### 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 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 formed 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 case, the problem states that the beam of light strikes the mirror at an angle of 30 degrees to the normal. Therefore, we can denote: \[ i = 30^\circ \] - By the law of reflection, we can conclude: \[ r = i = 30^\circ \] 3. **Conclusion**: - The angle of reflection is also 30 degrees. Thus, the correct answer is **A. 30 degrees**. ### Explanation of Other Options: - **B. 60 degrees**: This option is incorrect because it suggests that the angle of reflection is greater than the angle of incidence. According to the law of reflection, this cannot happen; the angles must be equal. - **C. 90 degrees**: This option is also incorrect. An angle of 90 degrees would imply that the light is reflecting straight back along the normal, which is not the case here. The angle of incidence is only 30 degrees. - **D. 45 degrees**: This option is incorrect for the same reason as the others. It does not adhere to the law of reflection, which states that the angle of reflection must equal the angle of incidence. ### Common Pitfalls: - **Confusing the Angle with the Normal**: Students often confuse the angle of incidence with the angle relative to the surface of the mirror. Remember, the angles are measured from the normal, not the surface. - **Misapplying the Law of Reflection**: It’s crucial to remember that the law states the angles are equal. If you find yourself calculating different angles, double-check your understanding of the law. ### Revision Summary: - The angle of incidence equals the angle of reflection (Law of Reflection). - For a beam striking a mirror at 30 degrees to the normal, the angle of reflection is also 30 degrees. - Always measure angles from the normal, not the surface. - Review the definitions of angle of incidence and angle of reflection to avoid confusion.