### Correct Option: A. 30 degrees ### Detailed Explanation: When light strikes a surface, such as a plane 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 that is perpendicular to the surface of the mirror 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. This means that the incoming light ray makes a 30-degree angle with the normal. 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 light strikes the plane 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: 60 degrees**: - This option suggests that the angle of reflection is 60 degrees. However, this would imply that the angle of incidence is not equal to the angle of reflection, which contradicts the law of reflection. - **Option C: 15 degrees**: - This option is incorrect for the same reason as option B. It does not adhere to the law of reflection, which states that both angles must be equal. - **Option D: 45 degrees**: - Similar to the previous options, this choice incorrectly states the angle of reflection. It does not match the angle of incidence and therefore violates the law of reflection. ### Common Pitfalls: - **Confusing Angle of Incidence with Angle of Reflection**: Students sometimes mix up these two angles. Remember, they are always equal in the case of reflection. - **Misunderstanding the Normal Line**: The normal line is crucial for measuring angles. Ensure you visualize or draw the normal line when solving problems related to reflection. ### Revision Summary: - The angle of incidence equals the angle of reflection (Law of Reflection). - For a light ray striking a mirror at 30 degrees to the normal, the angle of reflection is also 30 degrees. - Always visualize the normal line to avoid confusion between angles. - Remember that all angles are measured from the normal, not the surface of the mirror.