### Correct Option: B. The speed decreases and it bends towards the normal. #### Detailed Explanation: When light travels from one medium to another, such as from air (a less dense medium) into water (a denser medium), two key phenomena occur: a change in speed and a change in direction (refraction). 1. **Change in Speed**: - Light travels at different speeds in different media. In a vacuum, light travels at its maximum speed, approximately \(3 \times 10^8\) meters per second. However, when light enters a denser medium like water, its speed decreases. The speed of light in water is about \(2.25 \times 10^8\) meters per second. - This decrease in speed occurs because the molecules in water are closer together than in air, causing the light waves to interact more with the water molecules, which slows them down. 2. **Change in Direction (Refraction)**: - When light enters a new medium at an angle, it changes direction. This bending of light is described by Snell's Law, which states: \[ n_1 \sin(\theta_1) = n_2 \sin(\theta_2) \] where: - \(n_1\) is the refractive index of the first medium (air, approximately 1.00), - \(n_2\) is the refractive index of the second medium (water, approximately 1.33), - \(\theta_1\) is the angle of incidence (the angle between the incoming light ray and the normal), - \(\theta_2\) is the angle of refraction (the angle between the refracted ray and the normal). - Since the refractive index of water is greater than that of air, when light enters water from air, it bends towards the normal line (an imaginary line perpendicular to the surface at the point of incidence). This means that the angle of refraction (\(\theta_2\)) is smaller than the angle of incidence (\(\theta_1\)). #### Why Other Options Are Incorrect: - **Option A: The speed increases and it bends away from the normal.** - This option is incorrect because the speed of light decreases when it enters a denser medium like water. Additionally, light bends towards the normal, not away from it. - **Option C: The speed remains constant and it travels in a straight line.** - This option is incorrect because the speed of light does not remain constant when transitioning between media. It also does not travel in a straight line; it bends due to refraction. - **Option D: The speed decreases and it bends away from the normal.** - While this option correctly states that the speed decreases, it incorrectly states that the light bends away from the normal. In fact, light bends towards the normal when entering a denser medium. ### Summary of Key Points: - Light slows down when entering a denser medium (from air to water). - Light bends towards the normal when it enters a denser medium. - Snell's Law describes the relationship between the angles of incidence and refraction and the refractive indices of the two media. - Understanding the behavior of light at the interface of different media is crucial for applications in optics and various technologies.