### Correct Option: A. 30 degrees ### Detailed Explanation: When light strikes a surface, such as a flat mirror, it follows a fundamental principle known as the law of reflection. This law states that the angle of incidence is equal to the angle of reflection. 1. **Understanding the Terms**: - **Angle of Incidence (i)**: This is the angle formed between the incoming light ray and the normal (an imaginary line perpendicular to the surface at the point of incidence). - **Angle of Reflection (r)**: This is the angle formed between the reflected light ray and the normal. 2. **Applying the Law of Reflection**: - According to the law of reflection: \[ \text{Angle of Incidence (i)} = \text{Angle of Reflection (r)} \] - In this case, the problem states that the beam of light strikes the mirror at an angle of 30 degrees to the normal. Therefore, we can denote: \[ i = 30^\circ \] - By the law of reflection, we can conclude: \[ r = i = 30^\circ \] 3. **Conclusion**: - Since the angle of incidence is 30 degrees, the angle of reflection is also 30 degrees. Thus, the correct answer is **A. 30 degrees**. ### Explanation of Other Options: - **B. 45 degrees**: This option is incorrect because it does not follow the law of reflection. If the angle of incidence were 45 degrees, then the angle of reflection would also be 45 degrees, which is not the case here. - **C. 60 degrees**: This option is also incorrect. It suggests that the angle of reflection is greater than the angle of incidence, which contradicts the law of reflection. - **D. 90 degrees**: This option is incorrect as well. An angle of 90 degrees would imply that the light is reflecting straight back along the normal, which is not the scenario described in the question. ### Common Pitfalls: - **Confusing Angle of Incidence with Angle of Reflection**: Remember that these two angles are always equal in the case of reflection. - **Misunderstanding the Normal Line**: The normal line is crucial for measuring angles of incidence and reflection. It is always perpendicular to the surface at the point of incidence. ### Revision Summary: - The angle of incidence equals the angle of reflection (Law of Reflection). - For a beam striking a mirror at 30 degrees to the normal, the angle of reflection is also 30 degrees. - Always visualize the normal line when solving reflection problems. - Ensure to differentiate between angles of incidence and reflection to avoid confusion.