### Correct Option: B (30 degrees) ### Detailed Explanation: 1. **Understanding the Law of Reflection**: - The law of reflection states that when a beam of light strikes a reflective surface (like a flat mirror), the angle of incidence is equal to the angle of reflection. This is a fundamental principle in optics. - Mathematically, this can be expressed as: \[ \text{Angle of Incidence} = \text{Angle of Reflection} \] - Both angles are measured from the normal line, which is an imaginary line perpendicular to the surface of the mirror at the point of incidence. 2. **Identifying the Angles**: - In this problem, the angle of incidence is given as 30 degrees. According to the law of reflection, the angle of reflection must also be 30 degrees. - Therefore, when the light beam strikes the mirror at 30 degrees to the normal, it will reflect off the mirror at the same angle of 30 degrees to the normal. 3. **Visualizing the Situation**: - Imagine a flat mirror placed vertically. If you draw a line perpendicular to the mirror at the point where the light hits (this is the normal line), you can visualize the angles: - The angle of incidence (30 degrees) is the angle between the incoming light ray and the normal. - The angle of reflection (also 30 degrees) is the angle between the reflected light ray and the normal. ### Why Other Options Are Incorrect: - **Option A: 15 degrees**: - This option suggests that the angle of reflection is less 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: 45 degrees**: - This option implies that the light reflects at a much larger angle than it strikes the mirror. Again, this contradicts the law of reflection, which states that both angles must be equal. - **Option D: 60 degrees**: - Similar to option C, this option suggests a reflection angle that is greater than the angle of incidence. This is not possible according to the law of reflection. ### Common Pitfalls: - **Misunderstanding the Normal Line**: Students sometimes forget that angles are measured from the normal line, not from the surface of the mirror. - **Confusing Incidence and Reflection**: It’s crucial to remember that the angle of incidence and the angle of reflection are always equal; mixing them up can lead to incorrect answers. ### Revision Summary: - The angle of incidence equals the angle of reflection (Law of Reflection). - Both angles are measured from the normal line to the surface of the mirror. - In this case, with an angle of incidence of 30 degrees, the angle of reflection is also 30 degrees. - Always visualize the situation with a diagram to avoid common mistakes.