This version (2016/04/28 00:54) was approved by svrijn.The Previously approved version (2012/04/18 02:50) is available.Diff

Magnet in copper tube

Introduction

A magnet dropped through a electrical conducting (copper) tube will fall slow, at constant speed.

Description of the Experiment

Drop a power full neodymium magnet through a vertical copper tube.

When the magnet falls in the gravitation field, through the tube, the acceleration is gone, so that the magnet falls with constant speed. This can bee confirmed by making the experiment with tubes of different length, and observe that the fall time is almost proportional to the length of the tube.

When the magnet falls through the tube, it will induce a current in the copper (you can think of the tube as a coil with only one turn). This current creates a magnetic field, which according to Lenz's law is directed opposite of the falling magnets field, which then is slowed down.

Be ware that you need a very powerfull magnet and a well fitting tube. This effect will dramatically drop if the experiment is carried out with a tube which has bin cut in a line in the length of the tube.

Safety Information

Very strong magnets can damage electrical equipment, like cellphones, cameras, and credit cards. Also they can hurt a small piece of skin, from the attraction to other magnets or magnetic materials, ex iron.

Equipment and materials

Power full magnet

Copper tube

References

grøn pilC.S. MacLatchy, P. Backman and L. Bogan: “A quantitative magnetic braking experiment”, Am. J. Phys. 61, 1096 (1993). grøn pilO.R. Ochoa, F. Kolp and J.T. Handler: “Quantitative demonstration of Lenz's law”, The Physics Teacher 36, 50 (1998). (http://scitation.aip.org/tpt/) grøn pilC.A. Sawicki: “A Lenz's law experiment revisited”, The Physics Teacher 38, 439 (2000). (http://scitation.aip.org/tpt/) grøn pilS. Devons: “The search for electromagnetic induction”, The Physics Teacher 16, 625 (1978). (http://scitation.aip.org/tpt) grøn pilR.C. Nicklin, A. Graham, and R. Miller: “Lenz's law demonstration for a large class”, The Physics Teacher 35, 46 (1997). (Hvordan man kan bruge kameraer til at vise forsøget for et stort publikum.) (http://scitation.aip.org/tpt) grøn pilC.A. Sawicki: “A dynamic demonstration of Lenz's law”, The Physics Teacher 35, 47 (1997). (Hvordan man kan vise forsøget til et stort publikum ved at lave et rør, der skiftevis består af kobber og gennemsigtigt plastik.) (http://scitation.aip.org/tpt) grøn pilJ.A.M. Clack and T.P. Toepker: “Magnetic induction experiment”, The Physics Teacher 28, 236 (1990). (Kvantitative målinger på magnet gennem kobberør.) (http://scitation.aip.org/tpt) grøn pilJ. Priest and B. Wade: “A Lenz Law experiment”, The Physics Teacher 30, 106 (1992). (Kvantitative målinger på magnet gennem kobberør.) (http://scitation.aip.org/tpt) grøn pilM.K. Roy, M.K. Harbola, and H.C. Verma: “Demonstration of Lenz's law: Analysis of a magnet falling through a conducting tube”, Am. J. Phys. 75, 728 (2007).

experiments/magnet_in_cobber_tube.txt · Last modified: 2016/04/28 00:54 by svrijn
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