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Physical Optics MCQs for MDCAT Practice

Physics section, Physical Optics chapter. Up to eight free sample questions, each with the correct answer and a worked explanation. The full chapter opens in the app.

The bank has 14 active questions on this chapter. Your first 500 practice attempts are free, and every attempt includes a worked explanation.

  1. Question 1
    The phenomenon of polarization of light reveals that light wave
    • Are longitudinal.
    • Are extremely short.
    • Have a long wavelength.
    • Are transverse electromagnetic. (correct answer)
    Correct answer: D
    Polarization directly demonstrates light's transverse nature, where oscillations are perpendicular to wave propagation, a defining characteristic of transverse electromagnetic waves.
  2. Question 2
    The narrow slits of a diffraction grating are 5 × 10-4m apart. If a light ray of 5 × 10-7 m wavelength passes through the narrow slits, then the value of angle observed at the third-order bright spot is
    • 0.057°
    • 0.028°
    • 0.017°
    • 0.085° (correct answer)
    Correct answer: D
    Calculate the angle of a bright spot in a diffraction grating using the grating equation and given parameters for slit separation, wavelength, and order.
  3. Question 3
    All of the following are the conditions necessary for the interference of light EXCEPT
    • Light waves should be monochromatic.
    • Sources of the light waves must be coherent
    • Identical light waves should have constant phase difference.
    • Size of the obstacle must be similar to the wavelength of light waves. (correct answer)
    Correct answer: D
    Interference requires monochromatic, coherent light with a constant phase difference, not specific obstacle sizes.
  4. Question 4
    In Young’s double slit experiment the separation d between the slits is 2mm, the wavelength of the light used is 5896 A and the distance D between the screen and slits is 100cm. It is found that the angular width of the fringes is 0.20. To increase the fringe angular width to 0.21 with the same wavelength and D, the separation between the slits needs to be changed to
    • 1.8 mm
    • 2.1 mm
    • 1.7 mm
    • 1.9 mm (correct answer)
    Correct answer: D
    Young's double-slit experiment: Adjusting slit separation to achieve a desired fringe angular width, demonstrating the inverse relationship between slit separation and angular fringe width.
  5. Question 5
    Which of the following phenomena reveals that light waves are transverse waves? I. Diffraction П. Polarization III. Interference
    • I only
    • I and III
    • II and III
    • II only (correct answer)
    Correct answer: D
    Polarization is the key phenomenon demonstrating light's transverse nature, distinguishing it from longitudinal waves like sound.
  6. Question 6
    If a man moves, with a speed equal to 0.5 that of sound, away from a stationary source generating sound of frequency of 1000Hz, he would probably hear sound of frequency:
    • 1000 Hz
    • 750 Hz
    • 667 Hz (correct answer)
    • 500 Hz
    Correct answer: C
    This question tests the Doppler effect for sound when the observer is moving away from a stationary source, requiring calculation of the perceived frequency shift.
  7. Question 7
    In Young`s double slit experiment, if d is separation between two slits, is wavelength of light and is angle of line from center of slits to the point of observation on the screen; then for maxima (bright fringe); the formula is _______
    • 2dsin = m; m = 0, 1, 2, ...
    • dsin = (m+1/2); m = 0, 1, 2, ...
    • 2msin = d; m = 0, 1, 2, ...
    • dsin = m; m= 0, 1, 2, ... (correct answer)
    Correct answer: D
    This MCQ tests the condition for constructive interference (maxima) in Young's double-slit experiment, a fundamental concept in physical optics.
  8. Question 8
    In diffraction of light around an obstacle, the angle of diffraction is increased then:
    • The wavelength of incident light wave is decreased
    • The amplitude of the incident light wave is increased
    • The amplitude of the incident light wave is decreased
    • The wavelength of incident light wave is increased (correct answer)
    Correct answer: D
    Diffraction angle widens with longer wavelengths; amplitude affects intensity, not angular spread. Understand the relationship between wavelength, slit/obstacle size, and diffraction pattern.

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