KCET 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. What is the force on a charge and on a current-carrying wire in a magnetic field?

   On a charge: F = qv × B (magnitude qvB sinθ). On a wire: F = IL × B (magnitude BIL sinθ). The Lorentz force is F = q(E + v × B).

2. State Faraday's law and Lenz's law of electromagnetic induction.

   Faraday's law: induced EMF ε = −dΦ/dt (Φ = magnetic flux). Lenz's law: the induced current opposes the change in flux producing it (the negative sign), conserving energy.

3. Define self-inductance and mutual inductance, and the energy stored in an inductor.

   Self: ε = −L dI/dt. Mutual: ε₂ = −M dI₁/dt. Energy stored in an inductor U = ½LI².

4. For an AC circuit, give the reactances of an inductor and capacitor and the resonance frequency of an LCR circuit.

   Inductive reactance X_L = ωL; capacitive reactance X_C = 1/ωC. Resonance when X_L = X_C, at f = 1/(2π√(LC)), where impedance is minimum.

5. Define RMS value of AC and power factor.

   I_rms = I₀/√2, V_rms = V₀/√2. Average power P = V_rms·I_rms·cosφ, where cosφ = R/Z is the power factor (φ = phase difference).

6. List the electromagnetic spectrum in order of increasing frequency.

   Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays (increasing frequency, decreasing wavelength). All travel at c = 3 × 10⁸ m/s in vacuum.

7. What did Maxwell add to Ampere's law, and what is the speed of EM waves?

   Maxwell added displacement current (I_d = ε₀ dΦ_E/dt) to account for changing electric fields. EM wave speed c = 1/√(μ₀ε₀); E and B are perpendicular to each other and to propagation.

8. State the laws of reflection and the mirror formula with sign convention.

   Angle of incidence = angle of reflection. Mirror formula: 1/v + 1/u = 1/f, with f = R/2; distances measured from the pole, with the Cartesian sign convention.

9. State Snell's law, the lens maker's formula, and the lens formula.

   Snell's law: n₁ sinθ₁ = n₂ sinθ₂. Lens maker's: 1/f = (n − 1)(1/R₁ − 1/R₂). Lens formula: 1/v − 1/u = 1/f; power P = 1/f (in dioptres).

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

    Critical angle θ_c = sin⁻¹(1/n) for light going from denser to rarer medium. TIR occurs when the angle of incidence exceeds θ_c (used in optical fibres).

11. Give the magnifying power of a simple microscope, compound microscope, and telescope.

    Simple microscope: M = 1 + D/f. Compound microscope: M = (L/f_o)(D/f_e). Astronomical telescope (normal adjustment): M = f_o/f_e, length = f_o + f_e.

12. State the conditions for constructive and destructive interference in Young's double-slit experiment.

    Constructive (bright): path difference = nλ. Destructive (dark): path difference = (n + ½)λ. Fringe width β = λD/d.

13. State Huygens' principle and the condition for the first minimum in single-slit diffraction.

    Huygens' principle: every point on a wavefront acts as a source of secondary wavelets; their envelope forms the new wavefront. First diffraction minimum: a sinθ = λ (a = slit width).

14. What is polarisation and Brewster's law?

    Polarisation restricts light vibrations to one plane (transverse-wave evidence). Brewster's law: at the polarising angle θ_p, tanθ_p = n, and the reflected ray is fully polarised, perpendicular to the refracted ray.

15. State Einstein's photoelectric equation and define work function and threshold frequency.

    K_max = hν − φ₀, where φ₀ = work function = hν₀ (minimum energy to eject an electron), ν₀ = threshold frequency. Photon energy E = hν; h = 6.63 × 10⁻³⁴ J·s.

16. State the de Broglie wavelength formula for a particle.

    λ = h/p = h/mv = h/√(2mKE). For an electron accelerated through V volts: λ ≈ 1.227/√V nm.

17. State Bohr's postulates for the hydrogen atom and the energy of the nth orbit.

    Electrons occupy stationary orbits where L = nℏ (angular momentum quantised); radiation occurs only on transitions (hν = E₂ − E₁). Energy E_n = −13.6/n² eV; radius r_n ∝ n².

18. Give the Rydberg formula for hydrogen spectral lines and name the series.

    1/λ = R(1/n₁² − 1/n₂²), R = 1.097 × 10⁷ m⁻¹. Series: Lyman (n₁=1, UV), Balmer (n₁=2, visible), Paschen/Brackett/Pfund (n₁=3,4,5, IR).

19. Define mass defect, binding energy, and the relation E = mc².

    Mass defect Δm = (sum of nucleon masses) − (nuclear mass). Binding energy = Δm·c²; 1 u ≈ 931.5 MeV. Higher binding energy per nucleon means a more stable nucleus (peak near iron).

20. State the radioactive decay law and define half-life.

    N = N₀e^(−λt), λ = decay constant. Half-life T₁/₂ = ln2/λ = 0.693/λ; mean life τ = 1/λ. Activity A = λN.

21. Compare alpha, beta, and gamma radiation.

    Alpha (He nucleus): +2 charge, least penetrating, most ionising. Beta (electron/positron): ±1 charge, moderate penetration. Gamma (photon): no charge, most penetrating, least ionising.

22. Compare intrinsic, n-type, and p-type semiconductors.

    Intrinsic: pure, n_e = n_h. n-type: doped with pentavalent (donor) impurity, majority carriers are electrons. p-type: doped with trivalent (acceptor) impurity, majority carriers are holes.

23. How does a p-n junction diode behave under forward and reverse bias?

    Forward bias (p to +): depletion region narrows, low resistance, current flows easily after the barrier voltage (~0.7 V for Si). Reverse bias: depletion widens, high resistance, only tiny leakage current until breakdown.

24. Distinguish half-wave from full-wave rectification, and name the diode used as a voltage regulator.

    Half-wave rectifier conducts during one half-cycle (uses 1 diode); full-wave conducts during both half-cycles (uses 2 diodes or a bridge of 4). A Zener diode (operated in reverse breakdown) acts as a voltage regulator.

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