### 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 Angles**: - The **angle of incidence** is the angle between the incoming light ray and the normal (an imaginary line perpendicular to the surface at the point of incidence). - The **angle of reflection** is the angle between the reflected light ray and the normal. 2. **Given Information**: - The problem states that a beam of light strikes a flat mirror at an angle of 30 degrees to the normal. This means: - Angle of incidence (i) = 30 degrees. 3. **Applying the Law of Reflection**: - According to the law of reflection: \[ \text{Angle of incidence (i)} = \text{Angle of reflection (r)} \] - Therefore, if the angle of incidence is 30 degrees, the angle of reflection must also be: \[ r = 30 \text{ degrees} \] ### 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 reflection must equal the angle of incidence. 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, which requires the angles to be equal. Therefore, this option is also incorrect. - **Option D: 90 degrees**: - This option implies that the angle of reflection is 90 degrees. This would mean that the light ray is reflecting straight back along the normal, which is not possible given that the angle of incidence is only 30 degrees. Thus, this option is incorrect as well. ### Summary of Key Concepts: - **Law of Reflection**: The angle of incidence equals the angle of reflection. - **Angle of Incidence**: The angle between the incoming ray and the normal. - **Angle of Reflection**: The angle between the reflected ray and the normal. - For a flat mirror, if the angle of incidence is 30 degrees, the angle of reflection is also 30 degrees. ### Revision Summary: - The angle of incidence equals the angle of reflection. - For a flat mirror, if light strikes at 30 degrees to the normal, the reflection is also at 30 degrees. - Incorrect options violate the law of reflection. - Always visualize the normal line to understand the angles involved in reflection.