## Optics Midterm Practice

1-15True/False: Show your work where appropriate.

1-2: Refer to this picture where a ray originates in medium 1

____1. The speed of light in medium 2 is less than the speed of light in medium 1

____2. 1will be equal torefl.

____3. When light speeds up in crossing a boundary between two media at a non-zeroangle, it always bends.

____4. Light that travels between two points always takes the path with the shortest time.

____5. Light that travels between two points in the same medium without reflecting always takes the path with the shortest time.

____6. A beam of light will bend in all cases when traveling from one medium to another if each medium has a different index of refraction.

____7. A basic requirement to see an object is that light must be able to travel from the object to your eye.

____8. A pinhole imager works by allowing rays from one point on the object to reach one, and only one point on the screen.

____9. Images are located where lines of sight cross, or appear to cross.

10-12: Somehow two rays follow this bizarre path from an object at point A to your eyes.

____10. Based on the information your eyes receive, your brain will think that the object is located at point A.

____11. Your brain will use the input from your eyes to locate the image at point B.

____12. If you were to put your eyes near point C you could be sure the object was located at point A based on what you saw.

____13. Rays that leave a point on an object always take the same time to travel to the corresponding image point, even if they go through a thicker part of a lens.

____14. You can tell the difference between a real and a virtual image just by looking at it with your eye.

____15. Sometimes an image can form on the back of your retina that is virtual.

Long Answer:For mathematical problems, do the algebra first. Watch units and sig figs!

16. You are trapped in a dark room. To escape, you must reflect light from point A under a shelf, onto a photocell at point C on the ceiling using a tinymirror at point B. At what angle θ from the horizontal should you tilt the mirror? Sketch the mirror and the relevant beam of light. Measure and indicate the angle of incidence and the angle of reflection.

17. What path will the beam of light take as it passes through the water droplet surrounded by air? Sketch the beam, inside and outside the water droplet.No calcs required. Draw the normals.

18. Sketch the path the beam will take as it travels through the thick glass sheet and back out into the air.No calcs required. Draw the normals.

19. Your mom needs an operation andshedidn’t sign up for Obama Care. A friend offers you a cheap price on some “diamonds” saying that you can resell them at a profit. You test them out and find that an angle of incidence in air of θ1 = 75.0o leads to an angle of refraction of θ2 = 59.8o. Are these real diamonds? Should you buy them? Find the index of refraction of the “diamonds.”Assume you like your mom. Sketch it!

20. A particular kind of glass has an index of refraction of 1.52.

A) What is the speed of light in this material?

B) Consider a sample of this glass in water (look up the index of refraction for water in your PJ.) If θ1 = 47.5o in water, find θ2 in the glass. Sketch it!

21. There is a candle at one end of a large box and a sheet of film on the opposite wall as shown. You expose the film for a brief period of time, then you develop it. What does the developed film look like? Explain.

22. State the general requirement for an optical device to form an image.

23. Add an optical device of your choosing to form an image of the candle on the film. Assume some light

makes it to the bottom of the candle. Ray trace it!

Ray trace the following and describe the images. Color code your rays and use solid and dotted lines

appropriately. Put arrowheads on each line segment. Draw and label each image.Use your ruler!

24. Do the ray tracing for this concave mirror.

Sketch where you would have to put your eyes to see the image.

25. What would happen to the image in the case above if half of the mirror was covered up? Does it matter which half?

26. Do the ray tracing for this concave mirror.

Sketch where you would have to put your eye to see the image (without using a screen.)

27. Do the ray tracing for this converging lens.

Sketch where you would have to put your eyes to see the image.

28. Suppose the object distance so for problem 27 was 3f. Find the image distance si and the magnification M.

29. Suppose that the ray tracing above in problem 27 were to scale. Measure so, si and calculate the magnification M. Does this magnification agree with your results in problem 26?

30. You look at a beautiful rainbow from a spray with your garden hose with both of your eyes.
A) Does your right eye see the center of the rainbow arc in the same point relative to the background as your left eye? Briefly explain.

B) Where is the image of the rainbow located? Hint: how does the direction of the two rays leaving the top of the rainbow that travel to your right and left eye compare?

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