### Correct Option: A. The light slows down and bends towards the normal. #### Detailed Explanation: When light travels from one medium to another, its speed and direction can change due to the different optical densities of the materials involved. In this case, we are considering the transition of light from air (a less dense medium) into water (a denser medium). 1. **Speed of Light in Different Media**: - The speed of light in a vacuum is approximately \(3.00 \times 10^8\) meters per second. - In air, the speed of light is very close to this value, but it is slightly less due to the presence of air molecules. - In water, the speed of light is significantly reduced to about \(2.25 \times 10^8\) meters per second. This reduction in speed occurs because light interacts with the water molecules, which causes it to take longer to travel through the medium. 2. **Refraction and the Normal Line**: - When light enters a new medium at an angle, it bends. This bending of light is called refraction. - The "normal" line is an imaginary line that is perpendicular to the surface at the point of incidence (where the light hits the water). - When light moves from a less dense medium (air) to a more dense medium (water), it bends towards the normal line. This is due to the change in speed; as the light slows down, it changes direction. 3. **Understanding the Change in Direction**: - According to Snell's Law, which describes how light refracts, the relationship between the angles of incidence and refraction is given by: \[ n_1 \sin(\theta_1) = n_2 \sin(\theta_2) \] 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, the sine of the angle of refraction will be less than the sine of the angle of incidence, indicating that \(\theta_2 < \theta_1\). This confirms that the light bends towards the normal. #### Why Other Options Are Incorrect: - **Option B: The light speeds up and bends away from the normal.** - This option is incorrect because when light enters a denser medium (like water), it actually slows down, not speeds up. Additionally, light bends towards the normal when entering a denser medium, not away from it. - **Option C: The light speeds up and continues in a straight line.** - This option is also incorrect because the light does not speed up when entering water; it slows down. Furthermore, light does not continue in a straight line when it crosses the boundary between two different media; it refracts. - **Option D: The light slows down and continues in a straight line.** - This option is misleading. While it is true that the light slows down when entering water, it does not continue in a straight line. Instead, it bends towards the normal due to the change in speed. ### Summary for Revision: - Light slows down when moving from air (less dense) to water (more dense). - Light bends towards the normal line when entering a denser medium. - Snell's Law describes the relationship between angles of incidence and refraction. - Remember: denser medium = slower speed of light and bending towards the normal.