Which of the following statements is/are true regarding a light wave travelling from air to glass? 1. Its frequency remains unchanged. 2. Its speed changes. Select the correct answer using the code given below :

When a light wave travels from air to glass, it undergoes refraction due to the change in the optical density of the medium. According to the principles of wave physics, the frequency of a light wave is determined solely by its source and remains constant regardless of the medium it passes through [t1, t2]. Therefore, statement 1 is correct. However, the speed of light is dependent on the refractive index of the medium. Light travels at approximately 3 × 10⁸ m/s in a vacuum or air, but its speed reduces significantly when entering a denser medium like glass [c1, c2]. This change in speed is the fundamental cause of refraction [c3]. Since both the frequency remains unchanged and the speed changes (decreases), both statements 1 and 2 are true. This relationship is governed by the equation v = fλ, where a decrease in speed (v) results in a proportional decrease in wavelength (λ) while frequency (f) stays constant [t1, t3].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 9: Light – Reflection and Refraction > What you have learnt > p. 159
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 9: Light – Reflection and Refraction > 9.3.2 The Refractive Index > p. 148
3. [3] Science , class X (NCERT 2025 ed.) > Chapter 9: Light – Reflection and Refraction > Activity 9.10 > p. 147