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Q22 (NDA-II/2016) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Geometrical optics Answer Verified

When a ray of light enters a glass slab, then

Result
Your answer: —  Â·  Correct: C
Explanation

When a ray of light enters a glass slab from air, it undergoes refraction due to a change in its speed [2]. The speed of light decreases in glass because it is an optically denser medium compared to air [3]. According to the wave equation (v = fλ), the velocity (v) and wavelength (λ) are directly proportional when frequency (f) is constant. While the speed and wavelength of the light decrease upon entering the glass slab, the frequency remains unchanged. Frequency is a characteristic property of the light source and does not depend on the medium through which the light travels. Therefore, when light enters a glass slab, its frequency does not change, making option 3 the most accurate description of the invariant property during this transition.

Sources

  1. [1] Science , class X (NCERT 2025 ed.) > Chapter 9: Light – Reflection and Refraction > Activity 9.10 > p. 147
  2. [2] Science , class X (NCERT 2025 ed.) > Chapter 9: Light – Reflection and Refraction > What you have learnt > p. 159
  3. [3] Science , class X (NCERT 2025 ed.) > Chapter 9: Light – Reflection and Refraction > QUESTIONS > p. 150
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