Science Buddies: "Ask an Expert"

In the project https://www.sciencebuddies.org/science- ... p028.shtml

How Do I determine the Distance Ratio?

Please post your query again. The link you provided was not valid and I do not understand your project or problem.

Link Fixed. Also I realized that I have to devide masked by unmasked Kohms, but what do they mean by unmasked?just take off the blades and use the cds photosensor freely without them?

Looks like we had crossing e-mails.

You are correct in how to calculate Distance Ratio.

Here is how I understand the experiment. For your first trial, you make the slit. You use the method mentioned in Step 6 to calculate its width. This cardboard with the razor blade slit on it is your MASK. You put the MASK right in front of the photocell and take a resistance measurement. You measure the distance from the razor blade slit to the light source. This is your SHORT distance. Then you take the MASK away from the photocell. Then you move the whole thing farther from the light source until your photocell gives you the same resistance measurement. This is your LONG distance. Divide the SHORT distance by the LONG distance. This is your DISTANCE RATIO.

For you next trial, you move the razor blades apart a bit, creating a new MASK, recalculate the slit width, and run the same experiment again, with and without the mask. Fill out a table like the one shown, making multiple trials by moving the razor blades farther apart.

Good luck.

Thanks so much, last question.. on the voltmeter do I select 2M, 200k, 20k, 2k, or 200?

Start with the highest resistance scale (2M in your case) and see what reading you get. In order to get more significance, you then switch to a lower resistance scale that is the one just greater than your initial reading. For example, if you see something in the 150K ohm range on the 2M ohm scale, switch to the 200K ohm scale. If you get something in the 5K ohm range, use the 20K ohm scale. In other words, pick the scale that is above the actual reading such that the next lower ohm scale would be below the reading.