetic, and ferromagnetic materials.

   Diamagnetic: weakly repelled, susceptibility small and negative. Paramagnetic: weakly attracted, small positive susceptibility. Ferromagnetic: strongly attracted, large positive susceptibility, shows hysteresis and retains magnetism.

5. Define magnetic susceptibility and relative permeability, and relate them.

   Susceptibility χ = M/H (ratio of magnetisation to magnetising field). Relative permeability μ_r = 1 + χ; also B = μ₀(H + M).

6. What is the Curie law for paramagnetic materials?

   Magnetisation is directly proportional to applied field and inversely proportional to absolute temperature: M = C(B/T), where C is Curie's constant.

7. State Faraday's laws of electromagnetic induction.

   First law: an EMF is induced when magnetic flux linked with a circuit changes. Second law: the magnitude of induced EMF equals the rate of change of flux, ε = −dΦ/dt.

8. State Lenz's law and what conservation principle it expresses.

   The induced current opposes the change in magnetic flux that produces it (hence the minus sign in Faraday's law). It is a consequence of conservation of energy.

9. Define self-inductance and give the EMF expression.

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

10. What is mutual inductance?

    Mutual inductance M relates the EMF induced in one coil to the rate of change of current in a neighbouring coil: ε₂ = −M(dI₁/dt). SI unit: henry (H).

11. What is the RMS value of an alternating current and its relation to peak value?

    RMS (root-mean-square) is the equivalent DC value producing the same heating effect. For sinusoidal AC, I_rms = I₀/√2 ≈ 0.707 I₀.

12. Define inductive reactance and capacitive reactance.

    Inductive reactance X_L = ωL = 2πfL. Capacitive reactance X_C = 1/(ωC) = 1/(2πfC). Both measured in ohms.

13. Give the impedance of a series LCR circuit.

    Z = √(R² + (X_L − X_C)²), where X_L = ωL and X_C = 1/ωC.

14. State the condition for resonance in a series LCR circuit and the resonant frequency.

    Resonance occurs when X_L = X_C, giving minimum impedance Z = R. Resonant frequency f₀ = 1/(2π√(LC)).

15. Define power factor in an AC circuit.

    Power factor = cosφ = R/Z, the ratio of true power to apparent power. Average power P = V_rms·I_rms·cosφ.

16. What is the order of frequency and wavelength arrangement of the electromagnetic spectrum?

    In order of increasing frequency (decreasing wavelength): radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays.

17. What is displacement current and which equation introduced it?

    Displacement current I_d = ε₀(dΦ_E/dt) arises from a changing electric field. Maxwell added it to Ampère's law to make it consistent for charging capacitors.

18. Give the speed of electromagnetic waves in vacuum in terms of ε₀ and μ₀.

    c = 1/√(μ₀ε₀) ≈ 3×10⁸ m/s. EM waves are transverse with E and B perpendicular to each other and to the direction of propagation.

19. State the laws of reflection and Snell's law of refraction.

    Reflection: angle of incidence equals angle of reflection; incident ray, reflected ray and normal lie in one plane. Snell's law: n₁sini = n₂sinr, or refractive index n = sini/sinr.

20. Give the mirror formula and the lens formula.

    Mirror: 1/v + 1/u = 1/f. Lens: 1/v − 1/u = 1/f. Magnification: mirror m = −v/u; lens m = v/u.

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

    Critical angle C is the angle of incidence in the denser medium for which the refraction angle is 90°; sinC = 1/n. TIR occurs when light travels from a denser to a rarer medium and the incidence angle exceeds C.

22. State the lensmaker's formula.

    1/f = (n − 1)(1/R₁ − 1/R₂), where n is refractive index of the lens material and R₁, R₂ are the radii of curvature of the two surfaces.

23. State Young's double slit fringe width formula and the condition for bright fringes.

    Fringe width β = λD/d, where D is slit-to-screen distance and d the slit separation. Bright fringes (constructive): path difference = nλ; dark fringes: (n+½)λ.

24. What does the photoelectric effect's Einstein equation state, and what is the work function?

    E = hν = φ + K_max, i.e., hν = φ + ½mv²_max. Work function φ is the minimum energy needed to eject an electron from the metal surface; threshold frequency ν₀ = φ/h.

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