Understanding Angle of Incidence and Reflection
When a ray of light strikes a surface, it undergoes reflection. The angle at which the incoming ray hits the surface is termed the angle of incidence, while the angle at which it reflects off the surface is known as the angle of reflection.
Key Concepts:
- The Law of Reflection states that the angle of incidence is equal to the angle of reflection.
- Both angles are measured with respect to the normal (an imaginary line perpendicular to the surface at the point of incidence).
Scenario Explanation:
If the reflected ray is at an angle of 90° to the incident ray, we can analyze the situation as follows:
- Let’s denote the angle of incidence as "i" and the angle of reflection as "r".
- According to the law of reflection: i = r.
- If the reflected ray is at 90° to the incident ray, we can visualize this setup as follows:
- The incident ray and the reflected ray form a straight line when combined with the normal.
Calculating the Angles:
- The total angle formed by the incident ray and the reflected ray is 90°.
- Thus, if we denote the angle between the incident ray and the normal as i, and between the reflected ray and the normal also as r, we can infer:
- i + r = 90°.
- Since i = r, we can substitute to get: 2i = 90°.
- Therefore, the angle of incidence (i) is 45°.
Conclusion:
In this case, the angle of incidence is 45°, ensuring that the reflected ray is at a perfect 90° angle to the incident ray. Understanding these relationships is crucial in optics and helps explain how light behaves when interacting with different surfaces.

Angle of incidence will be 90.
because according to law Angle if reflection is equal to Angle of reflection.
So, if angle of reflection is 90 so angle of incidence is 90.