Light waves are incident on an air-glass boundary. Some of the light waves are reflected and some are refracted in the glass. Which one of the following properties is the same for the incident wave and the refracted wave?

When light waves travel from air to glass, they undergo refraction due to a change in the speed of light between the two media [2]. According to the wave equation, speed is the product of frequency and wavelength. As light enters a denser medium like glass, its speed decreases and its wavelength decreases proportionally. However, the frequency of the light wave is determined by the source and remains constant regardless of the medium it travels through. The direction of the light wave also changes (unless incident normally) as it bends toward the normal in the glass. Brightness or intensity decreases because the incident energy is split between the reflected and refracted waves at the boundary. Therefore, frequency is the only property among the options that remains identical for both the incident and refracted waves.

Sources

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