April 15, 2013
Magnets, with their magical action-at-a-distance property, have inspired many a child's interest in science. Permanent magnets, and a variety of electromagnets I built when I was about nine years old, were the probable catalyst for my physics career.
Many movies of the era portrayed laboratories with bubbling flasks of chemicals, and I played with chemistry sets for a time. Electricity, however, was a more fascinating subject, especially when sparks were involved.
One method for generating sparks is to connect an inductor to a hefty battery and momentarily touch the wire ends to complete and break the circuit (see figure). If you want to create a lot of sparks, as I did as a child, you would connect one wire to a metal file and scrape the other wire across the file.
To paraphrase the expression about mirrors, it's all done with magnetism. It also generates radio frequency interference, so don't use too large a battery. Of course, the usual disclaimers about parental supervision, safety glasses, etc., apply; and, there's also an electrical shock hazard.
Our knowledge of magnetism goes back at least to the sixth century B.C. to the Greek philosopher, Thales. Thales wrote about the attraction of lodestones, which are magnetized specimens of the mineral, magnetite (Fe3O4), to themselves, and to iron. The Earth's magnetic field was made apparent with the first magnetic device, the compass, also known from antiquity.
The first modern study of magnetism was done by the English scientist, William Gilbert, and published in 1600 as De Magnete. Gilbert provided evidence that the Earth was a giant magnet, and he actually created a sphere of lodestone, which he called a terrella, as a model to prove his theory.
Gilbert's De Magnete was not just concerned with the magnetic moment of the Earth. It included information on practical magnetism, such as the method shown in the following woodcut for magnetizing a piece of iron.
|Creating sparks with an inductor. The stored energy in a magnetic field is discharged as a spark when the electrical circuit is broken. (Illustration by the author using Inkscape.)|
The intensity of Earth's magnetic field, 0.25 to 0.65 gauss when measured at its surface, is small compared with that of permanent magnets. The barium ferrite (BaFe12O19) component of composite refrigerator magnets has a field strength of up to several thousand gauss. Small though it may be, we're fortunate that Earth has a magnetic field, since it directs cosmic rays around the Earth.
Cosmic rays are charged particles, so they experience a force when moving in a magnetic field, much like a current-carrying wire will be deflected when a magnet is brought nearby. An interesting example of this effect is the dancing filament of an incandescent light bulb incorporating a permanent magnet. The Earth's magnetic field lines deflect most cosmic rays to the poles, where they are manifest in auroral displays.
Mars, however, doesn't have a global magnetic field. That, and its lack of a dense atmosphere, will make conditions difficult for astronauts. Its lack of a global magnetic field may be the reason why Mars has so little atmosphere, since the solar wind would have stripped it away over the course of billions of years.
NASA has planned a space probe, the Mars Atmosphere and Volatile Evolution (MAVEN) mission, scheduled for launch this year. One purpose of this probe is to do a careful magnetic survey of Mars, which still retains patches of magnetic field in its crust (see figure). MAVEN will reach Mars orbit in September 2014.
Small though they be, these magnetic patches might create pockets of atmosphere that are protected from the solar wind and cosmic rays. The magnetometers of MAVEN are sensitive flux-gate devices based on the magnetic saturation of a material. When exposed to a magnetic field, such materials will saturate magnetically more quickly in one direction than the other. The electronics to sense such a change is easy to design, but the power demand of the saturating coils is often a problem.
The biggest problem NASA faces is creating a "magnetically clean" spacecraft; namely, one in which its materials of construction and electrical currents for operation won't generate false signals. When probing Mars for very small magnetic fields, every stray bit of magnetic field in the spacecraft would generate measurement errors.
|Magnetizing an iron piece.|
Hot iron is worked on an anvil with its axis aligned north-south.
The Latin word for North is septentrio, and the Latin word for south is avster/auster).
(Via Wikimedia Commons.)
- Please read our Site Disclaimer. "The scientific procedures and experiments described on these pages assume an appropriate level of adult supervision, safety training, personal protective equipment (such as safety glasses, etc.), and other safety facilities. You must follow all the customary, prudent, and necessary procedures of the appropriate scientific discipline for the following: 1) Safe storage, preparation, handling, and disposal of any chemicals or other potentially dangerous materials mentioned in these pages. 2) Safe use of machines, experimental apparatus, and other equipment."
- William Gilbert, "De Magnete," 1600 (original Latin); English translation. The illustration is from Book III, Chapter XII.
- Robert J. Kyp, "Electric Light Bulb with Oscillating Filament," US Patent No. 3,237,053, February 22, 1966.
- Claire De Saravia, "Measuring Mars: The MAVEN Magnetometer, NASA Goddard Space Flight Center Press Release, March 26, 2013.
- Magnetic putty absorbing a rare-earth magnet, YouTube video, Mar 25, 2013.
Permanent Link to this article
Linked Keywords: Magnet; action-at-a-distance; child; science; permanent magnet; electromagnet; catalyst; physics; film; movie; laboratory; bubble; bubbling; Erlenmeyer flask; flask; chemical substance; chemical; chemistry set; electricity; electric spark; inductor; battery; wire; circuit; metal file; paraphrase; mirror; magnetism; electromagnetic interference; radio frequency interference; disclaimer; parental supervision; safety glasses; electric shock; electrical shock hazard; magnetic field; Inkscape; sixth century B.C.; Greek philosopher; Thales; lodestone; magnetite; iron; Earth's magnetic field; compass; English people; scientist; William Gilbert; De Magnete; Earth; terrella; physical model; magnetomotive force; scientists whose names are used as non SI units; International System of Units; SI unit; cgs unit; Charles Henry Granger (1812-1893); Wikimedia Commons; woodcut; anvil; north; south; Latin; Earth's magnetic field; gauss; barium ferrite; refrigerator magnet; cosmic ray; electric charge; particle; Fleming's left-hand rule; electric current; current-carrying; incandescent light bulb; US Patent No. 3,237,053; pole; auroral displays; Mars; atmosphere of Mars; astronaut; solar wind; NASA; space probe; Mars Atmosphere and Volatile Evolution; MAVEN; crust; mineral; magnetometer; flux-gate; magnetic saturation; electronics; electric power; solenoid; coil; observational error; measurement error; Site Disclaimer.
Latest Books by Dev Gualtieri
Thanks to Cory Doctorow of BoingBoing for his favorable review of Secret Codes!
Blog Article Directory on a Single Page
- Soybean Graphene - March 23, 2017
- Income Inequality and Geometrical Frustration - March 20, 2017
- Wireless Power - March 16, 2017
- Trilobite Sex - March 13, 2017
- Freezing, Outside-In - March 9, 2017
- Ammonia Synthesis - March 6, 2017
- High Altitude Radiation - March 2, 2017
- C.N. Yang - February 27, 2017
- VOC Detection with Nanocrystals - February 23, 2017
- Molecular Fountains - February 20, 2017
- Jet Lag - February 16, 2017
- Highly Flexible Conductors - February 13, 2017
- Graphene Friction - February 9, 2017
- Dynamic Range - February 6, 2017
- Robert Boyle's To-Do List for Science - February 2, 2017
- Nanowire Ink - January 30, 2017
- Random Triangles - January 26, 2017
- Torricelli's law - January 23, 2017
- Magnetic Memory - January 19, 2017
- Graphene Putty - January 16, 2017
- Seahorse Genome - January 12, 2017
- Infinite c - January 9, 2017
- 150 Years of Transatlantic Telegraphy - January 5, 2017
- Cold Work on the Nanoscale - January 2, 2017
- Holidays 2016 - December 22, 2016
- Ballistics - December 19, 2016
- Salted Frogs - December 15, 2016
- Negative Thermal Expansion - December 12, 2016
- Verbal Cues and Stereotypes - December 8, 2016
- Capacitance Sensing - December 5, 2016
- Gallium Nitride Tribology - December 1, 2016
- Lunar Origin - November 27, 2016
- Pumpkin Propagation - November 24, 2016
- Math Anxiety - November 21, 2016
- Borophene - November 17, 2016
- Forced Innovation - November 14, 2016
- Combating Glare - November 10, 2016
- Solar Tilt and Planet Nine - November 7, 2016
- The Proton Size Problem - November 3, 2016
- Coffee Acoustics and Espresso Foam - October 31, 2016
- SnIP - An Inorganic Double Helix - October 27, 2016
- Seymour Papert (1928-2016) - October 24, 2016
- Mapping the Milky Way - October 20, 2016
- Electromagnetic Shielding - October 17, 2016
- The Lunacy of the Cows - October 13, 2016
- Random Coprimes and Pi - October 10, 2016
- James Cronin (1931-2016) - October 6, 2016
- The Ubiquitous Helix - October 3, 2016
- The Five-Second Rule - September 29, 2016
- Resistor Networks - September 26, 2016
- Brown Dwarfs - September 22, 2016
- Intrusion Rheology - September 19, 2016
- Falsifiability - September 15, 2016
- Fifth Force - September 12, 2016
- Renal Crystal Growth - September 8, 2016
- The Normality of Pi - September 5, 2016
- Metering Electrical Power - September 1, 2016
Deep Archive 2006-2008