Chapter 25, Problem 1CQ

Using the law of reflection, explain how powder takes the shine off of a person’s nose. What is the name of the optical effect?

To determine

The reason for the fact "powder takes the shine off of a person's nose" using law of reflection and state the name of the optical effect.

Answer to Problem 1CQ

No shine is observed when powder is applied on the nose because light rays are diffused when it falls on the rough surface of the nose. The optical effect is scattering of light.

Explanation of Solution

A light ray is completely reflected when it falls on smooth surface at same angle. Due to this reflection, shine is observed on that surface. This condition is based on the rule of reflection that is, "angle of reproduction is equal to angle of prevalence". A person's nose acts like smooth surface. When the rays of light fall on the person's nose, they are completely reflected at similar angles. Hence, nose shines. The following diagram reflects the above condition:

  

Figure (1)

When powder is applied on the nose, it makes the smooth surface uneven. Light rays are scattered or diffused when it reflects from the rough surface. When the parallel rays of light falls on the powdered nose, they are reflected at different angles due to the rough surface. Hence, no shine is observed in this case. The following diagram reflects the above condition:

  

Figure (2)

The optical effect is scattering of light.

Conclusion:

Thus, no shine is observed when powder is applied on the nose because light rays are diffused when it falls on the rough surface of the nose. The optical effect is scattering of light.