# Physics

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True/False

1)The lens of the eye has a fixed focal length.

False.

2)What must be the minimum height of a plane mirror so that a boy of height 162 cm can view himself from head to toe?

162 cm. The image formed in a plane mirror is the same size as the object and is the same distance behind the mirror as the object is in front.

• Physics -

1) is correct, but as one gets older, the eye's ability to change focal length is lost.

2) is wrong. Draw yourself a ray diagram with a shorter mirror. The ray that comes from your feet hits the mirror about half way up before reaching your eye. Mirror area below waist level never gets used forming the virtualimage of yourself. Draw rays from your eye to the top and bottom of the image of yourself. How much of the mirror is used?

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