### 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 ray of light 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 ray of light 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 angle of incidence is given as 30 degrees. Therefore, we can directly apply the law: \[ r = i = 30 \text{ degrees} \] 3. **Conclusion**: - Since the angle of incidence is 30 degrees, the angle of reflection is also 30 degrees. Thus, the correct answer is option A. ### Why Other Options Are Incorrect: - **Option B: 45 degrees**: - This option suggests that the angle of reflection is 45 degrees. However, this contradicts the law of reflection, which states that the angle of incidence must equal the angle of reflection. Since the angle of incidence is 30 degrees, this option is incorrect. - **Option C: 60 degrees**: - Similar to option B, this option incorrectly states that the angle of reflection is 60 degrees. Again, this does not adhere to the law of reflection, making it an incorrect choice. - **Option D: 90 degrees**: - This option implies that the angle of reflection is 90 degrees. This would mean that the light is reflecting straight back along the normal, which is not the case here. The angle of incidence is only 30 degrees, so this option is also incorrect. ### Common Pitfalls: - **Confusing Angle of Incidence with Angle of Reflection**: Students often mix up these two angles. Remember, they are always equal according to the law of reflection. - **Misunderstanding the Normal Line**: The normal line is crucial for measuring angles. It is always perpendicular to the surface at the point of incidence. - **Forgetting the Law of Reflection**: Always recall that the angle of incidence equals the angle of reflection when dealing with mirrors. ### Revision Summary: - The angle of incidence equals the angle of reflection (law of reflection). - For a beam striking a mirror at 30 degrees, the angle of reflection is also 30 degrees. - Options that suggest different angles (45, 60, 90 degrees) violate the law of reflection. - Always visualize the normal line to accurately measure angles in reflection problems.