An Exploration of the Physics Behind Rail Guns
Daniel Lenord
University of Alaska Fairbanks
Physics 212 Web Project, Spring 2003

   A rail gun in it's simplest form is a pair of conducting rails separated by a distance L and with one rail connected to the positive and one the negative side of a power source supplying voltage V and current I. A conducting projectile bridges the gap L between the rails, completing the electrical circuit. As current I flows through the rails, a magnetic field B is generated with an orientation dictated by the right hand rule and with a magnitude governed by the following equation.

B=NuI

• B=Magnetic field strength (Teslas)
• N=Number of turns in solenoid (1 in our case)
• u=1.26x10^-6 (The magnetic permeability of free space, Henries/Meter)
• I=Current through rails and projectile (Amperes)

Simple Rail Gun

When a current I moves through a conductor of length L in the presence of a magnetic field B, the conductor experiences a force F according to the following.

F=ILB

• F=Force on conductor (projectile, in Newtons)

• I=Current through rails and projectile (Amperes)

• L=Length of rail separation (Meters)

• B=Magnetic field strength (Teslas)

The direction of the force depends on the direction of the current through the projectile and the magnetic field since the force is truly a vector with direction dictated by the cross product of the vector quantities I and B.