Question

The rod and cone cells in the central part of the retina-the fovea-are packed closer together, giving a more detailed view. This area of increased rod and cone density has a diameter of about 1.5 mm. When you read a book, you want the image of the text you are reading to fall on the fovea. If you hold a book 30 cm from your eyes, how wide is the spot on the page whose image just fills the fovea? Express your answer with the appropriate units.

Answer 1

The width of the spot on the page that fills the fovea can be calculated using similar triangles.

Since the fovea has a diameter of about 1.5 mm and the book is held 30 cm away from the eyes, we can determine the width of the spot on the page.

To find the width, we can set up a proportion using the similar triangles formed by the distance from the eyes to the page and the distance from the eyes to the fovea. The proportion would be:

(Width of spot on page) / (Distance from eyes to page) = (Diameter of fovea) / (Distance from eyes to fovea)

Substituting the given values, we have:

(Width of spot on page) / 30 cm = 1.5 mm / (Distance from eyes to fovea)

Solving for the width of the spot on the page, we can multiply both sides of the equation by 30 cm:

Width of spot on page = (1.5 mm / (Distance from eyes to fovea)) * 30 cm

The specific value for the width of the spot on the page can be calculated based on the distance from the eyes to the fovea, which would depend on the individual's eye anatomy and focusing ability.

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