Optics 2: Law of Reflection

• Physics
• Secondary Education
• Age 13

Forces and Motion

Lesson 10b. 

Reflection of Light (Ray Diagram)

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Highlights of the Day

•  describe the reflection at a plane surface and use the law of reflection

• Values :  Responsibility and Determination

Did you know?

Ray Diagrams

• show what happens to the light rays during reflection
• obeys the law of reflection which states that the angle of reflection is equal to the angle of incidence

RAY DIAGRAM

STEPS IN DRAWING

Draw the incident ray and the mirror. Sometimes, this is done for you.

1

Use a ruler to make the incident ray meet the mirror.

2

Use a protractor or set square to draw the normal. The normal is <span style="color: rgb(255, 238, 0); font-weight: bold">perpendicular</span> to the mirror where the incident ray meets the surface. The normal is a<span style="font-weight: bold; color: rgb(255, 238, 0)"> dashed line</span> so it is not confused with the light ray.

3

Use a <span style="font-weight: bold; color: rgb(255, 238, 0)">protractor </span>to measure the angle between the incident ray and the normal. We call this angle, the <span style="font-weight: bold; color: rgb(255, 238, 0)">angle of incidence</span>.

4

Measure an angle<span style="color: rgb(255, 238, 0); font-weight: bold"> equal </span>to the angle of incidence on the other side of the normal.&nbsp; This angle is called, the <span style="font-weight: bold; color: rgb(255, 238, 0)">angle of reflection</span>.&nbsp;

5

Draw a <span style="font-weight: bold; color: rgb(255, 238, 0)">reflected light </span>ray coming <span style="font-style: italic">away </span>from the mirror at this angle. Remember to put an <span style="font-weight: bold; color: rgb(255, 238, 0)">arrowhead</span> on the reflected ray.

6

Example in daily life

• Mirrors can be used to see behind us.

LB Activity (page 192)

Self-survey: Rate your level of understanding and participation in this lesson.

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