In the ray experiment, which of the following can cause angle i not to equal angle r?

• A. Thickness of pins
• B. Thickness of mirror
• C. Protractor is not precise
• D. All of the above

Answer: (D)

In this experiment, the law of reflection says the angle of incidence equals the angle of reflection when the surface is smooth and measurements are exact. Real setups introduce small errors that can upset that equality. If the pins used to mark the light paths have thickness, the drawn incident and reflected lines can be offset from the true paths, shifting the angles you measure. A mirror that isn’t perfectly thin or has depth can change which surface the light reflects from or affect the orientation of the normal, giving a slightly different measured reflected angle. If the protractor isn’t precise, the readings themselves will be off, making i and r appear unequal. All of these factors can cause angle i not to equal angle r.