Magnetic Torque

Claimed by Demetria Hubbard--Dhubbard8 (talk) 15:02, 2 December 2015 (EST) edited by Hannah Jang Spring 2016

Magnetic torque is a phenomenon that occurs when the magnetic field produced causes a current-carrying wire to twist out of proportion.

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Example of Magnetic Torque

The Main Idea

The idea behind this concept is that as current flows through a wire, a magnetic field is produced. While this magnetic field is being produced, there is a force acting upon the wire causing it to twist. An example of this phenomenon is the movement of a compass needle by the Earth's magnetic field. Another example is a hanging coil that twists in the direction of the magnetic field of a bar magnet.

The magnetic torque acts on the dipole, and it is highly dependent on the magnetic moment and external magnetic field.

Several factors besides the magnetic moment and external magnetic field can affect the magnetic torque. In a loop or other three dimensional object the orientation of the object relative to the magnetic field highly affects the torque.

This relationship can be seen in this video: [1]

Here is a video on Asymmetric Magnet Torque Asymmetric Magnet Torque

A Mathematical Model

This is the overall equation for determining magnetic torque.

Represents torque (in units of N*m)

is the dipole moment of the magnet (A*m^^2)

is the magnetic field created by the magnet (in units of Tesla)

A Computational Model

Click here to view the PHET Interactive Model created by the University of Colorado

PHET Interactive Magnet and Compass Model

Examples

Torque on Current Carrying Loop

Simple

A bar magnet whose magnetic dipole moment is <3, 0, 1.8> A · m2 is suspended from a thread in a region where external coils apply a magnetic field of <0.6, 0, 0> T. What is the vector torque that acts on the bar magnet?

Middling

A bar magnet whose magnetic dipole moment is 14 A · m2 is aligned with an applied magnetic field of 5.4 T. How much work must you do to rotate the bar magnet 180° to point in the direction opposite to the magnetic field?

Difficult

A cylindrical bar magnet whose mass is 0.09 kg, diameter is 1 cm, length is 3 cm, and whose magnetic dipole moment is <4, 0, 0> A · m2 is suspended on a low-friction pivot in a region where external coils apply a magnetic field of <2.0, 0, 0> T. You rotate the bar magnet slightly in the horizontal plane and release it. (For small angles in radians, assume sin(θ) ≈ θ.)

(a) What is the angular frequency of the oscillating magnet?

(b) What would be the angular frequency if the applied magnetic field were <4.0, 0, 0> T?

Connectedness

A standard compass http://helenotway.edublogs.org/2011/01/02/different-compass-point-same-ultimate-direction/

Utilizing a compass is a basic survival need and it just so happens to depend on the torque produced by the Earth's magnetic field. As a Biology major, field work is a large part of what I do, especially studying ecological systems and different habitats. In order to navigate in unfamiliar locations, such as deserts and dense tropical forests, scientists rely heavily on basic survival skills and this includes the use of compasses and maps. Physics, biology, and chemistry make up part of the science family and each heavily depends on the other, this is why it is important to study each one to bridge the relationship.

First paragraph of "Connectedness" written by Demetria Hubbard 2015

The Earth has a complex magnetic field and magnetic dipole moment that creates a magnetic torque. The necessity of all three of these magnetic properties is rarely known; however, all three are essential for life on earth. Earth's magnetic field serves to deflect most of the solar wind, so without the magnetic properties of the earth, the charged solar wind would have stripped the ozone layer from earth which would have exposed everything on earth to dangerous UV radiation.

History

Refer to Magnetic Force

See also

• Torque
• Magnetic Field
• Magnetic Force
• Bar Magnet

Further reading

• Chabay, Ruth W., and Bruce A. Sherwood. Matter & Interactions. 3rd ed. Hoboken, NJ: Wiley, 2011. Print.
• Eisberg, R. and Resnick, R. Quantum Physics of Atoms, Molecules, Solids, Nuclei, and Particles, 2nd ed. New York: Wiley, p. 269, 1985.
• Griffiths, D. J. Introduction to Electrodynamics, 3rd ed. Englewood Cliffs, NJ: Prentice Hall, p. 220, 1989.

External links

Magnetic Torque

References

• Torque Example
• Chabay, Ruth W., and Bruce A. Sherwood. Matter & Interactions. 3rd ed. Hoboken, NJ: Wiley, 2011. Print.
• "Magnet and Compass PHET Interaction Model." PhET. Ed. Chris Malley. University of Colorado, 2015. Web. 5 Dec. 2015. <https://phet.colorado.edu/en/simulation/legacy/magnet-and-compass>.
• Torque on Current-Carrying Loop in Magnetic Field. Doc Schuster. 23 Jan. 2013. Video. https://www.youtube.com/watch?v=xER1_SYql44
• http://helenotway.edublogs.org/2011/01/02/different-compass-point-same-ultimate-direction/
• Weisstein, Eric. "Magnetic Torque." Eric Weisstein's World of Physics. Wolfram Research, 1996. Web. 5 Dec. 2015. <http://scienceworld.wolfram.com/physics/MagneticTorque.html>.
• "Magnetic Torques and Amp's Law." Rochester Institute of Technology. Web. 5 Dec. 2015. <http://spiff.rit.edu/classes/phys213/lectures/amp/amp_long.html>.
• "Homework 11." WebAssign. Web. 5 Dec. 2015. <http://webassign.net/>.