|Team___________ Name_________________________ Hour____|
|Skinny lens code _______|
|Fat lens code _______|
1. Find the focal length of each lens.
Arrange the light bulb (object), the lens (one at a time), and a white 3×5 card as shown, on an "optical track." (An optical track can be nothing fancier than a meter stick on two pairs of legs, and clips for the items, like lenses, to ride on the track.)Adjust the distances until you are able to focus the image of the light bulb on the card.
With the image of the light bulb (object) focused on the card, measure (for each lens) the object-to-lens distance do, and the lens-to-image distance di.
With these data, calculate the focal length of each lens.
Equation that you used:||f skinny lens|
the focal length
|f fat lens|
the focal length
2. Combination Lens
Put the fat and skinny lenses together and use the same method as in (1) to find the focal length of the combination. (If one lens does not have a lens mount, have someone hold it next to the other lens.)
|Combination lens||do=_______cm||di=_______cm||The focal length is _______cm|
Use the theoretical equation for the focal length of two lenses together to calculate what you would expect the focal length of the combination to be, based on their separate focal lengths as determined in (1).
|Combination lens||Theoretical focal length is _______cm|
|Are you satisfied that the experimental and theoretical values agree within experimental error? If not, explain, and discuss what effort you have made to correct the situation.|
You have already met Ferdinand. Use Ferdinand as the object that your telescope will be designed to view, magnified, of course. On a piece of tracing paper (translucent paper that allows you to draw on) 6cm by 6cm, make a black ink silhouette drawing of Ferdinand. Make him exactly 5 cm tall. This will be ho. Now wrap the width of the paper in the shape of a cylindrical tube, so that you can slide the "Ferdinand" over the light bulb.
Place the 'Ferdinand' over the bulb. Place the skinny lens 60cm to the right of Ferdinand.
|Theoretical image distance, di is _______cm|
|Theoretical image height, hi is _______cm|
|Experimental image height, hi is _______cm|
4. Seeing an image in mid-air.
|When you see the image of Ferdinand without the white card, put a check mark here|
|Estimate how much larger the image is now than before|
|Theoretical magnification is _______|
Do you notice how horribly fuzzed out the colors are in the light part of the image? What is this due to?
Back to Job #1: Sally and Kenny go Wading
Back to Job #2: The famous fishing pole paradox
Back to Job #3: How a prism separates blue light from red light
Back to Job #4: The World's First Camera, or, How the Human Eye Works
Back to Job #5: The Telescope, or How the Dutch Lens Grinders Made Galileo Famous
Answers to "Job" problems
Back to Optics Main menu
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