RUHS / State Nursing Entrance 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 law of equipartition of energy and the average KE of a gas molecule.

   Each degree of freedom contributes ½kT of energy per molecule. Average translational KE of a molecule = (3/2)kT, where k is Boltzmann's constant (1.38 × 10⁻²³ J/K).

2. State Coulomb's law of electrostatics.

   The force between two point charges is F = k·q₁q₂/r², directed along the line joining them; like charges repel, unlike attract. k = 1/4πε₀ ≈ 9 × 10⁹ N·m²/C².

3. Define electric field intensity and electric potential.

   Electric field E = force per unit positive test charge (E = F/q₀; units N/C or V/m, a vector). Electric potential V = work done per unit charge to bring it from infinity to that point (units volt = J/C, a scalar).

4. State Gauss's law.

   The total electric flux through a closed surface equals 1/ε₀ times the net charge enclosed: Φ = ∮E·dA = q_enclosed/ε₀.

5. Write the formula for capacitance of a parallel-plate capacitor and energy stored.

   C = ε₀A/d (with dielectric, C = Kε₀A/d). Energy stored U = ½CV² = ½QV = Q²/2C.

6. State Ohm's law and define resistance.

   Ohm's law: at constant temperature, current through a conductor is directly proportional to the voltage across it (V = IR). Resistance R = V/I; SI unit = ohm (Ω).

7. Write the formula for resistance in terms of resistivity, and how resistivity varies with temperature for metals.

   R = ρL/A, where ρ is resistivity, L length, A cross-sectional area. For metals, resistivity increases with temperature: ρ_T = ρ₀(1 + αΔT).

8. Give the formulae for resistors in series and in parallel.

   Series: R_eq = R₁ + R₂ + R₃ + … (same current). Parallel: 1/R_eq = 1/R₁ + 1/R₂ + … (same voltage); R_eq is less than the smallest resistor.

9. State Kirchhoff's two laws for electric circuits.

   Junction (current) law: the sum of currents entering a node equals the sum leaving (conservation of charge). Loop (voltage) law: the algebraic sum of EMFs and potential drops around any closed loop is zero (conservation of energy).

10. State the Biot–Savart law and the right-hand rule for a current-carrying wire.

    Biot–Savart: dB = (μ₀/4π)·(I·dl × r̂)/r², giving the magnetic field due to a current element. Right-hand rule: thumb points along current, curled fingers give the direction of the magnetic field lines.

11. Write the expression for the magnetic force on a current-carrying conductor and on a moving charge.

    On a conductor: F = BIL sinθ. On a moving charge: F = qvB sinθ (Lorentz force F = q(v × B)). The force is maximum when motion/current is perpendicular to B.

12. State Faraday's laws of electromagnetic induction.

    1st: A changing magnetic flux through a circuit induces an EMF. 2nd: The induced EMF equals the negative rate of change of magnetic flux: ε = −dΦ/dt (for N turns, ε = −N·dΦ/dt).

13. State Lenz's law and the principle it conserves.

    The direction of an induced current always opposes the change in magnetic flux producing it. The negative sign in ε = −dΦ/dt expresses it; Lenz's law is a consequence of conservation of energy.

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

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

15. State Snell's law of refraction and define refractive index.

    Snell's law: n₁ sinθ₁ = n₂ sinθ₂ (sinθ₁/sinθ₂ = n₂/n₁ = constant). Refractive index n = speed of light in vacuum / speed in medium = c/v; it measures how much light bends.

16. State the conditions for total internal reflection.

    (1) Light must travel from a denser to a rarer medium; (2) the angle of incidence must exceed the critical angle θ_c, where sinθ_c = 1/n. Used in optical fibres and prisms.

17. Write the lens-maker's formula and define lens power.

    Lens-maker's formula: 1/f = (n − 1)(1/R₁ − 1/R₂). Power P = 1/f (in metres); unit = dioptre (D). Converging (convex) lenses have positive power; diverging (concave) lenses negative.

18. State the conditions for constructive and destructive interference of light.

    Constructive (bright): path difference = nλ (phase difference 2nπ). Destructive (dark): path difference = (n + ½)λ (phase difference odd multiple of π), where n = 0, 1, 2, …

19. In Young's double-slit experiment, what is the formula for fringe width?

    Fringe width β = λD/d, where λ is wavelength, D is slit-to-screen distance, and d is the slit separation. All bright/dark fringes are equally spaced.

20. What is the photoelectric effect, and write Einstein's photoelectric equation.

    Emission of electrons from a metal when light of sufficient frequency falls on it. Einstein's equation: hν = φ + KE_max, i.e., KE_max = hν − hν₀, where φ = work function and ν₀ = threshold frequency.

21. State de Broglie's hypothesis and the wavelength formula.

    Every moving particle has an associated matter wave of wavelength λ = h/p = h/mv, where h is Planck's constant and p is momentum. It expresses the wave–particle dual nature of matter.

22. Distinguish between nuclear fission and nuclear fusion.

    Fission: a heavy nucleus splits into lighter nuclei releasing energy (e.g., U-235). Fusion: light nuclei combine into a heavier nucleus releasing energy (e.g., H → He in the Sun). Both release energy via mass defect (E = mc²).

23. Define half-life and write the radioactive decay law.

    Half-life (T½) is the time for half the nuclei in a sample to decay; T½ = 0.693/λ. Decay law: N = N₀e^(−λt), where λ is the decay constant and N₀ the initial number of nuclei.

24. In a P–N junction diode, distinguish forward and reverse bias.

    Forward bias: p-side to positive terminal; depletion layer narrows, resistance is low, and the diode conducts. Reverse bias: p-side to negative terminal; depletion layer widens, resistance is high, and almost no current flows (only small leakage).

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