### 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 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 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 problem, the angle of incidence is given as 30 degrees. 3. **Calculating the Angle of Reflection**: - Since the angle of incidence is 30 degrees, we can directly apply the law of reflection: \[ r = i = 30 \text{ degrees} \] - Therefore, the angle of reflection is also 30 degrees. ### Why the Other Options Are Incorrect: - **Option B: 60 degrees**: - This option suggests that the angle of reflection is greater than the angle of incidence. According to the law of reflection, this is incorrect because the angle of reflection must equal the angle of incidence. - **Option C: 90 degrees**: - This option implies that the light is reflecting off the mirror at a right angle. This would only occur if the angle of incidence were 90 degrees, which is not the case here. The angle of incidence is 30 degrees, so this option is incorrect. - **Option D: 15 degrees**: - This option suggests a much smaller angle of reflection than the angle of incidence. Again, this contradicts the law of reflection, which states that the angles must be equal. Therefore, this option is also incorrect. ### 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. It is always perpendicular to the surface at the point of incidence. - **Forgetting the Law of Reflection**: Always recall that the law of reflection applies to all types of reflection, including flat mirrors. ### Revision Summary: - The angle of incidence equals the angle of reflection (Law of Reflection). - For a flat mirror, if the angle of incidence is 30 degrees, the angle of reflection is also 30 degrees. - Always measure angles with respect to the normal line, not the surface of the mirror. - Remember that the law of reflection applies universally to all reflective surfaces.