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Question 1. Which phenomenon explains why a single slit produces a central bright fringe surrounded by progressively fainter bands? A) Refraction B) Diffraction C) Polarization D) Dispersion Answer: B Explanation: Diffraction occurs when waves encounter an obstacle or aperture comparable to their wavelength, causing interference that creates a central maximum and side minima. Question 2. The refractive index of a medium is defined as the ratio of: A) Speed of light in vacuum to speed of light in the medium B) Frequency of light in vacuum to frequency in the medium C) Wavelength in the medium to wavelength in vacuum D) Energy of a photon in vacuum to energy in the medium Answer: A Explanation: n = c / v, where c is the speed of light in vacuum and v is its speed in the material. Question 3. Which part of the electromagnetic spectrum has photon energies sufficient to cause electronic transitions in DNA but not to ionize atoms? A) Ultraviolet-C B) Visible light C) Infrared D) X-rays Answer: A Explanation: UV-C photons have energies (~5– 10 eV) that can break molecular bonds and cause DNA damage without the higher energies needed for ionization. Question 4. In Snell’s law, n₁ sin θ₁ = n₂ sin θ₂, what does θ represent?
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A) Angle between the incident ray and the normal to the interface B) Angle between the refracted ray and the surface plane C) Angle of polarization of the electric field D) Angle of diffraction at the aperture edge Answer: A Explanation: θ is measured from the normal (perpendicular) to the interface for both incident and refracted rays. Question 5. A surface that reflects light equally in all directions is called: A) Specular B) Diffuse C) Metallic D) Anisotropic Answer: B Explanation: Diffuse (Lambertian) surfaces scatter incident light uniformly, producing no clear reflections. Question 6. Which of the following best describes Rayleigh scattering? A) Scattering by particles much larger than the wavelength B) Scattering that is independent of wavelength C) Scattering that varies inversely with the fourth power of wavelength D) Scattering that only occurs in vacuum Answer: C Explanation: Rayleigh scattering intensity ∝ 1/λ⁴, which is why shorter (blue) wavelengths scatter more strongly. Question 7. The unit “lux” measures: A) Total radiant power emitted by a source B) Luminous intensity per steradian C) Illuminance, i.e., luminous flux per unit area
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Answer: B Explanation: At Brewster’s angle, the reflected ray is linearly polarized with the electric field perpendicular to the plane of incidence (vertical for a horizontal surface). Question 11. In a CCD sensor, charge packets are transferred to a readout register by: A) Magnetic fields B) Mechanical rollers C) Clocked voltage potentials D) Thermal diffusion Answer: C Explanation: Clocked voltage patterns shift accumulated charge across the pixel array to the output node. Question 12. The “reciprocity failure” most commonly occurs in which photographic medium? A) Digital CMOS sensors B) Traditional silver halide film C) Infrared thermal cameras D) X-ray phosphor plates Answer: B Explanation: Film exhibits non-linear response when exposure time is extremely long or short, deviating from the reciprocity law. Question 13. The term “dynamic range” of a sensor refers to: A) The ratio of maximum to minimum detectable luminance B) The total number of pixels on the sensor C) The speed at which the sensor can read out data D) The range of wavelengths the sensor is sensitive to Answer: A
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Explanation: Dynamic range quantifies the span between the darkest and brightest signals a sensor can record without saturation or noise domination. Question 14. Which of the following is a primary cause of chromatic aberration in a simple lens? A) Non-uniform illumination B) Variation of refractive index with wavelength (dispersion) C) Surface scratches on the lens D) Polarization of incoming light Answer: B Explanation: Dispersion causes different wavelengths to focus at different distances, producing color fringing. Question 15. In radiometry, the unit “watt per steradian” measures: A) Luminous intensity B) Radiant intensity C) Luminous flux D) Radiant flux Answer: B Explanation: Radiant intensity is power emitted per unit solid angle, expressed in W·sr⁻¹. Question 16. Which of the following best describes a “specular” reflection? A) Light scattered uniformly in all directions B) Light reflected at the same angle as the incident angle C) Light absorbed and re-emitted at a longer wavelength D) Light that undergoes total internal reflection Answer: B Explanation: Specular reflection follows the law of reflection, with incident and reflected angles equal relative to the normal.
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C) Interference D) Polarization Answer: C Explanation: Interference results from the superposition of coherent waves, leading to constructive and destructive regions. Question 21. Which of the following devices converts photons directly into an electrical signal without a mechanical shutter? A) Photographic film B) Photodiode array C) Mechanical camera shutter D) Fluorescent lamp Answer: B Explanation: Photodiodes generate current when photons are absorbed, enabling electronic imaging without moving parts. Question 22. The “albedo” of a surface is defined as: A) The ratio of reflected to incident radiant flux B) The absolute amount of light absorbed C) The wavelength at which the surface emits most radiation D) The angle at which specular reflection occurs Answer: A Explanation: Albedo is a dimensionless reflectance coefficient (0–1) indicating how much incident light is reflected. Question 23. When a photon of wavelength 400 nm is absorbed by a material, the energy transferred is: A) 1.55 eV B) 2.48 eV C) 3.10 eV
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D) 4.95 eV Answer: D Explanation: E = 1240 eV·nm / 400 nm ≈ 3.10 eV (actually 3.10 eV). Correction: 1240/400 ≈ 3.10 eV, so option C is correct. Explanation: Using the photon energy formula yields approximately 3.10 eV. Question 24. Which law describes the relationship between the intensity of transmitted light, the path length, and the concentration of an absorbing species? A) Snell’s law B) Beer-Lambert law C) Planck’s law D) Stefan-Boltzmann law Answer: B Explanation: I = I₀ e^(−α c l) expresses exponential attenuation with concentration (c) and path length (l). Question 25. The term “spectral power distribution” (SPD) refers to: A) The distribution of photon counts across time B) The variation of radiant power with wavelength C) The angular distribution of light from a source D) The polarization state of emitted photons Answer: B Explanation: SPD plots emitted power (or intensity) versus wavelength, characterising a light source’s colour. Question 26. In a polarizing filter, the axis that allows transmission of electric-field vectors is called the: A) Fast axis B) Slow axis C) Transmission axis
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Answer: B Explanation: Lens flare introduces stray light, causing glare, ghost images, and loss of contrast. Question 30. The “color temperature” of a light source measured in Kelvin primarily influences: A) The intensity of the source B) The spectral distribution perceived as “warm” or “cool” C) The polarization state of emitted light D) The speed of light in the medium Answer: B Explanation: Higher Kelvin values correspond to “cool” bluish light; lower values to “warm” reddish tones. Question 31. Which of the following best describes total internal reflection? A) Light reflecting from a surface with a higher to lower refractive index at any angle B) Light transmitting through a medium with no change in direction C) Light reflecting completely when incident beyond the critical angle from a higher-index medium to a lower-index medium D) Light being absorbed and re-emitted at a longer wavelength Answer: C Explanation: When the incidence angle exceeds the critical angle, all light is reflected back into the higher-index medium. Question 32. In digital imaging, “noise” that appears as random speckles is most often associated with: A) High ISO settings B) Low aperture values (large openings) C) Short exposure times D) Over-exposure of highlights
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Answer: A Explanation: Raising ISO amplifies the sensor’s signal and also its electronic noise, producing speckle-like artifacts. Question 33. The principle that the sum of the angles of incidence and reflection equals: A) 90° B) 180° C) 360° D) 0° Answer: B Explanation: For specular reflection, θ_i + θ_r = 180° measured with respect to the surface plane, equivalent to the law of reflection where the angles relative to the normal are equal. Question 34. When a light beam passes through a polarizer oriented at 45° relative to the incoming polarization, the transmitted intensity is: A) 100 % of the incident intensity B) 75 % of the incident intensity C) 50 % of the incident intensity D) 25 % of the incident intensity Answer: C Explanation: According to Malus’s law, I = I₀ cos²θ; cos²45° = 0.5, so half the intensity passes. **Question 35. Which of the following instruments directly measures luminous flux? ** A) Radiometer B) Photometer C) Spectrophotometer D) Lux meter
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Explanation: An achromatic doublet combines glasses with different dispersion to bring two wavelengths to a common focus. Question 39. In the context of photometry, the “candela” is the SI unit of: A) Luminous flux B) Luminous intensity C) Illuminance D) Luminance Answer: B Explanation: Candela measures luminous intensity in a given direction. Question 40. Which of the following is a primary ethical concern when manipulating light-based data in forensic imaging? A) Reducing file size for faster transmission B) Enhancing contrast to reveal hidden details C) Altering pixel values in a way that misrepresents the original scene D) Converting images to grayscale for easier analysis Answer: C Explanation: Modifying pixel data can create false evidence; ethical standards require preserving the integrity of original data. Question 41. The “inverse square law” fails for which of the following lighting situations? A) A point source in free space B) A distant star observed from Earth C) A large, diffuse source close to the subject D) A laser beam traveling a short distance Answer: C Explanation: When the source size is comparable to the distance, intensity does not follow a simple 1/d² relationship.
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Question 42. The phenomenon that allows a glass prism to separate white light into a spectrum is called: A) Diffraction B) Polarization C) Dispersion D) Interference Answer: C Explanation: Different wavelengths experience different refractive indices, causing angular separation. Question 43. Which of the following best describes “radiant exitance”? A) Power emitted per unit area of a surface B) Power received per unit area of a detector C) Power per unit solid angle in a given direction D) Power per unit wavelength interval Answer: A Explanation: Radiant exitance (also called radiant emittance) is the total radiant flux leaving a surface per unit area. Question 44. In the exposure triangle, increasing ISO while keeping aperture and shutter speed constant will: A) Decrease image brightness B) Increase image brightness C) Have no effect on brightness D) Change the colour balance Answer: B Explanation: Higher ISO amplifies sensor sensitivity, resulting in a brighter image for the same light amount.
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A) Maximum number of photons a pixel can store before saturating B) The total storage space on the memory card C) The battery life of the camera D) The dynamic range of the sensor Answer: A Explanation: Full-well capacity is the charge-holding ability of a pixel; exceeding it leads to clipping. Question 49. Which of the following best explains why a laser beam can remain collimated over long distances? A) High refractive index of the gain medium B) Coherence and low divergence due to stimulated emission C) Use of a polarizing filter in the cavity D) Continuous rotation of the output mirror Answer: B Explanation: Laser light is coherent and generated with a resonant cavity that limits divergence, preserving collimation. Question 50. The “K-ratio” in X-ray fluorescence analysis is used to determine: A) The ratio of incident to reflected X-rays B) The concentration of an element relative to a standard C) The polarization state of the emitted X-rays D) The energy distribution of the X-ray source Answer: B Explanation: K-ratio compares the intensity of characteristic X-ray peaks from a sample to those from a known standard, enabling quantitative analysis. Question 51. Which of the following statements about “polarizing sunglasses” is correct? A) They block all ultraviolet radiation but transmit all visible light.
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B) They preferentially absorb horizontally polarized glare, reducing eye strain. C) They convert linearly polarized light into circularly polarized light. D) They increase the overall luminous intensity reaching the eye. Answer: B Explanation: Polarized lenses absorb horizontal components of reflected light, which are the primary source of glare. Question 52. In photometry, the term “luminance” is defined as: A) Luminous flux per unit area per unit solid angle B) Total luminous flux emitted by a source C) Luminous intensity per unit area D) Luminous flux incident on a surface Answer: A Explanation: Luminance (cd/m²) measures the amount of light emitted or reflected in a particular direction per unit area. Question 53. The “critical angle” for total internal reflection depends on: A) The wavelength of light only B) The refractive indices of the two media C) The polarization state of the incident light D) The intensity of the incident beam Answer: B Explanation: Critical angle θ_c = arcsin(n₂/n₁) for n₁ > n₂; it depends solely on the two refractive indices. Question 54. Which of the following best describes “photon shot noise”? A) Noise arising from thermal agitation of electrons B) Statistical fluctuations in the number of photons detected C) Noise caused by imperfections in the lens coating D) Noise introduced during analog-to-digital conversion
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Explanation: Radiant flux (Φ) is the total power of electromagnetic radiation emitted, measured in watts. Question 58. Which of the following is the primary advantage of a CMOS sensor over a CCD for high-speed imaging? A) Higher quantum efficiency B) Lower readout noise C) Parallel pixel readout allowing faster frame rates D) Greater full-well capacity Answer: C Explanation: CMOS architecture enables each pixel to be read independently, supporting rapid data acquisition. Question 59. In a histogram of a digital photograph, a “clipping” at the right side indicates: A) Underexposed shadows B) Overexposed highlights that have lost detail C) Balanced exposure across tones D) Noise in the mid-tones Answer: B Explanation: Clipping on the high-end shows pixels at maximum value (e.g., 255), meaning detail in highlights is lost. Question 60. The “Kerr effect” is a nonlinear optical phenomenon where: A) Light is absorbed and re-emitted at a longer wavelength B) The refractive index of a material changes with the intensity of the electric field C) Light is scattered by particles comparable to its wavelength D) Photons are converted into electron-hole pairs Answer: B
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Explanation: The Kerr effect causes intensity-dependent refractive index changes, leading to phenomena like self-focusing. Question 61. Which of the following best describes a “Bessel beam”? A) A beam that diffracts rapidly over short distances B) A non-diffracting beam with an intensity profile described by a Bessel function C) A beam that changes polarization along its propagation axis D) A beam that is highly sensitive to atmospheric turbulence Answer: B Explanation: Bessel beams maintain their shape over extended distances due to their self-reconstructing nature. Question 62. The “Planck constant” (h) appears in which fundamental equation for photon energy? A) E = hc/λ B) E = c/λ C) E = h · frequency D) Both A and C Answer: D Explanation: Photon energy can be expressed as E = hν (C) and, using ν = c/λ, as E = hc/λ (A). Question 63. In the context of radiology, the “half-value layer” (HVL) of an X-ray beam is defined as: A) The thickness of material that reduces beam intensity by 50 % B) The distance at which the beam’s intensity falls to half its original value in free space C) The time required to deliver half the prescribed dose D) The wavelength at which the beam’s energy is halved Answer: A
