Final answer:
When headlights shine into fog, the light is reflected back by water particles, scattering the light and making it difficult to see, which is why drivers are advised to use low beam headlights or fog lights, if available, and not drive as they would normally.
Step-by-step explanation:
When your headlights shine into fog, light is reflected back by water particles. This occurs because the particles in the fog scatter the light in various directions, with a significant amount of light being reflected back towards the source—this is known as backscatter. The fog consists of colloidal-size water particles which diffuse the light, making it hard to see and causing a phenomenon called 'glare'. This effect is accentuated by the high beam headlights because they shine light directly into the fog instead of closer to the road surface as in the case of low beam headlights.
Different conditions such as reflection, refraction, or polarized light all refer to various fundamental aspects of how light interacts with materials it encounters. For instance, light can become polarized upon reflection from a surface, which changes how light is perceived when wearing polarized glasses. Additionally, light will bend towards or away from the normal depending on the comparative indexes of refraction between two mediums (like air and water). However, it's important to note that in foggy conditions, the main issue is the reflection and scattering of the light by the small water droplets.
Therefore, when driving in fog, it's best to use your vehicle's fog lights if available, or low beam headlights, and not to drive as you would normally since visibility is significantly reduced. Caution should be exercised, speed reduced, and distance from the car in front increased to account for the poorer visibility.