Human Eye and the Colourful World

  1. Assertion (A): A convex lens is used to correct hypermetropia.
    Reason (R): Hypermetropia occurs when the image of nearby objects is formed behind the retina.
    Answer: Both A and R are true, and R is the correct explanation of A.
    Explanation: Convex lenses help focus images onto the retina in hypermetropic eyes.
  2. Assertion (A): A concave lens is used to correct myopia.
    Reason (R): Myopia occurs when the image of distant objects is formed in front of the retina.
    Answer: Both A and R are true, and R is the correct explanation of A.
    Explanation: Concave lenses help adjust the focal point for distant vision in myopic eyes.
  3. Assertion (A): The power of a lens is the reciprocal of its focal length.
    Reason (R): The SI unit of power of a lens is dioptre.
    Answer: Both A and R are true, but R is not the correct explanation of A.
    Explanation: Power is indeed the reciprocal of focal length, and its SI unit is dioptre.
  4. Assertion (A): The focal length of a lens increases when it is placed in water.
    Reason (R): The refractive index of water is less than that of air.
    Answer: A is true, but R is false.
    Explanation: The focal length increases in water due to a lower refractive index contrast, not because water’s refractive index is less than air.
  5. Assertion (A): A ray passing through the optical center of a lens does not bend.
    Reason (R): The optical center is the point on the lens where light rays pass undeviated.
    Answer: Both A and R are true, and R is the correct explanation of A.
    Explanation: Rays passing through the optical center are undeviated because the lens has no curvature at that point.
  6. Assertion (A): A rainbow is formed due to dispersion, refraction, and reflection of light in water droplets.
    Reason (R): The light rays are internally reflected inside the water droplets and then refracted.
    Answer: Both A and R are true, and R is the correct explanation of A.
    Explanation: Rainbow formation involves dispersion, refraction, and internal reflection of light in water droplets.
  7. Assertion (A): Blue light is scattered more than red light in the atmosphere.
    Reason (R): Scattering of light is inversely proportional to the fourth power of the wavelength.
    Answer: Both A and R are true, and R is the correct explanation of A.
    Explanation: Shorter wavelengths (like blue) are scattered more than longer wavelengths (like red).
  8. Assertion (A): The sky appears blue because blue light is scattered more than red light.
    Reason (R): Blue light has a shorter wavelength than red light.
    Answer: Both A and R are true, and R is the correct explanation of A.
    Explanation: The shorter wavelength of blue light leads to greater scattering, causing the sky to appear blue.
  9. Assertion (A): The white color of clouds is due to scattering of light.
    Reason (R): Large water droplets scatter all wavelengths of light almost equally.
    Answer: Both A and R are true, and R is the correct explanation of A.
    Explanation: Large water droplets scatter all colors equally, making clouds appear white.
  10. Assertion (A): Light bends when it passes from one medium to another.
    Reason (R): Refraction occurs due to a change in the speed of light in different media.
    Answer: Both A and R are true, and R is the correct explanation of A.
    Explanation: Refraction happens because light travels at different speeds in different media.
  11. Assertion (A): The dispersion of light occurs because different colors of light travel at different speeds in a medium.
    Reason (R): Violet light bends more than red light as it has a shorter wavelength.
    Answer: Both A and R are true, and R is the correct explanation of A.
    Explanation: The varying speeds of colors in a medium lead to dispersion, with violet bending more due to its shorter wavelength.
  12. Assertion (A): A prism can separate white light into its constituent colors.
    Reason (R): The refractive index of a material varies with the wavelength of light passing through it.
    Answer: Both A and R are true, and R is the correct explanation of A.
    Explanation: The variation of refractive index with wavelength causes dispersion in a prism, separating white light.
  13. Assertion (A): Red light is refracted less than blue light in a prism.
    Reason (R): The refractive index for red light is lower than for blue light.
    Answer: Both A and R are true, and R is the correct explanation of A.
    Explanation: Red light has a longer wavelength and is refracted less than blue light due to its lower refractive index.
  14. Assertion (A): Convex lenses converge parallel rays of light to a focal point.
    Reason (R): Convex lenses have a positive focal length.
    Answer: Both A and R are true, but R is not the correct explanation of A.
    Explanation: Convex lenses converge light due to their shape, not simply because of their positive focal length.
  15. Assertion (A): Concave lenses are used in cameras to focus light.
    Reason (R): Concave lenses diverge light rays.
    Answer: A is false, but R is true.
    Explanation: Cameras use convex lenses to focus light; concave lenses are used to diverge light, not for focusing.
  16. Assertion (A): The size of an image formed by a concave mirror decreases as the object moves away from the mirror.
    Reason (R): The magnification of a concave mirror decreases as the object distance increases.
    Answer: Both A and R are true, and R is the correct explanation of A.
    Explanation: As the object distance increases, the image size reduces in a concave mirror due to decreasing magnification.
  17. Assertion (A): The far point of a myopic eye is closer than infinity.
    Reason (R): Myopia is a defect of vision in which the eye can see nearby objects clearly, but distant objects appear blurry.
    Answer: Both A and R are true, and R is the correct explanation of A.
    Explanation: Myopic eyes have a far point closer than infinity, which is why distant objects are blurry.
  18. Assertion (A): The human eye can see objects clearly in dim light due to the presence of rods.
    Reason (R): Rods are light-sensitive cells responsible for vision in low-light conditions.
    Answer: Both A and R are true, and R is the correct explanation of A.
    Explanation: Rod cells in the retina are responsible for vision in low-light conditions.
  19. Assertion (A): Short-sightedness can be corrected using a concave lens.
    Reason (R): A concave lens diverges light rays before they enter the eye, helping to focus the image on the retina.
    Answer: Both A and R are true, and R is the correct explanation of A.
    Explanation: Concave lenses correct myopia by diverging light rays, allowing them to focus on the retina.
  20. Assertion (A): Bifocal lenses are used to correct presbyopia.
    Reason (R): Presbyopia is a condition where the eye loses its ability to focus on nearby objects.
    Answer: Both A and R are true, and R is the correct explanation of A.
    Explanation: Bifocal lenses help correct presbyopia by providing two focal lengths for near and distant vision.