The physical principle behind an MHD propulsion system is not very complicated: An electrically charged particle moving through a magnetic field feels a force. The force is

The Physics Teacher, Vol. 42, No. 7, pp. 410–415, October 2004
©2004 American Association of Physics Teachers. All rights reserved.

The physical principle behind an MHD propulsion system is not very complicated: An electrically charged particle moving through a magnetic field feels a force. The force is

The Physics Teacher, Vol. 42, No. 7, pp. 410–415, October 2004
©2004 American Association of Physics Teachers. All rights reserved.

The physical principle behind an MHD propulsion system is not very complicated: An electrically charged particle moving through a magnetic field feels a force. The force is

where q and v are the particle charge and velocity, respectively, and B is the applied magnetic field. The resulting force is perpendicular to both the velocity of the particle and the magnetic field. Its direction may be determined with the right-hand rule, as shown in Fig. 1 (for a positive charge).

Figure 1.

In order to harness this force for propulsion, one simply passes a stream of charges through a magnetic field and the charges are accelerated. By Newton's third law, the propulsive force is exactly equal to the force imparted on the charges. Since more than one charge will be accelerated, the equation above may be recast by rewriting the term qv using

The Physics Teacher, Vol. 42, No. 7, pp. 410–415, October 2004
©2004 American Association of Physics Teachers. All rights reserved.

The physical principle behind an MHD propulsion system is not very complicated: An electrically charged particle moving through a magnetic field feels a force. The force is

where q and v are the particle charge and velocity, respectively, and B is the applied magnetic field. The resulting force is perpendicular to both the velocity of the particle and the magnetic field. Its direction may be determined with the right-hand rule, as shown in Fig. 1 (for a positive charge).

Figure 1.

In order to harness this force for propulsion, one simply passes a stream of charges through a magnetic field and the charges are accelerated. By Newton's third law, the propulsive force is exactly equal to the force imparted on the charges. Since more than one charge will be accelerated, the equation above may be recast by rewriting the term qv using

The Physics Teacher, Vol. 42, No. 7, pp. 410–415, October 2004
©2004 American Association of Physics Teachers. All rights reserved.

The physical principle behind an MHD propulsion system is not very complicated: An electrically charged particle moving through a magnetic field feels a force. The force is

where q and v are the particle charge and velocity, respectively, and B is the applied magnetic field. The resulting force is perpendicular to both the velocity of the particle and the magnetic field. Its direction may be determined with the right-hand rule, as shown in Fig. 1 (for a positive charge).

Figure 1.

In order to harness this force for propulsion, one simply passes a stream of charges through a magnetic field and the charges are accelerated. By Newton's third law, the propulsive force is exactly equal to the force imparted on the charges. Since more than one charge will be accelerated, the equation above may be recast by rewriting the term qv using

where n is the number of charges per volume, A and L are the cross-sectional area and length, respectively, of the region where the charges will travel. The quantity qnAv is then defined as the current I. This leads to the statement for the force imparted on a current in the presence of a magnetic field,

The Physics Teacher, Vol. 42, No. 7, pp. 410–415, October 2004
©2004 American Association of Physics Teachers. All rights reserved.

The physical principle behind an MHD propulsion system is not very complicated: An electrically charged particle moving through a magnetic field feels a force. The force is

where q and v are the particle charge and velocity, respectively, and B is the applied magnetic field. The resulting force is perpendicular to both the velocity of the particle and the magnetic field. Its direction may be determined with the right-hand rule, as shown in Fig. 1 (for a positive charge).

Figure 1.

In order to harness this force for propulsion, one simply passes a stream of charges through a magnetic field and the charges are accelerated. By Newton's third law, the propulsive force is exactly equal to the force imparted on the charges. Since more than one charge will be accelerated, the equation above may be recast by rewriting the term qv using

where n is the number of charges per volume, A and L are the cross-sectional area and length, respectively, of the region where the charges will travel. The quantity qnAv is then defined as the current I. This leads to the statement for the force imparted on a current in the presence of a magnetic field,

The Physics Teacher, Vol. 42, No. 7, pp. 410–415, October 2004
©2004 American Association of Physics Teachers. All rights reserved.

The physical principle behind an MHD propulsion system is not very complicated: An electrically charged particle moving through a magnetic field feels a force. The force is

where q and v are the particle charge and velocity, respectively, and B is the applied magnetic field. The resulting force is perpendicular to both the velocity of the particle and the magnetic field. Its direction may be determined with the right-hand rule, as shown in Fig. 1 (for a positive charge).

Figure 1.

In order to harness this force for propulsion, one simply passes a stream of charges through a magnetic field and the charges are accelerated. By Newton's third law, the propulsive force is exactly equal to the force imparted on the charges. Since more than one charge will be accelerated, the equation above may be recast by rewriting the term qv using

where n is the number of charges per volume, A and L are the cross-sectional area and length, respectively, of the region where the charges will travel. The quantity qnAv is then defined as the current I. This leads to the statement for the force imparted on a current in the presence of a magnetic field,

In MHD propulsion systems, the current is usually passed through a medium, such as salt water, and electro-magnets are used to apply a magnetic field perpendicular to the current path. The sodium and chlorine ions in the water act as the charge carriers. They are accelerated by the magnetic force and transfer their momentum through collisions to the water molecules. The result is that the water itself is accelerated, although the water molecules are not directly affected by the magnetic force.