VI. OPTICS ORGY

2008 rules

A. Objective

The objective of Optics Orgy is to use various lenses and mirrors individually or in combination to produce an image of a light cross at a specified point along an optical rail.

A group of no more than three (3) team members from each school may participate in this event.

B. Equipment

The following may be available:

• 1. A two-meter optical rail with centimeter markings.
• 2. An object consisting of a lighted cross.
• 3. A white screen.
• 4. A 10 cm focal length double convex lens.
• 5. A 20 cm focal length double convex lens
• 6. A 20 cm focal length double concave lens.
• 7. A plane mirror.
• 8. A 26.3 or 29.0 cm focal length convex mirror.
• 9. A 26.3 or 29.0 cm focal length concave mirror.
• 10. A mounted vertical post (to locate images by parallax.)

C. The Competition

Teams will be asked to use certain of the above listed optical components as specified by the judges to produce either a real or a virtual image of the object at a particular point along the optical rail. You will then proceed in three steps:

• (1) Calculate where the image should be.
• (2) Position your optical components at the calculated points with the object light OFF.
• (3) Turn ON the object light.
• (4) Correct the positions of any components to obtain the required image.

Note: The position of the object will be fixed by the judges, and the object is not to be moved.

Individual setups will be presented to the competing group. The group may choose which problems they will attack, and can either work together on each problem, or divide up the problems and work individually, or any combination thereof. The total score depends only on how many setups are solved, not on which ones are solved or the order in which they are solved.

D. Individual Setup Scoring Proceedures

Each of the individual setups will be worth 10 points. If the calculation is done perfectly a score of 5 points will be earned. A minor numerical error will result in loss of one or two points, errors in sign conventions or major numerical errors (for example, using your calculator wrong) will result in loss of three or four points, and errors in the equation used will result in a score of zero.

Calculations will be done using the white boards, and must be done before the source is turned ON to be counted.

If the actual physical setup is correct with all elements within 1 cm of their true positions (as specified by the judges) three points will be awarded. If this setup is obtained before the source is turned ON, with no adjustment (C-4 above), an additional two points will be awarded, for a total of 5 experimental points.

If you are able to determine the correct position of the optical elements using ray tracing or any other means, and can set up the system within the prescribed 1 cm before turning the source ON, the maximum of 5 experimental points will be allotted. Simply turning ON the source and finding the image within 1 cm by moving the elements around will accrue a score of 3 points per setup.

E. Example

Suppose you are asked to use the 20 cm focal length double convex lens to produce virtual image of the object 10 cm behind the object.

Some of you will immediately recognize that this is a simple magnifying glass, but not know how to calculate it. So by turning on the light you can move the object around until you get the image at the right point and get 3 points. You determine the image position by putting the post at that location and using parallax. (Try it!)

Others will be able to write down a formula relating object distance, image distance, and focal length for a lens, but may forget the sign conventions for imaginary images, and therefore be unable to complete the calculations. For this effort an additional 2 or 3 points is awarded.

Some groups may write down the proper equation: 1/Ob + 1/Im = 1/f

With I = -10cm, and f = + 20 cm, and solve for 0 = 6 2/3 cm, to obtain the entire 5 points. Placing the lens 6 2/3 cm in front of the object and checking by parallax by positioning the post 10 cm behind the object, this group then accrues 5 experimental points for a total of 10 points for this setup.

F. Judging and Scoring

1. Event Score - The Event Score will be the sum of Individual Set-up Scores (max possible (5 pts/set-up) (10 setups) = 50 points).

2. Team Score - The maximum Team Score (40 points will be awarded to the team with the Highest Event Score. Other teams will receive Team Scores based on their Event Score with respect to the top team's Event Score.