ROUTERA

Light-Reflection and Refraction

Class 10th Science Chapter Assertion and Reason

Light-Reflection and Refraction

  • Options:
    a) Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
    b) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
    c) Assertion (A) is true, but Reason (R) is false.
    d) Assertion (A) is false, but Reason (R) is true.

Question 1

Assertion (A): The angle of incidence is always equal to the angle of reflection.
Reason (R): This is known as the law of reflection.

  • Answer: a) Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
  • Explanation: The law of reflection states that the angle of incidence is equal to the angle of reflection, which is fundamental in understanding how light behaves when it strikes a reflective surface.

Question 2

Assertion (A): A concave mirror can produce both real and virtual images.
Reason (R): The type of image produced depends on the position of the object relative to the mirror's focal point.

  • Answer: a) Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
  • Explanation: Concave mirrors can produce real images when the object is beyond the focal point and virtual images when the object is between the focal point and the mirror.

Question 3

Assertion (A): The image formed by a plane mirror is virtual and upright.
Reason (R): In a plane mirror, the rays of light do not actually converge.

  • Answer: a) Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
  • Explanation: The image in a plane mirror appears behind the mirror, and since the light rays do not converge, the image cannot be projected on a screen, making it virtual.

Question 4

Assertion (A): The focal length of a convex lens is positive.
Reason (R): Convex lenses converge light rays to a point on the opposite side of the lens.

  • Answer: a) Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
  • Explanation: The positive focal length of a convex lens indicates that it converges incoming parallel rays to a focal point on the opposite side, which is a characteristic of converging lenses.

Question 5

Assertion (A): Total internal reflection occurs when light travels from a denser medium to a rarer medium.
Reason (R): Total internal reflection can only happen when the angle of incidence exceeds the critical angle.

  • Answer: a) Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
  • Explanation: Total internal reflection can only occur at the boundary between two media when light attempts to move from a denser medium (like water) to a rarer medium (like air) at an angle greater than the critical angle.

Question 6

Assertion (A): A virtual image cannot be projected on a screen.
Reason (R): Virtual images are formed by the apparent divergence of light rays.

  • Answer: a) Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
  • Explanation: Since virtual images are formed by rays that do not actually meet, they cannot be captured on a screen, making them only observable in the mirror or lens.

Question 7

Assertion (A): When light passes from air into water, it slows down and bends towards the normal.
Reason (R): Light travels faster in water than in air.

  • Answer: b) Assertion (A) is true, but Reason (R) is false.
  • Explanation: When light travels from a less dense medium (air) to a denser medium (water), it slows down and bends towards the normal. The statement in Reason (R) is incorrect because light travels slower in water than in air.

Question 8

Assertion (A): The refractive index of a medium is defined as the ratio of the speed of light in a vacuum to the speed of light in that medium.
Reason (R): A higher refractive index indicates that light travels slower in that medium.

  • Answer: a) Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
  • Explanation: The refractive index is a measure of how much light slows down in a medium compared to its speed in a vacuum. A higher refractive index means a lower speed of light in that medium.

Question 9

Assertion (A): A concave lens always produces virtual images.
Reason (R): Concave lenses diverge light rays.

  • Answer: a) Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
  • Explanation: Concave lenses cause parallel rays to diverge, making it appear as though they come from a virtual focal point, resulting in virtual images for all object placements.

Question 10

Assertion (A): The critical angle is the angle of incidence above which total internal reflection occurs.
Reason (R): The critical angle is specific to each pair of media.

  • Answer: a) Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
  • Explanation: The critical angle varies depending on the refractive indices of the two media involved; it is the minimum angle of incidence for which light can be totally internally reflected.

Question 11

Assertion (A): Refraction of light occurs when light passes through different media.
Reason (R): The change in speed of light in different media causes refraction.

  • Answer: a) Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
  • Explanation: As light enters a medium with a different density, its speed changes, leading to bending of light rays, which is called refraction.

Question 12

Assertion (A): A convex lens can magnify objects.
Reason (R): A convex lens has a converging effect on light rays.

  • Answer: a) Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
  • Explanation: Because a convex lens converges light rays, it can form enlarged images of objects, which is utilized in magnifying glasses and microscopes.

Question 13

Assertion (A): The laws of reflection apply to all types of surfaces.
Reason (R): The surface of a mirror is smooth, allowing for perfect reflection.

  • Answer: b) Assertion (A) is true, but Reason (R) is false.
  • Explanation: While the laws of reflection apply generally, they are most observable on smooth surfaces. Rough surfaces scatter light and do not reflect it uniformly.

Question 14

Assertion (A): When light travels from a denser medium to a rarer medium, it bends away from the normal.
Reason (R): This behavior is due to the speed of light increasing in the rarer medium.

  • Answer: a) Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
  • Explanation: When light moves from a denser to a rarer medium, it speeds up, resulting in a change in direction away from the normal line.

Question 15

Assertion (A): The image produced by a convex mirror is always virtual.
Reason (R): The focal point of a convex mirror is behind the mirror.

  • Answer: a) Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
  • Explanation: In a convex mirror, the focal point lies behind the mirror, which causes all incident light rays to diverge, leading to virtual image formation.

Question 16

Assertion (A): A ray of light passing through the optical center of a lens is unaffected by the lens.
Reason (R): The optical center is the point where the lens's curvature is symmetrical.

  • Answer: a) Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
  • Explanation: Rays passing through the optical center of a lens do not refract because they hit the lens at its most symmetric point, maintaining their original path.

Question 17

Assertion (A): The speed of light is slower in glass than in air.
Reason (R): The refractive index of glass is greater than that of air.

  • Answer: a) Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
  • Explanation: A higher refractive index indicates that light travels more slowly in that medium, making the speed of light in glass less than in air.

Question 18

Assertion (A): Dispersion of light occurs when white light passes through a prism.
Reason (R): Different colors of light travel at different speeds in glass.

  • Answer: a) Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
  • Explanation: As white light enters the prism, different wavelengths are refracted at different angles, resulting in the spectrum of colors, known as dispersion.

Question 19

Assertion (A): The ability of a lens to converge or diverge light rays is measured by its power.
Reason (R): The power of a lens is the reciprocal of its focal length measured in meters.

  • Answer: a) Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
  • Explanation: The power of a lens, expressed in diopters, is calculated as P=1fP = \frac{1}{f}, where ff is the focal length in meters. A shorter focal length indicates a stronger lens.

Question 20

Assertion (A): A light ray that strikes a boundary at an angle of 90 degrees is not refracted.
Reason (R): The angle of incidence is zero at this angle.

  • Answer: a) Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
  • Explanation: When a light ray strikes a boundary at 90 degrees (perpendicular), it continues in its original direction without bending, as the angle of incidence is zero.