Challenge: To design an electromagnetic field manipulator that can change the direction of the earth’s magnetic field up to 100° in either direction using as little electrical power as possible.
Parameters: You must design and build adjustable electromagnet(s) that will change the direction of a compass by up to 100° in either direction. Your electromagnet(s) must be built around an imaginary box at least 10 cm wide and 5 cm tall, and unobstructed on one side, so you can insert a compass or a phone to measure the magnetic field vectors with the Phyphox app. To measure electrical efficiency, your device should have an easy way to connect an ammeter and voltmeter, and must demonstrate its ability to cancel the horizontal component of the Earth’s magnetic field (to below 1µT). Your device must not use any permanent magnets or any magnetic shielding materials. Your device must use salvaged magnet wire from electronic waste, not purchased materials. You must know the physical parameters of your device in detail. (Number of wraps, gauge of wire, etc.)
Scoring: Your system will be scored on the basis of the electrical efficiency of the electromagnet, and the accuracy of the compass deflections asked of you during the contest. You will be given three deflections and will have to adjust your device to achieve those deflections before the compass is inserted.
Score = Power use (Watts) + Average Angle Difference (°)
Rank will be based on score, with lowest scores ranked highest
Physics: Moving charges will result in a magnetic field. Multiple loops of current-carrying wires will have a large magnetic field in the enclosed space. The field depends on the current and on the number of wraps you can do per cm of length.
Extensions: Research the design of electromagnets and air-core solenoids. Especially Helmholtz coils! Also; wire gauge and current capacity, and how magnetic field sensors work.
Help/Hints: You can obtain wire by dismantling salvaged transformers or motors, but be careful not to damage the insulation, which is often a thin layer of enamel. The gauge of the wire is important as thinner wires can be wrapped more times, but have more resistance and waste more energy as heat. Find out the location of the magnetic field sensors in your phone, and compare the phone results with the behaviour of an actual compass needle.
Quiz Topics: Electromagnetism (Induction and Forces), Simple Circuits.
Online Text: Ch 22, Ch 23