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Simple Circuit Logic with Switches: An Electric Puzzle

Summary

Areas of Science
Difficulty
 
Time Required
Average (6-10 days)
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Abstract

Here's a puzzle you may have heard before which you can build as a simple electric circuit. First, the puzzle: a farmer is traveling to market with his cat, a chicken and some corn. He has to cross a river, and the only way to cross is in a small boat which can hold the farmer and just one of the three items he has with him. The problem is, he has to be very careful about what he chooses to leave behind at any time. If the cat and chicken are left alone, the cat will eat the chicken. If the chicken and the corn are left alone, the chicken will eat the corn. To solve the puzzle, you must show how the farmer can get himself and his three items across the river without losing any of them. The goal of this project is to design a simple electrical circuit that follows the puzzle. You'll need a 6 V battery, a flashlight bulb, a bulb holder, some connecting wire, and four toggle switches: 3 SPDT (single-pole, double throw) and 1 DPDT (double-pole, double throw). Each switch represents one of the items: the farmer, the cat, the chicken and the corn (you have to figure out which need to be SPDT switches and which one needs to be a DPDT switch). The switches are mounted on a small panel, in a horizontal row (representing the river, which you can draw in). Each switch is labeled ("Farmer", "Cat", "Chicken", "Corn"). The circuit is to be designed so that if either of the problematic pairs (cat-chicken, or chicken-corn) are left alone on the same side of the river, the light bulb lights up, indicating an incorrect solution (you can add a 6 V buzzer, too, if you like). Since the boat can hold only two items, players can use only two switches per "move". Irwin Math's book, Wires and Watts: Understanding and Using Electricity has the solution (Math, 1981, 67-70), but see if you can figure this one out on your own.

Bibliography

Math, I., 1981. Wires and Watts: Understanding and Using Electricity. New York, NY: Charles Scribner's Sons.
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MLA Style

Science Buddies Staff. "Simple Circuit Logic with Switches: An Electric Puzzle." Science Buddies, 20 Nov. 2020, https://www.sciencebuddies.org/science-fair-projects/project-ideas/Elec_p046/electricity-electronics/simple-circuit-logic. Accessed 17 May 2022.

APA Style

Science Buddies Staff. (2020, November 20). Simple Circuit Logic with Switches: An Electric Puzzle. Retrieved from https://www.sciencebuddies.org/science-fair-projects/project-ideas/Elec_p046/electricity-electronics/simple-circuit-logic


Last edit date: 2020-11-20
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