Magnetohydrodynamics and the Lorentz Force Law

A Presentation for Grade 12 Physics Students

By Reg Milley and Physics 420, U.B.C


Magnetohydrodynamics is a subject that concerns itself with several branches of fundamental physics, in particular electricity and magnetism, and thus makes a good demonstration for the senior high school years. Magnetohydrodynamics, or MHD for short, is an application of the Lorentz Force Law which can be used to propel boats and such in an ionic solution, such as salty sea water.

This type of propulsion unit is still being considered as an efficient mode of transportation by some industries of the world however there are still some major engineering problems to overcome. For example the average magnetic field strength to propel a freighter would have to be in the order of 8 to 20 teslas (a fridge magnet, that you would find in your home, is only about 0.01 tesla!). A way to overcoming this particular problem is through the use of high temperature superconducting magnets.

This presentation will be primarily concerned with the theory behind the operation of a magnetohydrodynamic propulsion mechanism that will propel a model boat in a pool of salt water. The static display and the converted model boat are a relatively inexpensive way to demonstrate some fundamental theories of electricity and magnetism. The total cost should not exceed the 200 dollar mark (depending on the resources available to you). The presentation itself might have some added demonstrations involving the relationship between electricity and magnetism (for example to make an electromagnet out of a nail and some copper wire.), but in general the core presentation is to explain, at a senior high school level, the concept of magnetohydrodynamics.

Main Menu

The Lorentz Force Law and the Right Hand Rule

General MHD Setup and Direction Calculation

The Magnitude of the Force

The Boat and Static Display

The Curious MHD Circuit (Do electrons "flow" through water?)

There exists at least one other design for a MHD powered boat of this nature which might be a good reference for any students interested in building one for themselves: