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Free Optics MCQs with Answers

665 Optics MCQs from Physics, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.

Light is studied through reflection, refraction, dispersion, interference, diffraction and polarization, linking ray behavior with its wave nature. Questions may involve mirrors, lenses, optical instruments, refractive index and image formation, while geometrical optics deals with rays and wave optics explains effects such as interference and diffraction.

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665 questions · page 22 of 34

421. Which of the following experiments prove the particle nature of light?

  • A. Interference
  • B. Diffraction
  • C. Reflection
  • D. Photoelectric effect

Explanation: The photoelectric effect is an experiment that proves the particle nature of light.

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Correct answer: Photoelectric effect

422. For better results, actual spectrometer makes use of?

  • A. Capacitors
  • B. Diffraction grating
  • C. Mica window
  • D. Polarizers

Explanation: Diffraction gratings are widely used in spectrometers to disperse light into its constituent wavelengths.

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Correct answer: Diffraction grating

423. Sounds wave are not polarized in air because:

  • A. They are longitudinal waves
  • B. They are transverse waves
  • C. They need media for its propagation
  • D. They have shorter wave lengths

Explanation: Longitudinal waves' oscillations are parallel to their propagation, preventing the required transverse restriction for polarization.This…

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Correct answer: They are longitudinal waves

424. A 16 cm long image of an object is formed by a convex lens on a screen placed normal to its principal axis. On moving the lens towards the screen, without changing the positions of the object and the screen, a 9 cm long image is formed again on the screen. The size of the object is:

  • A. 9 cm
  • B. 11 cm
  • C. 12 cm
  • D. 13 cm.

Explanation: When the lens is moved towards the screen, the height of the image formed decreases.

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Correct answer: 12 cm

425. Let x and y be the distances of the object and image formed by a concave mirror from its focus and f be the focal length, then:

  • A. xf = y2
  • B. xy = f2
  • C. x/y = f
  • D. x/y = f2

Explanation: The correct answer is Option B:xy = f2 This formula is derived from Newton's mirror relation, which states that cc' = f2 where c is the…

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Correct answer: xy = f2

426. What is the number of images of an object formed by two mirrors if the angle between the mirrors is between 2π/4 and 2π/5?

  • A. 10
  • B. 8
  • C. 6
  • D. 4

Explanation: When the angle between two mirrors falls between 2π/4 and 2π/5, the number of images formed by the mirrors is 4.

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Correct answer: 4

427. If f1 = 12 cm, f2 = -18 cm, find the maximum focal length of the combination.

  • A. 36 cm
  • B. 34 cm
  • C. 32 cm
  • D. 30 cm

Explanation: To find the maximum focal length of the combination, we use the formula 1/f = 1/f1 + 1/f2.

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Correct answer: 36 cm

428. Convex lens of 10 cm focal length is combined with a concave lens of 6 cm focal length. Find the focal length of the combination.

  • A. 15 cm
  • B. - 15 cm
  • C. 30 cm
  • D. - 30 cm

Explanation: When combining lenses, the focal length of the combination is calculated using the formula 1/f = 1/f1 + 1/f2.

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Correct answer: - 15 cm

429. The focal length of a convex lens with a refractive index of 1.5 is 2 cm. The focal length of the lens, when immersed in a liquid of refractive index 1.25, will be:

  • A. 5 cm
  • B. 7.5 cm
  • C. 10 cm
  • D. 2.5 cm

Explanation: When a convex lens with a refractive index of 1.5 and a focal length of 2 cm is immersed in a liquid with a refractive index of 1.25, the…

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Correct answer: 5 cm

430. The time required for light to pass through a glass slab of 2 mm thickness is (µglass=1.5)

  • A. 10-8 s
  • B. 10-6 s
  • C. 10-11 s
  • D. None of these

Explanation: The correct answer is Option C: 10-11 s. The time required for light to pass through a glass slab of 2 mm thickness with a refractive…

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Correct answer: 10-11 s

431. If the tube length of an astronomical telescope is 105 cm and magnifying power is 20 for the normal setting, calculate the focal length of the objective.

  • A. 100 cm
  • B. 10 cm
  • C. 20 cm
  • D. 25 cm

Explanation: To calculate the focal length of the objective, we use the formula: Tube length, L = focal length of objective (fo) + focal length of…

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Correct answer: 100 cm

432. A candle flame of height 3cm is placed at a distance of 3m from a wall. How far from the wall must a concave mirror be placed so that it may form an image of the flame 9cm high on the wall:

  • A. 425cm
  • B. 300cm
  • C. 450cm
  • D. 650cm

Explanation: To solve this problem, we use the mirror formula: 1/f = 1/v + 1/u, where f is the focal length, v is the image distance, and u is the…

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Correct answer: 450cm

433. A thin rod of length f/3 lies along the axis of a concave mirror of focal length f. One end of its magnified image touches an end of the rod. The length of the image is:

  • A. f
  • B. 1/2f
  • C. 2f
  • D. 1/4f

Explanation: When one end of the rod touches the magnified image, it is located at the center of curvature.

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Correct answer: 1/2f

434. An object is placed in front of a convex mirror at a distance of 50cm. A plane mirror is introduced covering the lower half of the convex mirror. If the distance between the object and the plane mirror is 30cm, it is found that the images formed by the two mirrors are along the same line. The radius of curvature of the mirror will be:

  • A. 12.5cm
  • B. 25cm
  • C. 50/3cm
  • D. 18cm

Explanation: When a plane mirror is introduced covering the lower half of a convex mirror, the image formed by the plane mirror is along the same line…

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Correct answer: 25cm

435. A beam of light consisting of red, green and blue colour is incident on a right-angled prism. The refractive indices of the material of the prism for the above red, green and blue wavelength are 1.39, 1.44 and 1.47 respectively. The prism will:

  • A. Separate part of red colour from the green and the blue colour
  • B. Separate part of the blue colour from the red and green colour
  • C. Separate all the colours from one another
  • D. Not separate even partially any colour from the other two colours

Explanation: A prism disperses light into its constituent colors due to varying refractive indices for each wavelength.

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Correct answer: Separate part of red colour from the green and the blue colour

436. The figure given below shows a beam of light converging at point P. When a covex lens of focal length 16cm is introduced in the path of the beam at a place O shown by a dotted line such that OP becomes the axis of the lens, the beam converges at a distance x from the lens. The value x will be equal to:

  • A. 12cm
  • B. 24/3cm
  • C. 36/5cm
  • D. 48/7cm

Explanation: When a convex lens of focal length 16cm is introduced into the path of the converging beam of light, the beam converges at a distance x…

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Correct answer: 48/7cm

437. An air bubble in a glass sphere having a 4cm diameter appears 1cm from the surface nearest to the eye when looked along the diameter. If µg = 1.5, the distance of the bubble from the refracting surface is:

  • A. 1.2cm
  • B. 3.2cm
  • C. 2.8cm
  • D. 1.6cm

Explanation: The correct distance of the bubble from the refracting surface is 1.2cm.

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Correct answer: 1.2cm

438. Two point light sources are 24cm apart. At what distance from one source must a convex lens of focal length 9cm be kept in between them so that the images of both the sources are formed at the same place?

  • A. 6cm
  • B. 9cm
  • C. 12cm
  • D. 15cm

Explanation: The problem involves placing a convex lens of focal length 9cm between two point light sources that are 24cm apart such that the images of…

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Correct answer: 12cm

439. A luminous object is placed at a distance of 30cm from the convex lens of focal length 20cm. On the other side of the lens, at what distance from the lens, a convex mirror of radius of curvature 10cm must be placed to have an upright image of the object coinciding with it:

  • A. 12cm
  • B. 30cm
  • C. 50cm
  • D. 60cm

Explanation: For the image of the object to coincide with it, the image formed by the convex lens must be located at the center of curvature of the…

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Correct answer: 50cm

440. PQR is a right-angled prism with other angles as 60o and 30o. The Refractive index of the prism is 1.5. PQ has a thin layer of liquid. Light falls normally on the face PR. For total internal reflection, the maximum refractive index of the liquid is:

  • A. 1.4
  • B. 1.3
  • C. 1.2
  • D. 1.6

Explanation: For total internal reflection to occur, the refractive index of the liquid must be less than the refractive index of the prism.

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Correct answer: 1.2
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