### 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 formed 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 formed 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 that the angle of incidence (i) is 30 degrees. 3. **Applying the Law of Reflection**: - According to the law of reflection: \[ \text{Angle of Incidence (i)} = \text{Angle of Reflection (r)} \] - Since the angle of incidence is given as 30 degrees, we can directly conclude: \[ r = 30 \text{ degrees} \] 4. **Conclusion**: - Therefore, the angle of reflection is also **30 degrees**. ### Why Other Options Are Incorrect: - **Option B: 60 degrees**: - This option suggests that the angle of reflection is 60 degrees. However, this would imply that the angle of incidence was 60 degrees, which contradicts the given information that it is 30 degrees. Thus, this option is incorrect. - **Option C: 90 degrees**: - An angle of reflection of 90 degrees would mean that the light is reflecting straight back along the path of the normal, which is not the case here. The angle of incidence is 30 degrees, so this option is also incorrect. - **Option D: 15 degrees**: - This option suggests a much smaller angle of reflection. Since the law of reflection states that the angle of incidence equals the angle of reflection, a 15-degree angle of reflection would imply a 15-degree angle of incidence, which again contradicts the given information. Therefore, this option is incorrect. ### Common Pitfalls: - **Confusing Angle of Incidence with Angle of Reflection**: Always remember that these two angles are equal according to the law 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. ### 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 visualize the normal line when dealing with angles of incidence and reflection. - Double-check the given angle to avoid confusion with the angles of reflection or incidence.