Home Project Ideas Project Guide Ask An Expert Blog Careers Teachers Parents Students

Simple Circuit Logic with Switches: An Electric Puzzle *

Difficulty
Time Required Average (6-10 days)
*Note: This is an abbreviated Project Idea, without notes to start your background research, a specific list of materials, or a procedure for how to do the experiment. You can identify abbreviated Project Ideas by the asterisk at the end of the title. If you want a Project Idea with full instructions, please pick one without an asterisk.

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.

Share your story with Science Buddies!

I did this project I Did This Project! Please log in and let us know how things went.


Last edit date: 2013-01-10

Bibliography

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

Share your story with Science Buddies!

I did this project I Did This Project! Please log in and let us know how things went.

Ask an Expert

The Ask an Expert Forum is intended to be a place where students can go to find answers to science questions that they have been unable to find using other resources. If you have specific questions about your science fair project or science fair, our team of volunteer scientists can help. Our Experts won't do the work for you, but they will make suggestions, offer guidance, and help you troubleshoot.

Ask an Expert

Related Links

If you like this project, you might enjoy exploring these related careers:

Two electricians working.

Electrician

Electricians are the people who bring electricity to our homes, schools, businesses, public spaces, and streets—lighting up our world, keeping the indoor temperature comfortable, and powering TVs, computers, and all sorts of machines that make life better. Electricians install and maintain the wiring and equipment that carries electricity, and they also fix electrical machines. Read more
industrial engineer making notes in warehouse

Industrial Engineer

You’ve probably heard the expression "build a better mousetrap." Industrial engineers are the people who figure out how to do things better. They find ways that are smarter, faster, safer, and easier, so that companies become more efficient, productive, and profitable, and employees have work environments that are safer and more rewarding. You might think from their name that industrial engineers just work for big manufacturing companies, but they are employed in a wide range of industries, including the service, entertainment, shipping, and healthcare fields. For example, nobody likes to wait in a long line to get on a roller coaster ride, or to get admitted to the hospital. Industrial engineers tell companies how to shorten these processes. They try to make life and products better-finding ways to do more with less is their motto. Read more
electrical engineer aligning laser

Electrical & Electronics Engineer

Just as a potter forms clay, or a steel worker molds molten steel, electrical and electronics engineers gather and shape electricity and use it to make products that transmit power or transmit information. Electrical and electronics engineers may specialize in one of the millions of products that make or use electricity, like cell phones, electric motors, microwaves, medical instruments, airline navigation system, or handheld games. Read more