Lifting Electromagnet

Challenge:  To design a lifting electromagnet that is as efficient as possible

Parameters: You must design and build an electromagnet that will lift a 10 cm by 20 cm by 2.5 cm, 4.0 kg block of steel 5.0 cm off the table for a minimum of 30 seconds, as efficiently a possible.  The interface between your magnet and the steel block must be flat and horizontal, and cannot involve any kind of adhesion.  Your electromagnet must fit within a 5.0 cm radius cylinder 10 cm tall.  You will be using a variable power supply to control the power applied to the electromagnet.  An ammeter and voltmeter will be included in your circuit to calculate the electromagnet’s power consumption.  You cannot use any purchased materials, or any components that were originally electromagnets.  There can not be any permanent magnets in your device, and it must drop the steel block within one second of being powered off.

Scoring:  Your system will be scored on the basis of the efficiency of the electromagnet. The mass of the steel block is a constant, so you want to minimize the power consumption of your electromagnet.  If your electromagnet cannot lift the block, you will be scored on the amount of flux it produces per Ampere of current used by the solenoid(s)

Score = (4.0 kg) / (I • V) or flux (in µWb) per Ampere

Rank will be based on score, with all successful lifters scored above those who don't.

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, which will be even larger if the space is occupied by iron or other ferromagnetic material.  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 contrast them with the design of transformers.  Why must transformers have different core designs?  Research the electromagnets used in the ITER fusion experiment.  How do they get such huge magnetic fields?  Research DC motors that have permanent magnets compared to AC motors.  Are there advantages to both designs?

Help/Hints: The field is strongest at the surface of the metal core, so make sure it is as flat as possible.  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.

Quiz Topics: Electromagnetism (Induction and Forces), Simple Circuits.

Online Text: Ch 22, Ch 23