The correct option is **C. The change in speed causes the light to bend at the interface between air and water.** ### Detailed Explanation: 1. **Understanding Refraction**: Refraction is the bending of light as it passes from one medium to another due to a change in its speed. When light travels from air (a less dense medium) into water (a denser medium), it slows down. This change in speed is what causes the light to bend towards the normal line, which is an imaginary line perpendicular to the surface at the point of incidence. 2. **Speed of Light in Different Media**: The speed of light in a vacuum is approximately \(3 \times 10^8\) meters per second. However, when light enters a medium like water, its speed decreases. The refractive index (\(n\)) of a medium is defined as the ratio of the speed of light in a vacuum to the speed of light in that medium: \[ n = \frac{c}{v} \] where \(c\) is the speed of light in a vacuum and \(v\) is the speed of light in the medium. For water, the refractive index is about 1.33, meaning light travels slower in water than in air. 3. **Bending Towards the Normal**: When light enters water from air, it slows down and bends towards the normal line. This bending can be quantitatively described using Snell's Law: \[ n_1 \sin(\theta_1) = n_2 \sin(\theta_2) \] where: - \(n_1\) is the refractive index of air (approximately 1), - \(\theta_1\) is the angle of incidence (the angle between the incoming light ray and the normal), - \(n_2\) is the refractive index of water (approximately 1.33), - \(\theta_2\) is the angle of refraction (the angle between the refracted ray and the normal). Since \(n_2 > n_1\), it follows that \(\sin(\theta_2) < \sin(\theta_1)\), which means \(\theta_2 < \theta_1\). Thus, the light ray bends towards the normal. ### Why Other Options Are Incorrect: - **Option A: The light changes color due to the different wavelengths in water.** - This statement is misleading. While light can change color due to dispersion (where different wavelengths bend by different amounts), the question specifically addresses the phenomenon of refraction as light enters water. Refraction itself does not cause a change in color; it is primarily about the change in speed and direction of light. - **Option B: The speed of light remains constant while its direction changes.** - This statement is incorrect because it contradicts the fundamental principle of refraction. The speed of light does not remain constant; it decreases when entering a denser medium like water. The change in speed is what causes the change in direction. - **Option D: The light reflects off the surface of the water instead of refracting.** - This statement is incorrect in the context of the question. While some light can reflect off the surface (as described by the law of reflection), the question specifically asks about refraction, which occurs when light passes into the water. Refraction and reflection are two distinct phenomena. ### Summary for Revision: - Refraction is the bending of light due to a change in speed when it passes from one medium to another. - Light slows down when entering a denser medium (like water) and bends towards the normal. - Snell's Law quantitatively describes the relationship between the angles of incidence and refraction and the refractive indices of the two media. - The correct understanding of refraction is crucial for solving problems related to optics and light behavior in different materials.