### 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 angle of incidence is given as 30 degrees. 3. **Applying the Law of Reflection**: - According to the Law of Reflection: \[ \text{Angle of Incidence} = \text{Angle of Reflection} \] - Therefore, if the angle of incidence is 30 degrees, the angle of reflection must also be 30 degrees. 4. **Conclusion**: - Thus, when the beam of light strikes the flat mirror at an angle of 30 degrees to the normal, the angle of reflection is also 30 degrees. ### Why Other Options Are Incorrect: - **Option B: 45 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: 60 degrees**: - Similar to option B, this option incorrectly states that the angle of reflection is greater than the angle of incidence. The Law of Reflection clearly states that these angles must be equal. - **Option D: 90 degrees**: - This option implies that the light reflects back at a right angle to the normal. This is not possible when the angle of incidence is only 30 degrees. The angle of reflection cannot exceed the angle of incidence. ### Common Pitfalls: - **Confusing Angles**: Students often confuse the angle of incidence with the angle of reflection. Remember, they are always equal. - **Misunderstanding the Normal**: The normal line is crucial for measuring angles. It is always perpendicular to the surface at the point of incidence. - **Ignoring the Law of Reflection**: Always apply the Law of Reflection when dealing with mirrors and reflective surfaces. ### 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. - Always measure angles with respect to the normal line, not the surface. - Remember that the angles cannot exceed 90 degrees in typical reflection scenarios.