Shop Windows to the Universe

We now offer the Cool It! card game in our Science Store. Cool It! is the new card game from UCS that teaches kids about the choices we have when it comes to climate change.

Charged Particle Motion in Earth's Magnetosphere

Drift Motion of Charged Particles

If a uniform electric field vector E is added the magnetic field vector B the charged particle experiences a force:

in addition to the magnetic force:

The total force on the particle is thus:

Only the electric force can do work on the particle since the magnetic force is always perpendicular to the particle velocity. If both vector v and vector E are perpendicular to vector B,

acceleration by the electric field changes the circular motion shown on the preceding page.

In the segment of its orbit when the particle is moving in the direction of the electric force, it accelerates, and its gyroradius expands. When it moving against the electric force, it decelerates and its gyroradius contracts. These distortions of the gyroradius cause the particle to drift in a direction perpendicular to both vector E and vector B.

Notice in the following animation how the velocity increases during the particle's downward swing, reaching its maximum at the base of the orbit. The veclocity vector has a rightward component during the half of the orbit when it is strongest, while it has a leftward component during the half when velocities are weakest. The net effect is a rightward drift.

Animation courtesy the COMET and HAO programs at UCAR/NCAR.

These distortions of the gyroradius cause the particle to drift in a direction perpendicular to both vector E and vector B. The average drift velocity is given by:

This kind of drift can be induced by any effect that modifies a particle’s gyroradius over the course of its orbit.

Last modified May 17, 2005 by Randy Russell.

Shop Windows to the Universe Science Store!

Learn about Earth and space science, and have fun while doing it! The games section of our online store includes a climate change card game and the Traveling Nitrogen game!

You might also be interested in:

Traveling Nitrogen Classroom Activity Kit

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

Charged Particle Motion in Earth's Magnetosphere

Motions within Earth's metallic core generate the planet's global magnetic field. This magnetic field extends beyond Earth's surface and atmosphere into the space surrounding our home planet. The interaction...more

Altocumulus

Altocumulus clouds are part of the Middle Cloud group. They are grayish-white with one part of the cloud darker than the other. Altocumulus clouds usually form in groups. Altocumulus clouds are about...more

Altostratus

Altostratus clouds belong to the Middle Cloud group. An altostratus cloud usually covers the whole sky. The cloud looks gray or blue-gray. The sun or moon may shine through an altostratus cloud, but will...more

Cirrocumulus

Cirrocumulus clouds belong to the High Cloud group. They are small rounded puffs that usually appear in long rows. Cirrocumulus are usually white, but sometimes appear gray. Cirrocumulus clouds are the...more

Cirrostratus

Cirrostratus clouds belong to the High Cloud group. They are sheetlike thin clouds that usually cover the entire sky. The sun or moon can shine through cirrostratus clouds. When looking at the sun through...more

Cirrus

Cirrus clouds are the most common of the High Cloud group. They are made of ice crystals and have long, thin, wispy streamers. Cirrus clouds are usually white and predict fair weather. ...more

Cumulonimbus

Cumulonimbus clouds belong to the Clouds with Vertical Growth group. They are also known as thunderstorm clouds. A cumulonimbus cloud can grow up to 10km high. At this height, high winds make the top...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part by the National Science Foundation and NASA, our Founding Partners (the American Geophysical Union and American Geosciences Institute) as well as through Institutional, Contributing, and Affiliate Partners, individual memberships and generous donors. Thank you for your support! NASA AGU AGI NSF