iGCSE Physics (0625) 3.2.1 Reflection of light-Exam Style Questions- New Syllabus
▶️ Answer/Explanation
Detailed solution:
According to the law of reflection, for any ray of light striking a plane mirror, the angle of incidence i is equal to the angle of reflection r, measured from the normal.
In the provided diagram, the dashed lines perpendicular to the mirror surface represent the normals at the points of incidence.
For the first ray, angle 1 is the angle of incidence and angle 2 is the angle of reflection, therefore angle 1=angle 2.
For the second ray, angle 3 is the angle of incidence and angle 4 is the angle of reflection, therefore angle 3=angle 4.
Since each individual reflection must independently obey this law, the only correct relationship is found in option A.
▶️ Answer/Explanation
Detailed solution:
In a plane mirror, the image is the same distance behind the mirror as the object is in front of it. Since the droplet is $1.5 \text{ m}$ above the mirror, the image is $1.5 \text{ m}$ below it, making the total distance $1.5 \text{ m} + 1.5 \text{ m} = 3.0 \text{ m}$. The speed of the image relative to the mirror is identical to the speed of the object relative to the mirror, which is $2.0 \text{ m/s}$. While the relative speed between the droplet and image is $4.0 \text{ m/s}$, the question asks for the “speed of the image,” which is measured relative to the mirror. Thus, the correct values are $3.0 \text{ m}$ and $2.0 \text{ m/s}$.
▶️ Answer/Explanation
Detailed solution:
The normal is an imaginary line perpendicular to the mirror surface, forming a 90° angle.
The angle of incidence i is measured between the incident ray and the normal, not the mirror surface.
Given the angle between the ray and the surface is 35°, the angle of incidence is 90 ∘ −35 ∘ =55 ∘ .
According to the law of reflection, the angle of incidence i is equal to the angle of reflection r.
Therefore, the angle of reflection is also 55 ∘ , making option B the only correct statement.