Mirror Height Activity

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Reflection and Refraction Light Activities
Fall 2009-Day 5

In class, the students explored one of the homework questions that they had had trouble with. The question was

“How much of a mirror do we need to see all of ourselves in it?”

The guiding principle behind this activity for this group was the integration of the question with the powerful ideas about light. To begin to explore this question, the students discussed what they already knew. This included everyday knowledge about mirrors, their bodies, light, etc., as well as the powerful ideas that the students had previously generated about light.


Using what they already knew from previous explorations, the students drew a picture to illustrate the phenomena that was occurring. Each group drew a ray diagram on their white boards. There was a ray drawn from a person’s feet to the reflection off the mirror to their eyes, and from the top of their head to the reflection off the mirror to their eyes. This showed how much of the mirror was actually used.drawingmirrorheight.jpg

"To see all of ourselves in the mirror, the mirror needs to be half of our height."

Through the use of their diagrams, the answer that had been so tricky to arrive at at home, became very evident.

mirrorheightraydiagram.jpgThe answer ended up being half of a person's height. Each group had a slightly different way of explaining this phenomena in front of the class. They also found out that you still only need half of your height to see all of yourself in a mirror if you are further away from the mirror. Everyone thought this was fascinating because it is not what they had expected!

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