4. Define angle of inclination and angle of incidence.

**Angle of Inclination:**<br /><br />The angle of inclination refers to the angle between a line (or a plane) and the horizontal. It's essentially a measure of how steep the line or plane is. Think of it as the angle a hill makes with flat ground. It's always measured upwards from the horizontal.<br /><br />**Angle of Incidence:**<br /><br />The angle of incidence is the angle between a ray (like a light ray or a projectile's path) incident on a surface and the *normal* to that surface at the point of incidence. The normal is a line perpendicular (at a 90-degree angle) to the surface. It's important to note that the angle of incidence is *not* measured relative to the surface itself, but rather to this perpendicular line.<br />