Q1. A 2 kg body accelerates at 3 m/s². What net force acts on it?
A. 6 NB. 1.5 NC. 5 ND. 9 NCorrect: A. 6 N
Explanation: F = ma = 2 × 3 = 6 N.
Key Concept / Clinical Relevance: Newton’s second law
⚛️ Physics MCQs
100 questions • Q1–50 Moderate • Q51–100 Very Difficult • 30 Clinical/Scenario-based • Tap “Answer” for explanation.
Q2. A car increases its speed from 10 to 20 m/s in 5 s. Its average acceleration is:
A. 1 m/s²B. 2 m/s²C. 5 m/s²D. 6 m/s²Correct: B. 2 m/s²
Explanation: a = Δv/Δt = 10/5 = 2 m/s².
Key Concept / Clinical Relevance: Kinematics
Q3. Which quantity is conserved in an isolated collision even when kinetic energy is not?
A. VelocityB. ForceC. MomentumD. AccelerationCorrect: C. Momentum
Explanation: Total linear momentum is conserved in every isolated collision.
Key Concept / Clinical Relevance: Conservation of momentum
Q4. A 10 N force moves an object 4 m in its own direction. Work done is:
A. 2.5 JB. 14 JC. 400 JD. 40 JCorrect: D. 40 J
Explanation: W = Fs cos 0° = 10 × 4 = 40 J.
Key Concept / Clinical Relevance: Work
Q5. If the speed of a body doubles, its kinetic energy becomes:
A. 4 timesB. 2 timesC. 8 timesD. unchangedCorrect: A. 4 times
Explanation: Kinetic energy is proportional to v².
Key Concept / Clinical Relevance: Kinetic energy
Q6. For uniform circular motion, centripetal acceleration is directed:
A. TangentiallyB. Toward centreC. Away from centreD. Along velocityCorrect: B. Toward centre
Explanation: Centripetal acceleration v²/r always points toward the centre.
Key Concept / Clinical Relevance: Circular motion
Q7. The pressure at depth h in a static liquid of density ρ, above atmospheric contribution, is:
A. ρg/hB. gh/ρC. ρghD. ρh/gCorrect: C. ρgh
Explanation: Hydrostatic gauge pressure is ρgh.
Key Concept / Clinical Relevance: Fluid statics
Q8. A patient receives IV fluid from a bag raised higher above the vein. Why does flow tend to increase?
A. Fluid density fallsB. Viscosity becomes zeroC. Venous pressure must riseD. Hydrostatic pressure head increasesCorrect: D. Hydrostatic pressure head increases
Explanation: Raising the bag increases ΔP = ρgh and therefore the driving pressure for flow.
Key Concept / Clinical Relevance: Hydrostatic pressure in IV infusion
Q9. According to Poiseuille’s law, flow through a cylindrical tube is most sensitive to changes in:
A. RadiusB. LengthC. Pressure onlyD. DensityCorrect: A. Radius
Explanation: Laminar flow varies with the fourth power of radius.
Key Concept / Clinical Relevance: Poiseuille flow
Q10. Reynolds number is most useful for estimating the tendency toward:
A. Radioactive decayB. Turbulent flowC. RefractionD. Heat radiationCorrect: B. Turbulent flow
Explanation: Higher Reynolds number increases the likelihood of turbulence.
Key Concept / Clinical Relevance: Fluid dynamics
Q11. Surface tension tends to make a liquid surface:
A. Maximise areaB. Increase volume indefinitelyC. Minimise areaD. Eliminate pressureCorrect: C. Minimise area
Explanation: Surface tension minimizes surface area.
Key Concept / Clinical Relevance: Surface tension
Q12. Young’s modulus is the ratio of:
A. Strain/stressB. Force/area onlyC. Energy/timeD. Stress/strainCorrect: D. Stress/strain
Explanation: Within the elastic limit, Young’s modulus = longitudinal stress/strain.
Key Concept / Clinical Relevance: Elasticity
Q13. Heat transfer through direct molecular interaction in a stationary solid is mainly:
A. ConductionB. ConvectionC. RadiationD. EvaporationCorrect: A. Conduction
Explanation: Conduction transfers thermal energy through microscopic interactions without bulk flow.
Key Concept / Clinical Relevance: Heat transfer
Q14. A febrile patient loses heat when sweat evaporates from skin. The principal physical mechanism is:
A. Conduction into skinB. Latent heat of vaporisationC. Nuclear radiationD. Compression heatingCorrect: B. Latent heat of vaporisation
Explanation: Evaporation requires latent heat, which is taken from the body and cools it.
Key Concept / Clinical Relevance: Thermoregulation
Q15. At constant temperature, Boyle’s law states that for a fixed amount of gas:
A. P ∝ VB. P/T = constantC. PV = constantD. V/T = constantCorrect: C. PV = constant
Explanation: For an isothermal ideal gas process, pressure is inversely proportional to volume.
Key Concept / Clinical Relevance: Gas laws
Q16. The first law of thermodynamics is fundamentally a statement of conservation of:
A. ChargeB. MomentumC. Mass onlyD. EnergyCorrect: D. Energy
Explanation: Energy added as heat is partitioned into change in internal energy and work.
Key Concept / Clinical Relevance: Thermodynamics
Q17. Entropy of an isolated system undergoing a spontaneous irreversible process generally:
A. IncreasesB. DecreasesC. Remains exactly zeroD. Becomes negativeCorrect: A. Increases
Explanation: The second law requires total entropy not to decrease for an isolated system.
Key Concept / Clinical Relevance: Entropy
Q18. During quiet inspiration, alveolar pressure briefly becomes slightly subatmospheric because:
A. Lung volume decreasesB. Thoracic volume increasesC. Airway resistance becomes zeroD. Gas temperature doublesCorrect: B. Thoracic volume increases
Explanation: Expansion increases gas volume and lowers alveolar pressure, drawing air inward.
Key Concept / Clinical Relevance: Pressure–volume relationship in ventilation
Q19. Coulomb force between two point charges varies with separation r as:
A. rB. 1/rC. 1/r²D. r²Correct: C. 1/r²
Explanation: Coulomb’s law gives F ∝ 1/r².
Key Concept / Clinical Relevance: Electrostatics
Q20. Electric potential difference is energy transferred per unit:
A. CurrentB. ResistanceC. PowerD. ChargeCorrect: D. Charge
Explanation: Voltage is work or energy per coulomb.
Key Concept / Clinical Relevance: Electric potential
Q21. Two identical resistors R connected in parallel have equivalent resistance:
A. R/2B. 2RC. RD. R²Correct: A. R/2
Explanation: 1/Req = 1/R + 1/R = 2/R.
Key Concept / Clinical Relevance: Parallel circuits
Q22. A 12 V source drives 2 A through a resistor. Its resistance is:
A. 10 ΩB. 6 ΩC. 14 ΩD. 24 ΩCorrect: B. 6 Ω
Explanation: R = V/I = 12/2 = 6 Ω.
Key Concept / Clinical Relevance: Ohm’s law
Q23. An ECG records voltage differences at the body surface. If electrode contact resistance rises markedly, the tracing is most likely to show:
A. Improved signal qualityB. Higher cardiac outputC. More noise/artifactD. Faster conduction velocityCorrect: C. More noise/artifact
Explanation: Poor electrode contact raises impedance and increases susceptibility to noise and artifact.
Key Concept / Clinical Relevance: Biomedical electrical measurement
Q24. A capacitor stores energy primarily in its:
A. Magnetic fieldB. Mechanical motionC. MassD. Electric fieldCorrect: D. Electric field
Explanation: Energy in a capacitor is stored in the electric field between conductors.
Key Concept / Clinical Relevance: Capacitance
Q25. The magnetic force on a stationary electric charge is:
A. ZeroB. MaximumC. qED. Always centripetalCorrect: A. Zero
Explanation: Magnetic force q(v × B) is zero when v = 0.
Key Concept / Clinical Relevance: Magnetism
Q26. Faraday’s law relates induced emf to the rate of change of:
A. Electric resistanceB. Magnetic fluxC. MassD. TemperatureCorrect: B. Magnetic flux
Explanation: An emf is induced when magnetic flux through a circuit changes.
Key Concept / Clinical Relevance: Electromagnetic induction
Q27. The rms voltage of a sinusoidal AC supply with peak voltage V₀ is:
A. V₀B. V₀/2C. V₀/√2D. √2V₀Correct: C. V₀/√2
Explanation: For a sinusoid, Vrms = Vpeak/√2.
Key Concept / Clinical Relevance: Alternating current
Q28. A defibrillator stores electrical energy before discharge. The component chiefly responsible is a:
A. Transformer onlyB. Diode onlyC. ResistorD. CapacitorCorrect: D. Capacitor
Explanation: A charged capacitor can rapidly release stored electrical energy during defibrillation.
Key Concept / Clinical Relevance: Defibrillator physics
Q29. Sound intensity is proportional to the square of the wave’s:
A. AmplitudeB. Frequency onlyC. Wavelength onlyD. PeriodCorrect: A. Amplitude
Explanation: For a given medium, intensity is proportional to amplitude squared.
Key Concept / Clinical Relevance: Wave intensity
Q30. Doppler frequency shift is produced primarily by:
A. Diffraction onlyB. Change in source–observer relative motionC. Total internal reflectionD. PolarisationCorrect: B. Change in source–observer relative motion
Explanation: Relative motion changes the observed frequency.
Key Concept / Clinical Relevance: Doppler effect
Q31. The refractive index n of a medium is defined as:
A. v/cB. cvC. c/vD. c+vCorrect: C. c/v
Explanation: n = speed of light in vacuum divided by speed in the medium.
Key Concept / Clinical Relevance: Refraction
Q32. A lens of focal length +0.5 m has optical power:
A. +0.5 DB. −2 DC. +5 DD. +2 DCorrect: D. +2 D
Explanation: P = 1/f(m) = 1/0.5 = +2 D.
Key Concept / Clinical Relevance: Lens power
Q33. A myopic eye is commonly corrected using a:
A. Diverging lensB. Converging lensC. Cylindrical lens in every caseD. Plane mirrorCorrect: A. Diverging lens
Explanation: A concave/diverging lens shifts the far-point image onto the retina.
Key Concept / Clinical Relevance: Optics of refractive error
Q34. Total internal reflection requires light to travel:
A. From lower to higher refractive index at any angleB. From higher to lower refractive index above the critical angleC. Only through vacuumD. Perpendicular to every interfaceCorrect: B. From higher to lower refractive index above the critical angle
Explanation: TIR occurs from optically denser to rarer medium when incidence exceeds the critical angle.
Key Concept / Clinical Relevance: Fibre optics
Q35. The resolving power of an optical system generally improves when wavelength:
A. IncreasesB. Equals zero onlyC. DecreasesD. Does not matterCorrect: C. Decreases
Explanation: Diffraction-limited resolution improves at shorter wavelength.
Key Concept / Clinical Relevance: Optical resolution
Q36. In the photoelectric effect, increasing light frequency above threshold primarily increases the emitted electron’s maximum:
A. Number onlyB. MassC. ChargeD. Kinetic energyCorrect: D. Kinetic energy
Explanation: Kmax = hf − work function.
Key Concept / Clinical Relevance: Photoelectric effect
Q37. The energy of a photon is:
A. hc/λB. hλ/cC. cλ/hD. h/(cλ)Correct: A. hc/λ
Explanation: Photon energy E = hf = hc/λ.
Key Concept / Clinical Relevance: Quantum physics
Q38. A radiograph is made with a higher tube voltage (kVp). The X-ray beam generally becomes:
A. Less penetratingB. More penetratingC. Non-ionisingD. MonochromaticCorrect: B. More penetrating
Explanation: Higher kVp increases photon energies and beam penetrability.
Key Concept / Clinical Relevance: X-ray physics
Q39. Half-life is the time required for the number of undecayed radioactive nuclei to fall to:
A. 75%B. 25%C. 50%D. 10%Correct: C. 50%
Explanation: By definition, one half-life reduces the undecayed population to one-half.
Key Concept / Clinical Relevance: Radioactivity
Q40. Which radiation has the greatest mass among these?
A. Gamma rayB. X-rayC. Beta particleD. Alpha particleCorrect: D. Alpha particle
Explanation: An alpha particle is a helium nucleus with two protons and two neutrons.
Key Concept / Clinical Relevance: Nuclear radiation
Q41. The SI unit of absorbed radiation dose is:
A. GrayB. SievertC. BecquerelD. CoulombCorrect: A. Gray
Explanation: The gray is one joule of ionising radiation energy absorbed per kilogram.
Key Concept / Clinical Relevance: Radiation dosimetry
Q42. During diagnostic ultrasound, a strong echo occurs at a tissue boundary mainly when there is a large difference in:
A. Electric chargeB. Acoustic impedanceC. RadioactivityD. TemperatureCorrect: B. Acoustic impedance
Explanation: Reflection increases with acoustic impedance mismatch across an interface.
Key Concept / Clinical Relevance: Ultrasound physics
Q43. Increasing ultrasound frequency generally produces:
A. Worse resolution and more penetrationB. No change in resolutionC. Better resolution but less penetrationD. Infinite penetrationCorrect: C. Better resolution but less penetration
Explanation: Higher frequency shortens wavelength, improving resolution but increasing attenuation.
Key Concept / Clinical Relevance: Ultrasound trade-off
Q44. In pulse oximetry, oxygen saturation is estimated using differential absorption of approximately:
A. Ultraviolet and X-raysB. Gamma and radio wavesC. Green light onlyD. Red and infrared lightCorrect: D. Red and infrared light
Explanation: Oxy- and deoxyhaemoglobin absorb red and infrared wavelengths differently.
Key Concept / Clinical Relevance: Pulse oximetry
Q45. MRI primarily detects signals from nuclei with magnetic moments, clinically dominated by:
A. Hydrogen protonsB. Calcium ionsC. Electrons in ironD. Carbon dioxide moleculesCorrect: A. Hydrogen protons
Explanation: Hydrogen is abundant in water and fat and has a strong MR signal.
Key Concept / Clinical Relevance: MRI fundamentals
Q46. A patient moves during an MRI acquisition. The most direct image consequence is:
A. Ionising radiation burnB. Motion artifact/ghostingC. Higher CT numberD. Doppler aliasingCorrect: B. Motion artifact/ghosting
Explanation: Motion during spatial encoding produces misregistration and ghosting artifacts.
Key Concept / Clinical Relevance: MRI artifacts
Q47. CT attenuation is commonly expressed using:
A. DioptresB. DecibelsC. Hounsfield unitsD. TeslasCorrect: C. Hounsfield units
Explanation: CT numbers are reported in Hounsfield units relative to water.
Key Concept / Clinical Relevance: CT physics
Q48. PET imaging detects pairs of photons produced after:
A. Alpha decayB. Nuclear fissionC. Ultrasound reflectionD. Positron–electron annihilationCorrect: D. Positron–electron annihilation
Explanation: Annihilation produces two approximately 511-keV photons emitted nearly opposite each other.
Key Concept / Clinical Relevance: PET physics
Q49. A pulse oximeter gives an unexpectedly low reading in a patient with cold, poorly perfused fingers. The most relevant physical limitation is:
A. Weak pulsatile optical signalB. Excess X-ray attenuationC. High acoustic impedanceD. Nuclear spin saturationCorrect: A. Weak pulsatile optical signal
Explanation: Low peripheral perfusion reduces the pulsatile arterial component required for reliable photoplethysmography.
Key Concept / Clinical Relevance: Pulse oximetry limitations
Q50. For laminar blood flow, halving vessel radius while all else remains constant changes flow to approximately:
A. 1/2B. 1/16C. 1/4D. 1/8Correct: B. 1/16
Explanation: Poiseuille’s law gives Q ∝ r⁴; (1/2)⁴ = 1/16.
Key Concept / Clinical Relevance: Hemodynamics
Q51. A projectile is launched at speed u at 45° on level ground without air resistance. Its range is:
A. u²/2gB. 2u²/gC. u²/gD. ugCorrect: C. u²/g
Explanation: R = u² sin2θ/g; at 45°, sin90° = 1.
Key Concept / Clinical Relevance: Projectile motion
Q52. A 70 kg patient lies on a mattress. If the effective contact area doubles while weight is unchanged, average interface pressure becomes:
A. TwiceB. Four timesC. UnchangedD. HalfCorrect: D. Half
Explanation: Pressure = force/area, so doubling area halves average pressure.
Key Concept / Clinical Relevance: Pressure injury biomechanics
Q53. For a rigid body with moment of inertia I and angular speed ω, rotational kinetic energy is:
A. ½Iω²B. IωC. I²ω/2D. ½I²ωCorrect: A. ½Iω²
Explanation: Rotational kinetic energy is ½Iω².
Key Concept / Clinical Relevance: Rotational dynamics
Q54. Blood flows through a stenosis whose radius is 60% of the original. Under ideal Poiseuille conditions and unchanged ΔP, flow becomes approximately:
A. 36%B. 13%C. 21.6%D. 60%Correct: B. 13%
Explanation: Q scales as r⁴; 0.6⁴ = 0.1296, about 13%.
Key Concept / Clinical Relevance: Stenosis and Poiseuille law
Q55. For steady incompressible flow, the continuity equation implies that when cross-sectional area decreases, mean velocity:
A. Decreases proportionallyB. Remains fixedC. IncreasesD. Becomes zeroCorrect: C. Increases
Explanation: A₁v₁ = A₂v₂, so velocity rises as area falls.
Key Concept / Clinical Relevance: Continuity equation
Q56. Bernoulli’s principle predicts that, at the same height in ideal streamline flow, a region of higher fluid velocity has:
A. Higher static pressureB. Identical pressure alwaysC. Zero kinetic energyD. Lower static pressureCorrect: D. Lower static pressure
Explanation: Along a streamline, increased kinetic-energy density is associated with reduced static pressure.
Key Concept / Clinical Relevance: Bernoulli principle
Q57. Across a severe arterial stenosis, Doppler velocity rises from 1 to 4 m/s. Using the simplified Bernoulli relation ΔP ≈ 4v², the estimated gradient is:
A. 64 mmHgB. 16 mmHgC. 32 mmHgD. 80 mmHgCorrect: A. 64 mmHg
Explanation: At v = 4 m/s, ΔP ≈ 4 × 16 = 64 mmHg.
Key Concept / Clinical Relevance: Doppler haemodynamics
Q58. Laplace’s law for a spherical interface gives pressure difference ΔP proportional to:
A. TrB. T/rC. r/TD. 1/(Tr)Correct: B. T/r
Explanation: For a sphere ΔP = 2T/r.
Key Concept / Clinical Relevance: Laplace law
Q59. Two alveoli have equal surface tension but radii r and 2r. Without surfactant, the smaller alveolus has internal pressure:
A. Half as largeB. The sameC. Twice as largeD. Four times as largeCorrect: C. Twice as large
Explanation: For an alveolus approximated as a sphere, P ∝ 1/r.
Key Concept / Clinical Relevance: Alveolar stability
Q60. Pulmonary surfactant particularly stabilises small alveoli because it:
A. Raises surface tension most in small alveoliB. Eliminates gas pressureC. Makes air incompressibleD. Lowers surface tension, especially as alveoli become smallerCorrect: D. Lowers surface tension, especially as alveoli become smaller
Explanation: Concentrated surfactant at low lung volumes lowers surface tension and reduces collapse tendency.
Key Concept / Clinical Relevance: Surfactant physics
Q61. For a gas mixture, Dalton’s law states total pressure equals:
A. Sum of partial pressuresB. Product of partial pressuresC. Mean molecular weightD. Osmotic pressureCorrect: A. Sum of partial pressures
Explanation: The total pressure of an ideal gas mixture is the sum of component partial pressures.
Key Concept / Clinical Relevance: Partial pressures
Q62. At constant temperature, compressing an ideal gas to half its volume changes pressure to:
A. HalfB. DoubleC. Four timesD. UnchangedCorrect: B. Double
Explanation: Boyle’s law gives P₁V₁=P₂V₂.
Key Concept / Clinical Relevance: Gas compression
Q63. During positive-pressure ventilation, increasing tidal volume without changing airway resistance most directly increases the pressure needed to overcome:
A. Electrical impedanceB. Magnetic fluxC. Elastic loadD. Optical attenuationCorrect: C. Elastic load
Explanation: Greater volume displacement increases elastic recoil pressure according to compliance.
Key Concept / Clinical Relevance: Ventilator mechanics
Q64. If lung compliance is 40 mL/cmH₂O and a 400 mL tidal volume is delivered quasi-statically, the elastic pressure change is approximately:
A. 5 cmH₂OB. 16 cmH₂OC. 40 cmH₂OD. 10 cmH₂OCorrect: D. 10 cmH₂O
Explanation: ΔP = ΔV/C = 400/40 = 10 cmH₂O.
Key Concept / Clinical Relevance: Compliance
Q65. For diffusion across a membrane, Fick’s law predicts transfer rate increases with:
A. Surface areaB. Membrane thicknessC. Inverse concentration gradientD. Molecular size aloneCorrect: A. Surface area
Explanation: Diffusion rate is proportional to area and gradient and inversely proportional to thickness.
Key Concept / Clinical Relevance: Fick’s law
Q66. A patient develops pulmonary edema that doubles effective diffusion distance. If all other factors remain constant, gas diffusion rate is expected to:
A. DoubleB. HalveC. QuadrupleD. Remain unchangedCorrect: B. Halve
Explanation: Fick’s law makes diffusion inversely proportional to membrane thickness.
Key Concept / Clinical Relevance: Gas diffusion
Q67. A capacitor of 100 μF charged to 200 V stores approximately:
A. 0.2 JB. 1 JC. 2 JD. 20 JCorrect: C. 2 J
Explanation: E = ½CV² = 0.5 × 100×10⁻⁶ × 40000 = 2 J.
Key Concept / Clinical Relevance: Capacitor energy
Q68. In an RC circuit, the time constant is:
A. R/CB. 1/RCC. R+CD. RCCorrect: D. RC
Explanation: The characteristic charging/discharging time constant is τ = RC.
Key Concept / Clinical Relevance: RC circuits
Q69. A defibrillator with capacitance 200 μF is charged to 1000 V. Stored energy is:
A. 100 JB. 10 JC. 50 JD. 200 JCorrect: A. 100 J
Explanation: E = ½CV² = 0.5 × 200×10⁻⁶ × 10⁶ = 100 J.
Key Concept / Clinical Relevance: Defibrillator energy
Q70. The impedance of an ideal capacitor in AC has magnitude:
A. 2πfCB. 1/(2πfC)C. 2πf/CD. C/(2πf)Correct: B. 1/(2πfC)
Explanation: Capacitive reactance Xc = 1/(2πfC).
Key Concept / Clinical Relevance: AC impedance
Q71. A transformer ideally changes voltage according to the ratio of:
A. ResistancesB. FrequenciesC. Turns in secondary to primaryD. Core massesCorrect: C. Turns in secondary to primary
Explanation: Vs/Vp = Ns/Np for an ideal transformer.
Key Concept / Clinical Relevance: Transformers
Q72. An isolation transformer in medical equipment principally reduces risk by:
A. Increasing radiation doseB. Amplifying ECG voltageC. Creating DC from ACD. Breaking direct conductive connection to mainsCorrect: D. Breaking direct conductive connection to mains
Explanation: Galvanic isolation limits hazardous current paths between mains and patient circuits.
Key Concept / Clinical Relevance: Electrical safety
Q73. For a charged particle moving perpendicular to a uniform magnetic field, the magnetic force does:
A. No workB. Positive work continuouslyC. Negative work continuouslyD. Work only at low speedCorrect: A. No work
Explanation: Magnetic force is perpendicular to velocity, changing direction but not speed.
Key Concept / Clinical Relevance: Lorentz force
Q74. Lenz’s law determines the induced current direction so that its magnetic effect:
A. Enhances the flux changeB. Opposes the flux changeC. Is unrelated to fluxD. Always points northCorrect: B. Opposes the flux change
Explanation: The induced response opposes the change that produced it.
Key Concept / Clinical Relevance: Lenz’s law
Q75. In MRI, the Larmor angular frequency ω₀ is proportional to:
A. 1/B₀B. B₀² onlyC. B₀D. Gradient slew rate onlyCorrect: C. B₀
Explanation: ω₀ = γB₀.
Key Concept / Clinical Relevance: Larmor precession
Q76. Moving from a 1.5 T to a 3 T MRI scanner approximately does what to proton Larmor frequency?
A. Halves itB. Quadruples itC. Leaves it unchangedD. Doubles itCorrect: D. Doubles it
Explanation: Larmor frequency is directly proportional to static field strength.
Key Concept / Clinical Relevance: MRI field strength
Q77. T1 relaxation describes recovery of:
A. Longitudinal magnetisationB. Transverse coherenceC. Gradient strengthD. X-ray attenuationCorrect: A. Longitudinal magnetisation
Explanation: T1 is spin-lattice recovery of longitudinal magnetisation.
Key Concept / Clinical Relevance: MRI relaxation
Q78. T2 relaxation describes decay of:
A. Longitudinal magnetisation onlyB. Transverse magnetisation due to spin-spin dephasingC. Proton numberD. Static magnetic fieldCorrect: B. Transverse magnetisation due to spin-spin dephasing
Explanation: T2 is the time constant of transverse spin-spin dephasing.
Key Concept / Clinical Relevance: MRI relaxation
Q79. A spin-echo sequence uses a 180° pulse primarily to reduce signal loss from:
A. True T2 interactionsB. Proton densityC. Static field inhomogeneity dephasingD. Longitudinal recoveryCorrect: C. Static field inhomogeneity dephasing
Explanation: The 180° refocusing pulse reverses dephasing from static field variations, yielding T2 rather than T2*.
Key Concept / Clinical Relevance: MRI spin echo
Q80. In diagnostic ultrasound, axial resolution is improved most directly by:
A. Longer spatial pulse lengthB. Lower sound speedC. Higher beam widthD. Shorter spatial pulse lengthCorrect: D. Shorter spatial pulse length
Explanation: Axial resolution is approximately half the spatial pulse length.
Key Concept / Clinical Relevance: Ultrasound resolution
Q81. Doppler aliasing in pulsed-wave ultrasound occurs when Doppler shift exceeds:
A. Nyquist limitB. The acoustic impedanceC. Attenuation coefficientD. Critical angleCorrect: A. Nyquist limit
Explanation: The maximum unambiguous sampled frequency is half the pulse repetition frequency.
Key Concept / Clinical Relevance: Doppler aliasing
Q82. A Doppler study shows aliasing at high blood velocity. Which change can raise the Nyquist limit?
A. Decrease PRFB. Increase PRFC. Increase wavelength onlyD. Set Doppler angle to 90°Correct: B. Increase PRF
Explanation: Nyquist limit = PRF/2; increasing PRF increases the measurable shift before aliasing.
Key Concept / Clinical Relevance: Pulsed Doppler
Q83. For Doppler ultrasound, measured frequency shift approaches zero when the beam-flow angle approaches:
A. 0°B. 30°C. 90°D. 60°Correct: C. 90°
Explanation: Doppler shift contains cosθ; cos90° = 0.
Key Concept / Clinical Relevance: Doppler angle
Q84. Acoustic impedance Z is the product of tissue density and:
A. FrequencyB. Wavelength squaredC. Attenuation onlyD. Sound speedCorrect: D. Sound speed
Explanation: Z = ρc.
Key Concept / Clinical Relevance: Acoustic impedance
Q85. At a soft-tissue–air interface, ultrasound transmission is poor chiefly because of:
A. Large acoustic impedance mismatchB. Minimal impedance mismatchC. Identical sound speedsD. No reflectionCorrect: A. Large acoustic impedance mismatch
Explanation: The large impedance difference causes strong reflection, which is why coupling gel is used.
Key Concept / Clinical Relevance: Ultrasound coupling
Q86. The minimum resolvable separation of two point objects due to diffraction is approximately proportional to:
A. NA/λB. λ/NAC. λ×NA²D. 1/(λNA)Correct: B. λ/NA
Explanation: Resolution limit scales with wavelength divided by numerical aperture.
Key Concept / Clinical Relevance: Diffraction limit
Q87. In optical fibres, increasing the numerical aperture generally increases the:
A. Critical wavelength onlyB. Photon energyC. Acceptance angleD. Speed of light in vacuumCorrect: C. Acceptance angle
Explanation: Higher numerical aperture permits a wider cone of accepted rays.
Key Concept / Clinical Relevance: Fibre optics
Q88. An endoscope uses optical fibres to transmit light around bends primarily by:
A. Compton scatteringB. Photoelectric absorptionC. Nuclear resonanceD. Total internal reflectionCorrect: D. Total internal reflection
Explanation: Light remains guided within the core through repeated total internal reflection.
Key Concept / Clinical Relevance: Endoscopy optics
Q89. For X-ray photons in diagnostic imaging, photoelectric absorption probability increases strongly with:
A. Higher atomic number and lower photon energyB. Lower atomic numberC. Higher photon energy onlyD. Lower density onlyCorrect: A. Higher atomic number and lower photon energy
Explanation: Photoelectric interaction rises steeply with atomic number and falls with photon energy.
Key Concept / Clinical Relevance: X-ray interactions
Q90. Compton scattering depends primarily on the material’s:
A. Atomic number to the fourth powerB. Electron densityC. Magnetic susceptibility onlyD. Optical refractive indexCorrect: B. Electron density
Explanation: In the diagnostic range, Compton probability is mainly related to electron density.
Key Concept / Clinical Relevance: Compton effect
Q91. After iodinated contrast is administered for CT, vessels appear more attenuating chiefly because iodine:
A. Eliminates Compton scatterB. Produces ultrasoundC. Has a relatively high atomic numberD. Lowers photon energy to zeroCorrect: C. Has a relatively high atomic number
Explanation: Iodine’s high atomic number increases X-ray attenuation, especially photoelectric absorption.
Key Concept / Clinical Relevance: CT contrast physics
Q92. The Hounsfield unit of water is defined as approximately:
A. −1000B. −100C. +1000D. 0Correct: D. 0
Explanation: Water is the reference at 0 HU; air is about −1000 HU.
Key Concept / Clinical Relevance: CT numbers
Q93. If CT slice thickness is reduced while other factors are unchanged, partial-volume averaging generally:
A. DecreasesB. IncreasesC. Becomes infiniteD. Is unrelatedCorrect: A. Decreases
Explanation: Thinner slices contain fewer mixed tissues and reduce partial-volume effects.
Key Concept / Clinical Relevance: CT spatial resolution
Q94. A small lesion adjacent to dense bone is obscured on thick CT slices but becomes visible on thinner reconstructions. The key improvement is reduced:
A. Larmor frequencyB. Partial-volume averagingC. Radioactive decayD. Doppler shiftCorrect: B. Partial-volume averaging
Explanation: Thinner slices reduce averaging of different tissues within a voxel.
Key Concept / Clinical Relevance: CT partial-volume effect
Q95. Radioactive activity measured in becquerels represents:
A. Absorbed joules/kgB. Biological weightingC. Disintegrations per secondD. Photon energy in eVCorrect: C. Disintegrations per second
Explanation: 1 Bq equals one nuclear transformation per second.
Key Concept / Clinical Relevance: Radioactivity units
Q96. A staff member steps from 1 m to 2 m from an approximately point-like radiation source. Ignoring scatter, exposure rate becomes about:
A. DoubleB. HalfC. One-eighthD. One-quarterCorrect: D. One-quarter
Explanation: Inverse-square behavior gives I₂/I₁=(1/2)²=1/4.
Key Concept / Clinical Relevance: Radiation safety
Q97. A PET tracer emits a positron. Before annihilation, positron travel in tissue contributes chiefly to:
A. A limit on spatial resolutionB. Improved spatial resolutionC. Higher MRI signalD. Doppler aliasingCorrect: A. A limit on spatial resolution
Explanation: Positron range separates decay from annihilation location and blurs spatial localisation.
Key Concept / Clinical Relevance: PET resolution
Q98. A pulse oximeter may display a misleading saturation in carbon monoxide poisoning because conventional two-wavelength devices cannot reliably distinguish:
A. Water from plasmaB. Oxyhaemoglobin from carboxyhaemoglobinC. Sodium from potassiumD. Venous from arterial pressureCorrect: B. Oxyhaemoglobin from carboxyhaemoglobin
Explanation: Standard pulse oximetry has limited spectral discrimination and may count carboxyhaemoglobin as oxyhaemoglobin.
Key Concept / Clinical Relevance: Optical spectroscopy limitations
Q99. A mechanically ventilated patient has a capnogram with a sloping expiratory plateau. From a physical measurement standpoint, this most directly reflects:
A. X-ray attenuationB. Electrical capacitanceC. Nonuniform emptying and gas mixingD. Magnetic resonanceCorrect: C. Nonuniform emptying and gas mixing
Explanation: Unequal time constants and heterogeneous exhalation produce a rising alveolar plateau.
Key Concept / Clinical Relevance: Capnography waveform physics
Q100. A patient with marked polycythaemia has increased blood viscosity. Under otherwise comparable conditions, vascular resistance tends to:
A. DecreaseB. Become zeroC. Be independent of viscosityD. IncreaseCorrect: D. Increase
Explanation: Laminar resistance is directly proportional to viscosity.
Key Concept / Clinical Relevance: Blood viscosity and resistance