IPU CET 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. Define RMS value of AC and relate it to peak value.

   RMS (root-mean-square) value is the DC equivalent producing the same heating. For sinusoidal AC: I(rms) = I₀/√2 and V(rms) = V₀/√2.

2. Define reactance, impedance, and resonance in a series LCR circuit.

   Inductive reactance X(L) = ωL; capacitive X(C) = 1/ωC; impedance Z = sqrt(R^2 + (X(L) − X(C))^2). Resonance occurs at ω = 1/sqrt(LC), where Z is minimum (= R) and current is maximum.

3. Define power factor and average power in an AC circuit.

   Power factor = cosφ = R/Z. Average power P = V(rms) I(rms) cosφ. For a pure inductor or capacitor cosφ = 0, so average power is zero (wattless current).

4. What are electromagnetic waves and their key properties?

   EM waves are mutually perpendicular oscillating electric and magnetic fields propagating perpendicular to both; they are transverse, need no medium, travel at c = 1/sqrt(μ₀ε₀) = 3×10^8 m/s in vacuum, and carry energy/momentum.

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

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

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

   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, with magnification m = −v/u.

7. State Snell's law and the lens maker's formula.

   Snell's law: n₁ sinθ₁ = n₂ sinθ₂ (refractive index n = c/v). Lens maker's: 1/f = (n−1)(1/R₁ − 1/R₂), with lens formula 1/v − 1/u = 1/f.

8. Define critical angle and 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). Beyond C, light is totally internally reflected; used in optical fibres and prisms.

9. Define power of a lens and combination of thin lenses in contact.

   Power P = 1/f (in dioptres, f in metres); converging lens has positive P. For lenses in contact: P = P₁ + P₂ + ... .

10. State Huygens' principle and the condition for constructive/destructive interference.

    Every point on a wavefront acts as a source of secondary wavelets; their envelope gives the new wavefront. Constructive: path difference = nλ; destructive: (n + 1/2)λ.

11. Give the fringe width in Young's double-slit experiment.

    β = λD/d, where D is slit-to-screen distance and d is slit separation; fringe width is the same for bright and dark fringes.

12. Distinguish interference and diffraction, and state Brewster's law for polarization.

    Interference is superposition from two coherent sources (uniform fringes); diffraction is bending around obstacles (central maximum brightest, decreasing intensity). Brewster's law: at polarizing angle i(p), tan i(p) = n, and reflected light is fully polarized.

13. State the photoelectric equation and define work function.

    Einstein's equation: hν = φ₀ + (1/2)mv(max)^2, i.e. KE(max) = hν − φ₀. Work function φ₀ is the minimum energy needed to eject an electron; the threshold frequency is ν₀ = φ₀/h.

14. State the de Broglie hypothesis and the wavelength formula.

    Matter has wave nature; the wavelength of a particle is λ = h/p = h/mv. For an electron accelerated through V volts, λ ≈ 12.27/√V Å.

15. State the Bohr postulates for the hydrogen atom.

    Electrons orbit in stationary states without radiating; angular momentum is quantized (mvr = nh/2π); energy is emitted/absorbed only on transitions, with hν = E₂ − E₁.

16. Give the radius and energy of the nth Bohr orbit and the energy of the ground state.

    r(n) ∝ n^2 (= 0.53 n^2 Å); E(n) = −13.6/n^2 eV; ground state (n=1) energy = −13.6 eV. Energy increases (becomes less negative) with n.

17. Define mass defect, binding energy, and nuclear density.

    Mass defect Δm = (sum of nucleon masses) − (nuclear mass); binding energy = Δm·c^2. Nuclear density is nearly constant (~2.3×10^17 kg/m^3) since R = R₀A^(1/3).

18. Distinguish alpha, beta, and gamma decay.

    Alpha: emission of a helium nucleus (A−4, Z−2). Beta-minus: a neutron becomes a proton emitting an electron (Z+1, A same). Gamma: emission of high-energy photons with no change in A or Z.

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

    N = N₀ e^(−λt); activity decreases exponentially. Half-life T(1/2) = 0.693/λ is the time for half the nuclei to decay; mean life τ = 1/λ.

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

    Intrinsic: pure, equal electrons and holes. n-type: doped with pentavalent atoms, electrons majority. p-type: doped with trivalent atoms, holes majority. Doping greatly increases conductivity.

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

    Forward bias (p to +): depletion layer narrows, current flows easily. Reverse bias: depletion layer widens, only tiny leakage current flows. The diode thus acts as a one-way valve (rectifier).

22. Compare half-wave and full-wave rectifiers.

    A half-wave rectifier uses one diode and conducts during one half-cycle (low efficiency, ripple frequency = supply f). A full-wave rectifier (two diodes/bridge) conducts both half-cycles (ripple frequency = 2× supply f, higher efficiency).

23. What is the use of a Zener diode and a light-emitting diode (LED)?

    A Zener diode operates in reverse breakdown at a fixed voltage and is used as a voltage regulator. An LED is a forward-biased diode that emits light when electrons and holes recombine.

24. What is the principle of dimensions used to convert units between systems?

    Using n₁u₁ = n₂u₂ with u expressed in [M^a L^b T^c]; the numerical value changes inversely with the size of the chosen units, keeping the physical quantity unchanged.

What this deck covers

Physics flashcards FAQ