Chapter 17, Problem 69A

To determine

To explain: The reason for a wet road to appear blacker than a dry road.

Explanation of Solution

Introduction:

When the light incident on an object gets bounced back, it is called reflection of light. If the reflecting surface is smooth then the angle at which the light gets reflected is same as that of the angle at which the light incident on that surface. But if the reflecting surface is rough then the light gets reflected in different directions. This is called diffuse reflection. Most of the objects are visible because of the reflection of light from the source (from its surface).

Consider the figure for the condition shown below.

  

Figure 1

The dry road has a rough surface and thus light gets reflected in different directions. So, a large amount of light rays are reflected back to the car. When the road is wet, water is a smoother surface like a plane mirror and hence reflects light only in particular direction. Thus, less amount of light is reflected back to the car. Therefore, wet road appears blacker than a dry road.