Teaching Physics with the Physics Suite
Edward F. Redish
Alice is in Looking-Glass House (having passed through the mirror in Lewis Carroll’s Alice Through the Looking Glass) and is being visited by her friend Aslan, from Narnia.
A. They are standing in front of the mirror (a few feet away) and it is of a size that Alice discovers that when she is standing next to Aslan, her image just all fits in the mirror – the top of her head appears at the top of the mirror and her feet are just visible at the bottom. But she can only see 2/3 of Aslan. (She is 4 feet tall, while he is 6.) How tall is the mirror? Draw a careful ray diagram to demonstrate your reasoning.
B. If she steps back to twice the distance, she finds that her feet still are just visible at the bottom of the mirror. Does she see the top of her head in the mirror? If so, where? Explain your reasoning.
C. If Aslan has stayed where he was when she stepped back, will she now be able to see more of him or less? Explain your reasoning with a ray diagram.
Page last modified April 11, 2012: OP46