Write small: long entry!

Seed Question: Look at some small text from a distance of a few inches so that the text is blurry. Now look through a tiny finger pinhole. Why do you see more clearly through the tiny pinhole?

Exploration: Pinhole Image Formation:

Let’s figure out the essentials of how a pinhole device makes an image of something. Imagine a candle is placed on a tiny shelf in a pinhole imaging box that is lightproof. The screen is on the back wall. Do a small sketch, less than ¼ of the page tall. Subtly shade the background in pencil.

Consider a point on the top of the candle flame. Where does light from the top of the candle flame point go? Answer in words…

Sketch at least 5 rays from the top point in yellow.

Draw the special ray in red that leaves the top of the candle and hits the screen.

Now consider light from a point on the bottom of the candle.(Assume there is some light there from the flame.)Where does light from the candle’s bottom hit the screen? Answer in words…

Sketch the ray in red.

Draw a bunch of other rays in red that leave different points on the object and hit the screen.

Draw the image of the candle on the screen. How many points on the screen can each point on the candle go to?

What is the function of the pinhole? What did it do to the rays?

Let’s look more closely. Carefully sketch the following set-up, taking care to make the object distance so twice the image distance si. Align the bottom of the candle with the pinhole and make the candle height ho= 5.0 cm. This sketch should take up half of the left hand page.

Sketch the rays (in red) from the top and bottom of the candle that hit the screen.

Draw the image. Label the image height hi.

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Top of the right hand page.

Orientation: / Erect or Inverted
Size: / Enlarged, Same or Reduced

How can you describe an image?

Highlight 2 similar right triangles, formed in part by the 2 rays.

If the magnification M = hi/ho, what is the magnification in term of si and so? (Hint: use a similar triangle argument, algebra only!)

What is the magnification in this case? (Get a number.)

Save the bottom half of the right hand page for the Big Idea.

Big Idea:

Discussion: ?