### Correct Option: A. 30 degrees ### Detailed Explanation: 1. **Understanding the Law of Reflection**: The law of reflection states that when a light ray strikes a reflective surface (like a flat mirror), the angle of incidence is equal to the angle of reflection. This law can be expressed mathematically as: \[ \theta_i = \theta_r \] where: - \(\theta_i\) is the angle of incidence (the angle between the incoming light ray and the normal to the surface), - \(\theta_r\) is the angle of reflection (the angle between the reflected light ray and the normal). 2. **Identifying the Angles**: In this problem, the beam of light strikes the mirror at an angle of 30 degrees with respect to the normal. This means: - \(\theta_i = 30^\circ\) 3. **Applying the Law of Reflection**: According to the law of reflection, since the angle of incidence is 30 degrees, the angle of reflection must also be: \[ \theta_r = 30^\circ \] 4. **Conclusion**: Therefore, the angle of reflection when the beam of light strikes the flat mirror at an angle of 30 degrees with respect to the normal is also 30 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, the angle of reflection cannot be 45 degrees. - **Option C: 60 degrees**: Similar to option B, this option incorrectly states that the angle of reflection is 60 degrees. Again, this does not comply with the law of reflection, as the angle of reflection must match the angle of incidence, which is 30 degrees. - **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 the case here. The angle of incidence is 30 degrees, so the angle of reflection cannot be 90 degrees. ### Common Pitfalls: - **Confusing Angle of Incidence with Angle of Reflection**: It's crucial to remember that these two angles are equal according to the law of reflection. - **Misunderstanding the Normal Line**: The normal line is an imaginary line perpendicular to the surface at the point of incidence. Always measure angles with respect to this line, not the surface itself. ### Revision Summary: - The angle of incidence equals the angle of reflection (Law of Reflection). - In this case, both angles are 30 degrees. - Always measure angles with respect to the normal line, not the surface. - Remember that any deviation from the law of reflection indicates a misunderstanding of the basic principles of optics.