## Thursday, December 24, 2009

### Reﬂection of light

Reﬂection occurs when a light ray bounces oﬀ a surface.

Terminology :

Incident ray is the incoming light ray.

Reﬂected ray is the light ray moving away from the surface .

The most important characteristic of these rays is their angles in relation to the reﬂecting surface. These angles are measured with respect to the normal of the surface.

The normal is an imaginary line perpendicular to the surface.

The angle of incidence, θi is measured between the incident ray and the normal.

The angle of reﬂection, θr is measured between the reﬂected ray and the normal.

When a ray of light is reﬂected, the reﬂected ray lies in the same plane as the incident ray and the normal.

Law of Reﬂection
The Law of Reﬂection states that the angles of incidence and reﬂection are always equal and
that the reﬂected ray always lies in the plane of incidence.

When you smile into a mirror, you see your own face smiling back at you. Did you notice that;
i. the size of the image is the same as you (object)
ii. the distance of the image seem as the same distance of you from the mirror.
iii. when you move your left hand, the image will move it right hand
iv. then you image never upside down .

worked example:
Question: An incident ray strikes a smooth reﬂective surface at an angle of 33◦ to the surface normal. Calculate the angle of reﬂection.

Step 1 : Determine what is given and what is required We are given the angle between the incident ray and the surface normal. This is the angle of incidence. We are required to calculate the angle of reﬂection.

Step 2 : Determine how to approach the problem
We can use the Law of Reﬂection, which states that the angle of incidence is equal to the angle of reﬂection.

Step 3 : Calculate the angle of reﬂection We are given the angle of incidence to be 33◦. Therefore, the angle of reﬂection is also 33◦.

quiz :