BITSAT 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. State the resonance condition for a series LCR circuit and define power factor.

   Resonance when X_L = X_C, i.e. f = 1/(2π√(LC)); impedance is minimum (=R) and current maximum. Power factor = cosφ = R/Z; average power P = V_rms I_rms cosφ.

2. What are rms and peak values of AC, and the transformer relation?

   V_rms = V₀/√2, I_rms = I₀/√2. Ideal transformer: V_s/V_p = N_s/N_p = I_p/I_s (step-up/step-down).

3. State the properties of electromagnetic waves and give the speed of light relation.

   EM waves are transverse, with E ⊥ B ⊥ direction of propagation, travel in vacuum at c = 1/√(μ₀ε₀) ≈ 3×10⁸ m/s. They carry energy and momentum; E₀/B₀ = c.

4. List the EM spectrum in order of increasing frequency.

   Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays (increasing frequency, decreasing wavelength).

5. State the laws of reflection and the mirror formula with magnification.

   Angle of incidence = angle of reflection, in the same plane. Mirror formula: 1/v + 1/u = 1/f; magnification m = −v/u = h'/h.

6. State Snell's law and define the critical angle for total internal reflection.

   n₁ sinθ₁ = n₂ sinθ₂. Critical angle: sinθ_c = 1/n (light going from denser to rarer); beyond θ_c total internal reflection occurs.

7. Give the lens maker's formula and the lens formula with power.

   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, f in metres); combined power P = P₁ + P₂.

8. Explain dispersion through a prism and angular dispersion.

   A prism splits white light into colours because refractive index varies with wavelength (violet bends most, red least). Deviation δ = (n−1)A for a thin prism; angular dispersion = (n_v − n_r)A.

9. State the conditions for constructive and destructive interference (Young's double slit).

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

10. Give the condition for minima in single-slit diffraction.

    Minima occur when a sinθ = nλ (n = 1,2,3...), where a is slit width. The central maximum is twice as wide as other maxima.

11. State Malus's law and Brewster's law for polarization.

    Malus's law: transmitted intensity I = I₀ cos²θ through a polarizer. Brewster's law: at the polarizing angle, tanθ_p = n, and reflected and refracted rays are perpendicular.

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

    K_max = hν − φ₀, where φ₀ = hν₀ is the work function (minimum energy to eject an electron) and ν₀ the threshold frequency. Below ν₀ no emission occurs regardless of intensity.

13. Give the de Broglie wavelength of a particle and that of an electron accelerated through V volts.

    λ = h/p = h/mv. For an electron accelerated through potential V: λ = 12.27/√V Å (with V in volts).

14. State Bohr's postulates and give the radius and energy of the nth orbit in hydrogen.

    Electrons occupy stationary orbits with quantized angular momentum L = nh/2π; energy is emitted/absorbed on transitions (E = hν). Radius r_n = 0.53 n² Å; energy E_n = −13.6/n² eV.

15. 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 (UV, n₁=1), Balmer (visible, n₁=2), Paschen, Brackett, Pfund (IR).

16. Define mass defect and binding energy, and the energy equivalent of 1 amu.

    Mass defect Δm = (sum of nucleon masses) − (nuclear mass); binding energy = Δm c². 1 amu = 931.5 MeV. Higher binding energy per nucleon means a more stable nucleus (peak near iron, A≈56).

17. State the law of radioactive decay and define half-life and mean life.

    N = N₀e^(−λt); activity A = λN. Half-life T½ = 0.693/λ; mean life τ = 1/λ = T½/0.693. Half-life is the time for half the nuclei to decay.

18. Distinguish alpha, beta, and gamma radiation.

    Alpha: helium nucleus (⁴₂He), low penetration, high ionization; Beta: electron/positron, moderate penetration; Gamma: high-energy photon, highest penetration, no charge/mass change.

19. Distinguish nuclear fission and fusion.

    Fission: a heavy nucleus splits into lighter nuclei releasing energy (e.g., U-235); Fusion: light nuclei combine into a heavier one (e.g., hydrogen to helium in the Sun), releasing even more energy per nucleon.

20. Distinguish intrinsic and extrinsic (n-type, p-type) semiconductors.

    Intrinsic: pure semiconductor with equal electrons and holes. Extrinsic: doped — n-type (pentavalent donor, majority electrons), p-type (trivalent acceptor, majority holes).

21. Describe a p-n junction and forward vs reverse bias.

    A p-n junction has a depletion region with a built-in potential barrier. Forward bias (p to +) lowers the barrier and conducts; reverse bias widens the depletion region and blocks current (allows only small leakage).

22. What is a rectifier, and how do half-wave and full-wave rectifiers differ?

    A rectifier converts AC to DC using diodes. A half-wave rectifier uses one diode and conducts in one half-cycle (output frequency = input). A full-wave rectifier (two diodes/bridge) uses both half-cycles (output frequency = 2× input), giving more efficient DC.

23. What is a Zener diode and its main application?

    A heavily doped diode operated in reverse breakdown at a sharp Zener voltage; the voltage stays constant over a range of currents, so it is used as a voltage regulator.

24. Give the logic outputs of AND, OR, and NOT gates and name the universal gates.

    AND: output 1 only if all inputs 1; OR: output 1 if any input 1; NOT: inverts input. NAND and NOR are universal gates (any logic circuit can be built from them).

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