Kerala SSLC · Physics · Class 10

Light – Refraction: Important Questions with Answers

These are 10 important multiple-choice questions from the Kerala SSLC Physics chapter “Light – Refraction” (Kerala SCERT syllabus). Each one shows the correct answer and a short explanation of why it is right. Try answering before you read the answer. ExamSummary has 10 practice questions on this chapter in total.

  1. Q1.When a ray of light travels from air into water, how does it bend relative to the normal?

    • A)It bends towards the normal
    • B)It bends away from the normal
    • C)It continues without bending
    • D)It reflects back into the air

    Answer: A) It bends towards the normal

    Water is optically denser than air. According to the laws of refraction, when light enters a denser medium from a rarer medium, its speed decreases, causing it to bend towards the normal.

  2. Q2.What is the absolute refractive index of a medium defined as?

    • A)The ratio of the speed of light in the medium to the speed of light in vacuum
    • B)The ratio of the speed of light in vacuum to the speed of light in the medium
    • C)The product of the speed of light in vacuum and the medium
    • D)The difference between the speed of light in vacuum and the medium

    Answer: B) The ratio of the speed of light in vacuum to the speed of light in the medium

    The absolute refractive index (n) is mathematically defined as n = c/v, where c is the speed of light in vacuum and v is the speed of light in the specific medium.

  3. Q3.If an object is placed exactly at the principal focus of a convex lens, where will the image be formed?

    • A)At the center of curvature
    • B)At infinity
    • C)Between the focus and the optical center
    • D)At the focus itself

    Answer: B) At infinity

    When an object is placed at the principal focus of a convex lens, the refracted rays emerge parallel to the principal axis and meet at infinity, forming an image at infinity.

  4. Q4.What is the SI unit used to measure the power of a lens?

    • A)Meter
    • B)Centimeter
    • C)Dioptre
    • D)Joule

    Answer: C) Dioptre

    The power of a lens is the reciprocal of its focal length measured in meters. The SI unit for this quantity is the Dioptre (D).

  5. Q5.Which of the following best describes the image formed by a concave lens for any position of the object?

    • A)Real, inverted, and magnified
    • B)Virtual, erect, and diminished
    • C)Real, erect, and same size
    • D)Virtual, inverted, and magnified

    Answer: B) Virtual, erect, and diminished

    A concave lens is a diverging lens. Regardless of where the object is placed, it always forms a virtual, erect, and diminished image on the same side as the object.

  6. Q6.Calculate the power of a convex lens having a focal length of 50 cm.

    • A)+2 Dioptre
    • B)-2 Dioptre
    • C)+5 Dioptre
    • D)-5 Dioptre

    Answer: A) +2 Dioptre

    First convert focal length to meters: 50 cm = 0.5 m. Power P = 1/f(m). So, P = 1/0.5 = +2 D. The positive sign indicates a convex lens.

  7. Q7.How is the refractive index related to the real depth and apparent depth of an object submerged in water?

    • A)n = Apparent Depth / Real Depth
    • B)n = Real Depth + Apparent Depth
    • C)n = Real Depth / Apparent Depth
    • D)n = Apparent Depth - Real Depth

    Answer: C) n = Real Depth / Apparent Depth

    The refractive index is equal to the ratio of the real depth to the apparent depth. This explains why a swimming pool appears shallower than it actually is.

  8. Q8.A ray of light passes through a rectangular glass slab. What is the relationship between the incident ray and the emergent ray?

    • A)They are perpendicular to each other
    • B)They are parallel to each other
    • C)They converge at a point
    • D)They diverge from each other

    Answer: B) They are parallel to each other

    Due to the parallel surfaces of the glass slab, the emergent ray is parallel to the incident ray, though there is a slight lateral displacement between them.

  9. Q9.Why do stars appear to twinkle when viewed from Earth?

    • A)Because they emit fluctuating light
    • B)Due to atmospheric refraction
    • C)Due to total internal reflection
    • D)Due to scattering by dust particles

    Answer: B) Due to atmospheric refraction

    Twinkling occurs because starlight undergoes continuous refraction while passing through layers of the atmosphere with varying densities, causing the apparent position to fluctuate.

  10. Q10.In the lens formula (1/v - 1/u = 1/f), what does the symbol 'f' represent?

    • A)Distance of the object from the lens
    • B)Distance of the image from the lens
    • C)Focal length of the lens
    • D)Radius of curvature of the lens

    Answer: C) Focal length of the lens

    In the standard lens formula, 'u' represents object distance, 'v' represents image distance, and 'f' represents the focal length of the lens.

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